**Introduction to Scientific Discipline Agrophysics — History and Research Objects**

B. Dobrzański, S. Grundas and A. Stępniewski

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/56982

## **1. Introduction**

### **1.1. Agrophysics's definition and scope**

From the very beginning of its existence the definition of Agrophysics as a science was described a number of times. In general, Agrophysics is a branch of natural and agricultural sciences which applies physics into agriculture. Therefore sometimes it is also called agricul‐ tural physics. It explores agricultural materials and processes to describe their physical properties in order to assure best quality of agricultural products or raw material for industry, taking into account the role of environment and other factors. As a field of science, Agrophysics is of interdisciplinary scope and it is closely related to Biophysics. It is however limited strictly to the agricultural environment, i.e., soil, plants and animals and also takes into account the knowledge of Agronomy and Agriculture Engineering.

Agrophysics deals with physical processes in the soil-plant-atmosphere system, taking into account various external factors (climate, impact of the machinery, pollution) and issues related to the growth, harvest, transport, storage and processing of agricultural materials.

Some examples of the wide scope of agrophysical investigation are: developing systems for monitoring and controlling the condition of soil (moisture, salinity etc.) and plant growth (maturity), evaluation of the soil's susceptibility to water and wind erosion, moni‐ toring and diagnosis of soil biological activity, determination of pollution in agricultural products (fruits, vegetables etc.), the assessment of the technological value of grain, evalu‐ ation of quality of fruits and vegetables during their storage and changes of their nutri‐ tion value during storage.

© 2013 Dobrzański et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Dobrzański et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

physics to agriculture. Most attention was given to soil physics, e.g., he studied water-holding capacities, moisture requirements of plants, aeration, movement of water in soils, movement of groundwater, and the drafts of plows. During his last years in Madison he also began studies

Introduction to Scientific Discipline Agrophysics — History and Research Objects

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5

**•** The soil: Its nature, relations and fundamental principles of management. Macmillan, 1895.

F.H. King's observations and investigations could be nowadays regarded as a contribution to the so called sustainable agriculture. He died in 1911 in Madison, Wisconsin and his last two

Beginnings of application of physics in agriculture in Europe were in Soviet Russia. Agro‐ physical research was commenced in Russia in the middle of XX century. Russian physicist Abram Fieodorovich Ioffe (1880–1960) is regarded as the initiator of this branch of science. He studied measuring methods and used them in agriculture, biology and agrochemistry. He studied electromagnetism, radiology, crystals, high-impact physics, thermoelectricity and photoelectricity. He established research laboratories for radioactivity, superconductivity, and nuclear physics. In 1932 Ioffe organized the Institute of Physics and Agriculture in Leningrad (Sankt Petersburg at present) and became its first director. A.F. Ioffe published two funda‐ mental works entitled: Physics and Agriculture (1955), and Physics for Agriculture (1959). His successors included: A.F. Chudnovsky (1910–1985), F.E. Koliasev (1898–1958);P.V. Vershinin (1909–1978); I.B. Revut (1909–1978), S.V. Nerpin (1915–1993), E.I. Ermakov (1929–2006), N.F. Bondarenko's (1928– 2003); I.S. Lisker; A.M. Globus, V.P. Yakushev and others. The research topics undertaken by the above mentioned scientists were: mathematical modeling of agri‐ cultural production, simulation of agrophysical systems and processes; interaction of biolog‐ ical objects with different physical fields (light, gravity, magnetic, electromagnetic, acoustic, electrostatic), information technologies of production management in arable farming and plant growing, agrophysical instrumentation, elaboration of vegetative systems in controlled climate, a new type of coordinate precision agriculture as the first step to the creation of the

The second scientific Institute whose main field of research is Agrophysics was established in Lublin, Poland. Created in 1968 by prof. Bohdan Dobrzański, the Institute of Agrophysics of the Polish Academy of Sciences was soon recognized as a leading research centre not only in

of soil fertility. He has been called the "father" of soil physics in the USA.

King published some books, the titles of which prove his scientific interest:

**•** Irrigation and drainage. Macmillan, 1898. New York.

**•** Physics of agriculture. F.H. King, 1901. Madison, WI.

**•** Soil management. Orange-Judd, 1914. New York.

books were completed and published after his death.

**•** Farmers of forty centuries. F.H. King, 1911. Madison, WI.

New York.

"electronic farmer".

**•** Elementary lessons in physics of agriculture. F.H. King, 1894. Madison, WI.

**•** Ventilation for dwellings, rural schools and stables. F.H. King, 1908. Madison, WI

**Figure 1.** Graphical description of the definition of Agrophysics

The following definition of Agrophysics was recently included in the "Encyclopedia of Agrophysics":

"Agrophysics is a science that studies physical processes and properties affecting plant production. The fundaments (nutrients) and energy (light, heat) transport in the soil– plant–atmosphere and soil–plant–machine–agricultural products–foods continuums and way of their regulation to reach biomass of high quantity and quality with the sustainability to the environment. The knowledge of physical phenomena in agricultural environment allows increasing efficiency of use of water and chemicals in agriculture and decreasing biomass losses during harvest, transport, storage, and processing."

Agrophysics therefore aims at ecological use of agricultural ecosystem to assure best quality of agriculture products and the preservation of agricultural landscapes.

### **2. History**

In the end of XIX century scientists recognized the need of application of physics to agriculture. The pioneer in this field of research was probably Franklin Hiram King. He was born in 1848 in Whitewater Wisconsin USA. He graduated from Cornell University and served as professor of natural sciences at River Falls State Normal School and after that as professor of agricultural physics at the University of Wisconsin. In 1888 the University of Wisconsin called him to the Chair of Agricultural Physics, the first of its kind in America. F.H. King was interested in a wide range of scientific problems but he made his major contributions to the applications of physics to agriculture. Most attention was given to soil physics, e.g., he studied water-holding capacities, moisture requirements of plants, aeration, movement of water in soils, movement of groundwater, and the drafts of plows. During his last years in Madison he also began studies of soil fertility. He has been called the "father" of soil physics in the USA.

King published some books, the titles of which prove his scientific interest:

**Figure 1.** Graphical description of the definition of Agrophysics

Agrophysics":

4 Advances in Agrophysical Research

and processing."

**2. History**

The following definition of Agrophysics was recently included in the "Encyclopedia of

"Agrophysics is a science that studies physical processes and properties affecting plant production. The fundaments

(nutrients) and energy (light, heat) transport in the soil– plant–atmosphere and soil–plant–machine–agricultural

products–foods continuums and way of their regulation to reach biomass of high quantity and quality with the

sustainability to the environment. The knowledge of physical phenomena in agricultural environment allows increasing

efficiency of use of water and chemicals in agriculture and decreasing biomass losses during harvest, transport, storage,

Agrophysics therefore aims at ecological use of agricultural ecosystem to assure best quality

In the end of XIX century scientists recognized the need of application of physics to agriculture. The pioneer in this field of research was probably Franklin Hiram King. He was born in 1848 in Whitewater Wisconsin USA. He graduated from Cornell University and served as professor of natural sciences at River Falls State Normal School and after that as professor of agricultural physics at the University of Wisconsin. In 1888 the University of Wisconsin called him to the Chair of Agricultural Physics, the first of its kind in America. F.H. King was interested in a wide range of scientific problems but he made his major contributions to the applications of

of agriculture products and the preservation of agricultural landscapes.

F.H. King's observations and investigations could be nowadays regarded as a contribution to the so called sustainable agriculture. He died in 1911 in Madison, Wisconsin and his last two books were completed and published after his death.

Beginnings of application of physics in agriculture in Europe were in Soviet Russia. Agro‐ physical research was commenced in Russia in the middle of XX century. Russian physicist Abram Fieodorovich Ioffe (1880–1960) is regarded as the initiator of this branch of science. He studied measuring methods and used them in agriculture, biology and agrochemistry. He studied electromagnetism, radiology, crystals, high-impact physics, thermoelectricity and photoelectricity. He established research laboratories for radioactivity, superconductivity, and nuclear physics. In 1932 Ioffe organized the Institute of Physics and Agriculture in Leningrad (Sankt Petersburg at present) and became its first director. A.F. Ioffe published two funda‐ mental works entitled: Physics and Agriculture (1955), and Physics for Agriculture (1959). His successors included: A.F. Chudnovsky (1910–1985), F.E. Koliasev (1898–1958);P.V. Vershinin (1909–1978); I.B. Revut (1909–1978), S.V. Nerpin (1915–1993), E.I. Ermakov (1929–2006), N.F. Bondarenko's (1928– 2003); I.S. Lisker; A.M. Globus, V.P. Yakushev and others. The research topics undertaken by the above mentioned scientists were: mathematical modeling of agri‐ cultural production, simulation of agrophysical systems and processes; interaction of biolog‐ ical objects with different physical fields (light, gravity, magnetic, electromagnetic, acoustic, electrostatic), information technologies of production management in arable farming and plant growing, agrophysical instrumentation, elaboration of vegetative systems in controlled climate, a new type of coordinate precision agriculture as the first step to the creation of the "electronic farmer".

The second scientific Institute whose main field of research is Agrophysics was established in Lublin, Poland. Created in 1968 by prof. Bohdan Dobrzański, the Institute of Agrophysics of the Polish Academy of Sciences was soon recognized as a leading research centre not only in Eastern and Central Europe, but also in the global research. Numerous professors and younger researchers from the Institute frequently visited leading universities from Western Europe, Japan and the USA, bringing home the knowledge of recent trends and novel methods in the research field. In turn, the high quality of IA staff attracted a number of doctoral students and young researchers from Poland and abroad.This attractiveness, especially to young research‐ ers made the Institute become also a leading educational centre at an advanced level in numerous research areas connected with environment, agriculture and food sector. The results of the research activities undertaken in the Institute were introduced into industry and gave basis for new products and technologies. The outstanding scientists of that period were: I. Dechnik (1929 - 2003), R. Walczak (1943 - 2003), M. Malicki (1939 - 2009), J. Stawiński (1942 - 2005), B. Szot (1933 – 2012), J. Gliński, W. Stępniewski, J. Lipiec, K. Konstankiewicz,

At present, there are more than 100 employees of interdisciplinary character. The scientific staff of the institute constitutes an interdisciplinary team of physicists, chemists, agronomists,

Introduction to Scientific Discipline Agrophysics — History and Research Objects

http://dx.doi.org/10.5772/56982

7

Agrophysics initially focused mainly on the study of soil and plant materials. Over time, this research area started to gradually expand, on the one hand including ever more elements of the soil-plant-atmosphere system, on the other hand, more and more focused on the process of food production and its quality - from the stage of agricultural production through the

Agrophysics began also to be useful in the wider environment, being a part in the study of not only the degradation of soils, but also researching marshy land formation and greenhouse gas emissions. Currently Agrophysics concentrates on a number of agricultural specialties, it is used to interpret interactions, design, control and optimization of processes. It is also widely used in environmental protection, pedology, tillage and plant engineering, agriculture, agri-

Agrophysics was developed also in other countries, initially in Eastern European countries. In Czechoslovakia (Prague) R. Řezniček together with his coworkers (J. Blahovec, J. Pecen, P. Hnilica) conducted some important investigations at the Chair of Physics of Prague Agricul‐ tural University. They concentrated on physical properties of cereal grains and developed some interesting testing methods. In Czech M. Kutilek from Czech Technical University in Prague conducted advanced studies within soil science too. Also in Hungary (Gödöllö and Budapest) researchers carried out studies on physical properties of agricultural materials: soil, seed, grains, vegetables and fruits. In this context the following names should be mentioned: G. Sitkei, I. Husar, G. Várallyay, I. Farkas and others. Also German researchers joined inter‐ national agrophysical society. The universities in Hohenheim (H-D. Kutzbach, E. Schlihting, K. Stahr), Bonn (K.-H Kromer), Kiel (R. Horn), Berlin (G. Wessolek) and in Potsdam (J. Helebrand) were engaged in application of physics in agriculture. The events called "Agrofizik Tagung" were organized on a regular base in Germany. These symposiums gathered scientists interested in this topic from Germany. Agrophysics was researched also in Spain. Spanish scientists were interested both in soil (J. Moreno, M. Aranda and D. de la Rosa) and fruit properties (M. Ruiz-Altisant, J. Caniavate). Belgium has also undertaken serious research activities to become a strong agrophysical centre. Catholic University in Louvain (J. DeBaer‐ demaker, B. Nicolai) and University of Ghent (M. De Boodt, D. Gabriëls) were main centers of agrophysical research there. In France agrophysics was developed in INRA Montfavet (S. Auber, P. Varoquaux), while in Italy the University of Torino (A. Ferero) was the centre of agrophysical studies. Same investigation were also conducted in Belarus and a leader there was I.I. Lishtvan. In Austria prof. W.E.H. Blum interested in some agrophysical aspects of soil

period of storage of agricultural products, their processing until the final product.

horticulturists, biologists, engineers, geographers and mathematicians.

food technology, and others.

**3. Agrophysics in other countries**

sceinces. From Sovakia it is necessarry to mentione Jech.

**Figure 2.** Coworkers of prof. B. Dobrzański from the Instite of Agrophysics at the Conference in Prague 1985 (from left; in the front row: R. Walczak, B. Szot, G. Skubisz, B. Dobrzański, J. Gliński; in the secondrow: M.Molenda, A. Pukos, W. Stępniewski, W. Woźniak, A. Kuczyński, K. Konstankiewicz, J. Lipiec)

The main fields of scientific activity of the Institute of Agrophysics PAS were as follows: investigation of physical and physical–chemical processes of mass and energy exchange in the soil – plant – atmosphere system, physical properties of agricultural materials and processes affecting plant production as well as processes related to gathering, transport and storage of agricultural materials.

The main feature of these studies was the elaboration of new theoretical and experimental research methods, developing of physical – mathematical models and their experimental verification, processing of data, taking into account their variabilityin time and space. Data bases and thematic maps created in this process can be used in practice for agricultural and environmental protection.

At present, there are more than 100 employees of interdisciplinary character. The scientific staff of the institute constitutes an interdisciplinary team of physicists, chemists, agronomists, horticulturists, biologists, engineers, geographers and mathematicians.

Agrophysics initially focused mainly on the study of soil and plant materials. Over time, this research area started to gradually expand, on the one hand including ever more elements of the soil-plant-atmosphere system, on the other hand, more and more focused on the process of food production and its quality - from the stage of agricultural production through the period of storage of agricultural products, their processing until the final product.

Agrophysics began also to be useful in the wider environment, being a part in the study of not only the degradation of soils, but also researching marshy land formation and greenhouse gas emissions. Currently Agrophysics concentrates on a number of agricultural specialties, it is used to interpret interactions, design, control and optimization of processes. It is also widely used in environmental protection, pedology, tillage and plant engineering, agriculture, agrifood technology, and others.

## **3. Agrophysics in other countries**

Eastern and Central Europe, but also in the global research. Numerous professors and younger researchers from the Institute frequently visited leading universities from Western Europe, Japan and the USA, bringing home the knowledge of recent trends and novel methods in the research field. In turn, the high quality of IA staff attracted a number of doctoral students and young researchers from Poland and abroad.This attractiveness, especially to young research‐ ers made the Institute become also a leading educational centre at an advanced level in numerous research areas connected with environment, agriculture and food sector. The results of the research activities undertaken in the Institute were introduced into industry and gave basis for new products and technologies. The outstanding scientists of that period were: I. Dechnik (1929 - 2003), R. Walczak (1943 - 2003), M. Malicki (1939 - 2009), J. Stawiński (1942 -

2005), B. Szot (1933 – 2012), J. Gliński, W. Stępniewski, J. Lipiec, K. Konstankiewicz,

**Figure 2.** Coworkers of prof. B. Dobrzański from the Instite of Agrophysics at the Conference in Prague 1985 (from left; in the front row: R. Walczak, B. Szot, G. Skubisz, B. Dobrzański, J. Gliński; in the secondrow: M.Molenda, A. Pukos,

The main fields of scientific activity of the Institute of Agrophysics PAS were as follows: investigation of physical and physical–chemical processes of mass and energy exchange in the soil – plant – atmosphere system, physical properties of agricultural materials and processes affecting plant production as well as processes related to gathering, transport and storage of

The main feature of these studies was the elaboration of new theoretical and experimental research methods, developing of physical – mathematical models and their experimental verification, processing of data, taking into account their variabilityin time and space. Data bases and thematic maps created in this process can be used in practice for agricultural and

W. Stępniewski, W. Woźniak, A. Kuczyński, K. Konstankiewicz, J. Lipiec)

agricultural materials.

6 Advances in Agrophysical Research

environmental protection.

Agrophysics was developed also in other countries, initially in Eastern European countries. In Czechoslovakia (Prague) R. Řezniček together with his coworkers (J. Blahovec, J. Pecen, P. Hnilica) conducted some important investigations at the Chair of Physics of Prague Agricul‐ tural University. They concentrated on physical properties of cereal grains and developed some interesting testing methods. In Czech M. Kutilek from Czech Technical University in Prague conducted advanced studies within soil science too. Also in Hungary (Gödöllö and Budapest) researchers carried out studies on physical properties of agricultural materials: soil, seed, grains, vegetables and fruits. In this context the following names should be mentioned: G. Sitkei, I. Husar, G. Várallyay, I. Farkas and others. Also German researchers joined inter‐ national agrophysical society. The universities in Hohenheim (H-D. Kutzbach, E. Schlihting, K. Stahr), Bonn (K.-H Kromer), Kiel (R. Horn), Berlin (G. Wessolek) and in Potsdam (J. Helebrand) were engaged in application of physics in agriculture. The events called "Agrofizik Tagung" were organized on a regular base in Germany. These symposiums gathered scientists interested in this topic from Germany. Agrophysics was researched also in Spain. Spanish scientists were interested both in soil (J. Moreno, M. Aranda and D. de la Rosa) and fruit properties (M. Ruiz-Altisant, J. Caniavate). Belgium has also undertaken serious research activities to become a strong agrophysical centre. Catholic University in Louvain (J. DeBaer‐ demaker, B. Nicolai) and University of Ghent (M. De Boodt, D. Gabriëls) were main centers of agrophysical research there. In France agrophysics was developed in INRA Montfavet (S. Auber, P. Varoquaux), while in Italy the University of Torino (A. Ferero) was the centre of agrophysical studies. Same investigation were also conducted in Belarus and a leader there was I.I. Lishtvan. In Austria prof. W.E.H. Blum interested in some agrophysical aspects of soil sceinces. From Sovakia it is necessarry to mentione Jech.

Agrophysics was developed not only in Europe. A fundamental publication on this topic "Physical Properties of Agricultural Products" has been written by N.N. Mohsenin – scientist of Iranian origin who worked in the USA. Prof. A. Tabatabaeefar is a continuator of Mohsenin agrophysical research in Iran. There were also other scientists interested in agricultural physics i.e. S. Gunasekaran, O.R. Kunze, J.I. Ross, G. Brusevitz, F. McClure, Y.A. Pachepsky, S.A. Thompson, P.P. Chen and others. Some topics of applied physics in agriculture were under‐ taken in Japan (R. Hatano) and China (T. Ren,).

A number of scientific papers that were submitted and presented during the above mentioned conferences were published both in conference materials as well as in special issues of scientific

Introduction to Scientific Discipline Agrophysics — History and Research Objects

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9

Institute of Agrophysic of the Polish Academy of Sciences is also the publisher of an outstand‐ ing scientific journal entitled "**International Agrophysics**". The editorial board states that: "the journal focuses on physical properties and processes affecting biomass production and processing. The main topics are: mass (water, air, plant nutrients) and energy (light, heat) transport in the soil-plant-atmosphere continuum, ways of their regulation in order to reach biomass of high quantity and quality. The description of new methods and devices for measurements of the physical properties of agro- and biomaterials are published. The journal is also open to wider aspects of environmental and agricultural physics". The present Editor-

International Agrophysics is indexed by Journal Citation Reports with 1,574 impact factor.

A second journal published by the Institute of Agrophysics is "Acta Agrophysica". Acta Agrophysica has been published since 1993. At the beginning it contained mainly monogra‐ phies and dissertations which were published irregularly. From 2012 Acta Agrophysica is a quarterly. It publishes papers presenting the results of fundamental and applied studies from the field of application of physics for the solution of problems relating to the management and protection of the natural environment, sustainable agriculture, and food processing. Papers can be published both in Polish and English. The present Editor-in-Chief is prof. J. Horabik.

The third journal published by the Institute of Agrophysics is "Acta Agrophysica Monogra‐ phiae" which publishes reviewed papers based on original research results as well as mono‐ graphs pertaining to the field of agrophysics. The monographs are published in Polish or

In order to facilitate international collaboration and allow unification of terminology, a number of bilingual and multilingual dictionary of agrophysical terms (nomenclature) was prepared under editorial supervision of prof. Ryszard Dębicki and prof. Jan Gliński. The following

"Atlas of the Redox Properties of Arable Soils in Poland" prepared by Ostrowski, J.; Stęp‐ niewska, Z.; Stępniewski, W.; Gliński, J. was published 1996. It contains a wide range of data on soils in Poland presented in the form of cartographic maps. The Atlas gives a comprehensive

languages were taken into consideration: English, Russian, French, Spanish, German.

The above mentioned journals are available in electronic versions on the internet.

English. The present Editor-in-Chief is prof. J. Horabik.

**6. Dictionaries and books, maps**

journals.

**5. Agrophysical journals**

in-Chief is prof. J. Gliński.

In Canada at the Guelph University physics in agriculture was practiced by number of researchers (W.K. Bilanski, R.L. Kushwaha). Also at University of Saskatchewan F. Sosulski. Agrophysics was developed even in New Zealand by C.J. Studman.

In Israel some aspects of agrophysics were studied by I. Shmulevich, E. Bresler, K. Peleg.

The above mentioned names and centres do not exhaust the list of places and persons who conduct their investigations in the field of applied physics in agriculture. These are only examples of people who cooperated with scientists from the Institute of Agrophysics PAS proving that agrophysics is a world-wide recognized science discipline.

## **4. Agrophysical conferences**

Conferences on Agrophysics have always been an occasion for long discussionson all aspects of physical, physicochemical and biological processes of mass and energy exchange in soilplant-atmosphere system and of plant production, as well as characteristics of agricultural products and materials, agrophysical measuring methods, soil degradation and remediation problems.

Since Agrophysics became a widely practiced discipline of science there were already a number of agrophysical conferences organized. They gathered scientists which main research interests focus on physics in agriculture. The conferences were organized as follows:

A number of scientific papers that were submitted and presented during the above mentioned conferences were published both in conference materials as well as in special issues of scientific journals.

## **5. Agrophysical journals**

Agrophysics was developed not only in Europe. A fundamental publication on this topic "Physical Properties of Agricultural Products" has been written by N.N. Mohsenin – scientist of Iranian origin who worked in the USA. Prof. A. Tabatabaeefar is a continuator of Mohsenin agrophysical research in Iran. There were also other scientists interested in agricultural physics i.e. S. Gunasekaran, O.R. Kunze, J.I. Ross, G. Brusevitz, F. McClure, Y.A. Pachepsky, S.A. Thompson, P.P. Chen and others. Some topics of applied physics in agriculture were under‐

In Canada at the Guelph University physics in agriculture was practiced by number of researchers (W.K. Bilanski, R.L. Kushwaha). Also at University of Saskatchewan F. Sosulski.

In Israel some aspects of agrophysics were studied by I. Shmulevich, E. Bresler, K. Peleg.

The above mentioned names and centres do not exhaust the list of places and persons who conduct their investigations in the field of applied physics in agriculture. These are only examples of people who cooperated with scientists from the Institute of Agrophysics PAS

Conferences on Agrophysics have always been an occasion for long discussionson all aspects of physical, physicochemical and biological processes of mass and energy exchange in soilplant-atmosphere system and of plant production, as well as characteristics of agricultural products and materials, agrophysical measuring methods, soil degradation and remediation

Since Agrophysics became a widely practiced discipline of science there were already a number of agrophysical conferences organized. They gathered scientists which main research

interests focus on physics in agriculture. The conferences were organized as follows:

taken in Japan (R. Hatano) and China (T. Ren,).

8 Advances in Agrophysical Research

**4.

Agrophysics was developed even in New Zealand by C.J. Studman.

proving that agrophysics is a world-wide recognized science discipline.

Institute of Agrophysic of the Polish Academy of Sciences is also the publisher of an outstand‐ ing scientific journal entitled "**International Agrophysics**". The editorial board states that: "the journal focuses on physical properties and processes affecting biomass production and processing. The main topics are: mass (water, air, plant nutrients) and energy (light, heat) transport in the soil-plant-atmosphere continuum, ways of their regulation in order to reach biomass of high quantity and quality. The description of new methods and devices for measurements of the physical properties of agro- and biomaterials are published. The journal is also open to wider aspects of environmental and agricultural physics". The present Editorin-Chief is prof. J. Gliński.

International Agrophysics is indexed by Journal Citation Reports with 1,574 impact factor.

A second journal published by the Institute of Agrophysics is "Acta Agrophysica". Acta Agrophysica has been published since 1993. At the beginning it contained mainly monogra‐ phies and dissertations which were published irregularly. From 2012 Acta Agrophysica is a quarterly. It publishes papers presenting the results of fundamental and applied studies from the field of application of physics for the solution of problems relating to the management and protection of the natural environment, sustainable agriculture, and food processing. Papers can be published both in Polish and English. The present Editor-in-Chief is prof. J. Horabik.

The third journal published by the Institute of Agrophysics is "Acta Agrophysica Monogra‐ phiae" which publishes reviewed papers based on original research results as well as mono‐ graphs pertaining to the field of agrophysics. The monographs are published in Polish or English. The present Editor-in-Chief is prof. J. Horabik.

The above mentioned journals are available in electronic versions on the internet.

## **6. Dictionaries and books, maps**

In order to facilitate international collaboration and allow unification of terminology, a number of bilingual and multilingual dictionary of agrophysical terms (nomenclature) was prepared under editorial supervision of prof. Ryszard Dębicki and prof. Jan Gliński. The following languages were taken into consideration: English, Russian, French, Spanish, German.

"Atlas of the Redox Properties of Arable Soils in Poland" prepared by Ostrowski, J.; Stęp‐ niewska, Z.; Stępniewski, W.; Gliński, J. was published 1996. It contains a wide range of data on soils in Poland presented in the form of cartographic maps. The Atlas gives a comprehensive information on soils in Poland and can be regarded as a research tool for studying spatial characteristics of agriculture. Practical application of the database lays in the power to generate, for the first time in the world, the thematic maps on spatial differentiation of the redox soil properties throughout the country. A set of these maps has been presented in the published atlas.

**•** to develop a scientific network with universities,

with a contribution to research projects,

obtain more funds for research.

**9. Polish Society of Agrophysics**

**Figure 3.** Location of PSA branches in Poland

European funds.

**•** to make the IA more attractive for students by combining post-graduate and doctoral studies

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**•** to establish a Foundation for Development of Agrophysical Research in order to be able to

The prolongation of the existence of the CoE and the consequence of this prolongation was a possibility for dynamic development of the structural base of the Institute. The full renovation of buildings as well as thorough exchange of research equipment was accomplished thanks to

Polish Society of Agrophysics (PSA) was founded in 1996 in Lublin. The initiator and the first president of PSA was prof. Bogusław Szot (1933 - 2012). He has been managing the Society until his death in October 2012. During his presidency ten branches in major scientific centers in Poland were established, where agrophysical investigations are performed (Fig. 3.). The Society is very active and every year it organizes meetings, seminars and symposia. Today PSA comprises over 360 members, among whom over 150 hold the title of full professor.

The main goal of the Society is to agglomerate researchers who conduct their research in the field of agrophysics. The Society has organized nine national and international conferences with over 1400 participants (115 of them from 29 countries outside Poland). Every conference has its own book of abstract, where the most recent results are presented. The most important papers are published in International Agrophysics and Acta Agrophysica – both journals

The last but most fundamental publication on Agrophysics is the "Encyclopedia of Agrophy‐ sics" edited by J. Gliński, J. Horabik and J. Lipiec by Springer in 2011. This book provides an up-to-date information on the physical properties and processes affecting the quality of the environment and plant production. Encyclopedia of Agrophysics is a publication comple‐ mentary to the Encyclopedia of Soil Science, (November 2007) which has been published in the field of Earth sciences series of Springer. The Encyclopedia presents a set of about 250 informative articles and ca 400 glossary terms covering all aspects of Agrophysics. It contains 450 illustrations on more than 1000 pages.

## **7. Data banks (soil probe bank)**

One of the comprehensive accomplishment of the Institute of Agrophysics PAS is the bank of soil samples collected all over Poland. The collection consists of over a thousand profiles (3 levels) and their full characteristics. This is a unique set of samples which can enable scientists to monitor changes of agriculture environment in Poland.

## **8. Agrophysics — European centre of excellence**

The Centre Of Excellence For Applied Physics In Sustainable Agriculture "AGROPHYSICS" was created on February 28-th. 2003, within the scheme of the 5-th. Framework Programme of the European Union. The project was realized for three years and ended on February 28th2006. The main goal of the project was to support the research potential of the region and strengthen its integration with the European Research Area.

The main points of the action plan of the CoE were:

**•** to develop a scientific network with universities,

information on soils in Poland and can be regarded as a research tool for studying spatial characteristics of agriculture. Practical application of the database lays in the power to generate, for the first time in the world, the thematic maps on spatial differentiation of the redox soil properties throughout the country. A set of these maps has been presented in the

The last but most fundamental publication on Agrophysics is the "Encyclopedia of Agrophy‐ sics" edited by J. Gliński, J. Horabik and J. Lipiec by Springer in 2011. This book provides an up-to-date information on the physical properties and processes affecting the quality of the environment and plant production. Encyclopedia of Agrophysics is a publication comple‐ mentary to the Encyclopedia of Soil Science, (November 2007) which has been published in the field of Earth sciences series of Springer. The Encyclopedia presents a set of about 250 informative articles and ca 400 glossary terms covering all aspects of Agrophysics. It contains

One of the comprehensive accomplishment of the Institute of Agrophysics PAS is the bank of soil samples collected all over Poland. The collection consists of over a thousand profiles (3 levels) and their full characteristics. This is a unique set of samples which can enable scientists

The Centre Of Excellence For Applied Physics In Sustainable Agriculture "AGROPHYSICS" was created on February 28-th. 2003, within the scheme of the 5-th. Framework Programme of the European Union. The project was realized for three years and ended on February 28th2006. The main goal of the project was to support the research potential of the region and strengthen

**•** to develop programmes aimed at significant technological applications, while preserving

**•** to intensify activities in attracting funds from the State Committee for Scientific Research (KBN; now – the Ministry of Science and Higher Education) under research grants,

**•** to concentrate on modern research fields with potential applications in industry,

**•** to expand the Institute's activities towards market-oriented research,

**•** to participate in European projects within European research programmes,

published atlas.

10 Advances in Agrophysical Research

450 illustrations on more than 1000 pages.

**7. Data banks (soil probe bank)**

to monitor changes of agriculture environment in Poland.

**8. Agrophysics — European centre of excellence**

its integration with the European Research Area.

high standard of fundamental research,

The main points of the action plan of the CoE were:

**•** to start co-operation with Polish industry and SMEs,

The prolongation of the existence of the CoE and the consequence of this prolongation was a possibility for dynamic development of the structural base of the Institute. The full renovation of buildings as well as thorough exchange of research equipment was accomplished thanks to European funds.

## **9. Polish Society of Agrophysics**

Polish Society of Agrophysics (PSA) was founded in 1996 in Lublin. The initiator and the first president of PSA was prof. Bogusław Szot (1933 - 2012). He has been managing the Society until his death in October 2012. During his presidency ten branches in major scientific centers in Poland were established, where agrophysical investigations are performed (Fig. 3.). The Society is very active and every year it organizes meetings, seminars and symposia. Today PSA comprises over 360 members, among whom over 150 hold the title of full professor.

**Figure 3.** Location of PSA branches in Poland

The main goal of the Society is to agglomerate researchers who conduct their research in the field of agrophysics. The Society has organized nine national and international conferences with over 1400 participants (115 of them from 29 countries outside Poland). Every conference has its own book of abstract, where the most recent results are presented. The most important papers are published in International Agrophysics and Acta Agrophysica – both journals edited at the Institute of Agrophysics PAS. Current information on the activities of PSA is distributed through its Information Bulletin.

achieved by publishing (Scientific Publishing House of FRNA) in the field of natural sciences and application of physics in agriculture. According to the up-to-date techniques, the Foun‐ dation proposed e-files i.e. electronic publications on CD and DVD instead traditionally printed books. The Foundation also sponsors various initiatives and initiates actions toward

Introduction to Scientific Discipline Agrophysics — History and Research Objects

http://dx.doi.org/10.5772/56982

13

For many years a workshop for prototype apparatus production was being organized at the Institute of Agophysics PAS in Lublin. A number of pioneer measuring techniques were elaborated and used in innovative apparatus. Both construction and production of this equipment was realized at the Institute. The founder and the first manager of the workshop

Under this activity a measuring systems for determination of moisture content and salinity of soil and other porous materials has been elaborated. The measuring techniques are based on the Time-Domain Reflectometry (TDR) which is worldwide patented. In the last years an innovative silo for drying and safe storage of rapeseed was constructed. The silo allows automated post-harvest drying, cooling, and storage of rapeseeds in neutral gas atmosphere to assure best quality of raw material for oil production. It prevents the development of heat processes as well as moulds and fungi growth in stored seeds. Also some prototype measuring apparatus were elaborated in order to evaluate quality parameters of fruit tissue especially

All the above mentioned activities, institutions and persons prove the necessity and usability of Agrophysics as a branch of applied science, which can help to solve current problems in

[1] Dobrzanski, B. (1986). Możliwości rozwoju agrofizyki. Wykład z okazji nadania tytu‐

łu Doktora Honoris Causa ART w Olsztynie, Kaseta video, ART, Olsztyn.

agriculture and which can benefit in progress of this part of economy.

Institute of Agrophysics Polish Academy of Sciences, Lublin, Poland

B. Dobrzański, S. Grundas and A. Stępniewski

popularization of agrophysics as science.

was M. Grochowicz, PhD.

apple tissue.

**Author details**

**References**

**12. Prototype apparatus and investigation methods**

## **10. Scientific Committee of Agrophysics of Polish Academy of Sciences**

The Committee of Agrophysics of Polish Academy of Sciences was established in 1981.

The Scientific Committees of the Polish Academy of Sciences are self-governing, nationwide representation of various disciplines or groups as well as interdisciplinary scientific problems integrating scholars throughout Poland. The scientific committee includes the Members of the Polish Academy of Sciences of the relevant specialty (outstanding scientists), eminent re‐ searchers representing universities, institutes of the Polish Academy of Sciences and the scientific institutes and research departments, as well as representatives of other institutions, including economic and social organizations. The scientific committees of the Polish Academy of Sciences are the most representative group of experts in the discipline.

The main task of the Scientific Committee of Agrophysics is to promote research of physical and physicochemical properties of the natural environment with particular emphasis on the system: soil-plant-atmosphere-machine-crops, agricultural-machine-food products. At present the chairman of the Committee is prof. Bohdan Dobrzański Jr.

Actually there are three sections operating within the structure of the Committee:

Since the beginning of its existence the Committee's special attention was directed to the integration of the scientific community and its involvement in the process of creatively solving important problems in agricultural research. The Committee in its activities focused also on identifying the main areas of research and science policy in the agrophysics. In previous years the Committee also financed research projects in the field of agrophysics. It has developed extensive cooperation with other committees working in the field of agricultural sciences. It also promoted international cooperation as a partner institution in organization of interna‐ tional conferences.

## **11. Foundation for Development of Agrophysical Sciences (FRNA)**

Foundation for Development of Agrophysical Sciences was established for the purpose of supporting and promoting the development of agrophysical research and activity of the Institute of Agrophysics PAS. The implementation of the main goals of the Foundation is achieved by publishing (Scientific Publishing House of FRNA) in the field of natural sciences and application of physics in agriculture. According to the up-to-date techniques, the Foun‐ dation proposed e-files i.e. electronic publications on CD and DVD instead traditionally printed books. The Foundation also sponsors various initiatives and initiates actions toward popularization of agrophysics as science.

## **12. Prototype apparatus and investigation methods**

For many years a workshop for prototype apparatus production was being organized at the Institute of Agophysics PAS in Lublin. A number of pioneer measuring techniques were elaborated and used in innovative apparatus. Both construction and production of this equipment was realized at the Institute. The founder and the first manager of the workshop was M. Grochowicz, PhD.

Under this activity a measuring systems for determination of moisture content and salinity of soil and other porous materials has been elaborated. The measuring techniques are based on the Time-Domain Reflectometry (TDR) which is worldwide patented. In the last years an innovative silo for drying and safe storage of rapeseed was constructed. The silo allows automated post-harvest drying, cooling, and storage of rapeseeds in neutral gas atmosphere to assure best quality of raw material for oil production. It prevents the development of heat processes as well as moulds and fungi growth in stored seeds. Also some prototype measuring apparatus were elaborated in order to evaluate quality parameters of fruit tissue especially apple tissue.

All the above mentioned activities, institutions and persons prove the necessity and usability of Agrophysics as a branch of applied science, which can help to solve current problems in agriculture and which can benefit in progress of this part of economy.

## **Author details**

edited at the Institute of Agrophysics PAS. Current information on the activities of PSA is

**10. Scientific Committee of Agrophysics of Polish Academy of Sciences**

The Scientific Committees of the Polish Academy of Sciences are self-governing, nationwide representation of various disciplines or groups as well as interdisciplinary scientific problems integrating scholars throughout Poland. The scientific committee includes the Members of the Polish Academy of Sciences of the relevant specialty (outstanding scientists), eminent re‐ searchers representing universities, institutes of the Polish Academy of Sciences and the scientific institutes and research departments, as well as representatives of other institutions, including economic and social organizations. The scientific committees of the Polish Academy

The main task of the Scientific Committee of Agrophysics is to promote research of physical and physicochemical properties of the natural environment with particular emphasis on the system: soil-plant-atmosphere-machine-crops, agricultural-machine-food products. At

**•** Section of Physics Application in Engineering of Agricultural Production and in Food

**•** Section for Physical Measurement Techniques for the Agricultural Environment Protection,

Since the beginning of its existence the Committee's special attention was directed to the integration of the scientific community and its involvement in the process of creatively solving important problems in agricultural research. The Committee in its activities focused also on identifying the main areas of research and science policy in the agrophysics. In previous years the Committee also financed research projects in the field of agrophysics. It has developed extensive cooperation with other committees working in the field of agricultural sciences. It also promoted international cooperation as a partner institution in organization of interna‐

**•** Section of Physical Methods of Evaluation of the Quality of Agricultural Products.

**11. Foundation for Development of Agrophysical Sciences (FRNA)**

Foundation for Development of Agrophysical Sciences was established for the purpose of supporting and promoting the development of agrophysical research and activity of the Institute of Agrophysics PAS. The implementation of the main goals of the Foundation is

The Committee of Agrophysics of Polish Academy of Sciences was established in 1981.

of Sciences are the most representative group of experts in the discipline.

present the chairman of the Committee is prof. Bohdan Dobrzański Jr.

Actually there are three sections operating within the structure of the Committee:

distributed through its Information Bulletin.

12 Advances in Agrophysical Research

Technology,

tional conferences.

B. Dobrzański, S. Grundas and A. Stępniewski

Institute of Agrophysics Polish Academy of Sciences, Lublin, Poland

## **References**

[1] Dobrzanski, B. (1986). Możliwości rozwoju agrofizyki. Wykład z okazji nadania tytu‐ łu Doktora Honoris Causa ART w Olsztynie, Kaseta video, ART, Olsztyn.

[2] Dobrzanski, B. (1981). Badania w zakresie fizyki i fizykochemii gleb. Kosmos, , 2, 135-139.

**Section 2**

**Physical Properties of Soil and Environment**

**Physical Properties of Soil and Environment**

[2] Dobrzanski, B. (1981). Badania w zakresie fizyki i fizykochemii gleb. Kosmos, , 2,

[3] Dobrzanski, B, Dechnik, I, & Glinski, J. (1979). Rozwój badań agrofizycznych w

[4] Dobrzanski, B, Glinski, J, & Szot, B. (1988). Agrophysical investigations in Poland at present and in future. Physical properties of agricultural materials and products.

[6] Haman, J, Horabik, J, & Pukos, A. (1985). Mechanical investigations of agricultural materials in the Institute of Agrophysics. Zesz. Probl. Post. Nauk Roln., z. , 304, 9-16.

[7] Szot, B. Dobrzański jr B., (1995). Agrofizyka dla techniki rolniczej. Zesz. Probl. Post.

[8] Tanner, C. B, & Simonson, R. W. (1993). Franklin Hiram King- Pioneer Scientist. Soil

[5] Glinski, J, Horabik, J, & Lipiec, J. (2011). Encyclopedia of Agrophysics. Springer.

135-139.

14 Advances in Agrophysical Research

Polsce. Post. Nauk Roln., 5.

Nauk Roln., z. , 424, 79-86.

[9] http://www.agrophys.ru/

[10] http://www.ipan.lublin.pl/

Hemisphere Publ. Corp., New York, , 873-976.

Science Society of America Journal , 57(1)

[11] http://www.international-agrophysics.org/

[13] http://www.acta-agrophysica-monographiae.org/

[12] http://www.acta-agrophysica.org/

[14] http://www.komagrof.pan.pl/

**Chapter 2**

**Aquametry in Agrophysics**

Andrzej Wilczek

**1. Introduction**

http://dx.doi.org/10.5772/52505

Wojciech Skierucha, Agnieszka Szypłowska and

Aquametry is a part of metrology that uses the available measurement techniques in the measurement of water content in solid, liquid and heterogeneous materials. A similar branch of metrology, called hygrometry, deals with determination of the water vapour con‐ tent in air and other gases (Kraszewski, 2001). The aim of agrophysics is to apply physical methods and techniques for studies of materials and processes which take place in agricul‐ ture. Possible test objects may therefore include soil, fruit, vegetables, intermediate and final

Historically, the primary application of aquametry in agrophysics is the measurement of soil water content. The available soil water content measurement techniques are evolving to fol‐ low the technological development in metrology. Soil is an inhomogeneous and complex medium in physical, chemical and biological aspects, which makes determination of soil wa‐ ter content a difficult technical and methodological problem. New moisture measurement methodologies and techniques, developed for the purpose of soil testing, in many cases have been later adapted to other agrophysical fields of interest, including storage of grain, conservation and quality testing of food products, transportation, climate change research

Water is the basic biological solvent and an absolutely necessary component of every life form on Earth. The shortage of water is the main growth limiting factor for plants and other organisms in arid regions. Sufficient continuous supply of fresh water is obviously a funda‐ mental necessity for human and animal life. Because water is a deficit resource in many parts of the world, the sustainable and harmonious development of societies needs reasona‐ ble and responsible water management policy. Continuous long-term monitoring of soil moisture on local and global scales, extremely significant for agriculture (including irriga‐

> © 2013 Skierucha et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2013 Skierucha et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Additional information is available at the end of the chapter

products of the food industry, grain, oils, etc.

and safety measures against floods and landslides.

## **Chapter 2**

## **Aquametry in Agrophysics**

Wojciech Skierucha, Agnieszka Szypłowska and Andrzej Wilczek

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/52505

## **1. Introduction**

Aquametry is a part of metrology that uses the available measurement techniques in the measurement of water content in solid, liquid and heterogeneous materials. A similar branch of metrology, called hygrometry, deals with determination of the water vapour con‐ tent in air and other gases (Kraszewski, 2001). The aim of agrophysics is to apply physical methods and techniques for studies of materials and processes which take place in agricul‐ ture. Possible test objects may therefore include soil, fruit, vegetables, intermediate and final products of the food industry, grain, oils, etc.

Historically, the primary application of aquametry in agrophysics is the measurement of soil water content. The available soil water content measurement techniques are evolving to fol‐ low the technological development in metrology. Soil is an inhomogeneous and complex medium in physical, chemical and biological aspects, which makes determination of soil wa‐ ter content a difficult technical and methodological problem. New moisture measurement methodologies and techniques, developed for the purpose of soil testing, in many cases have been later adapted to other agrophysical fields of interest, including storage of grain, conservation and quality testing of food products, transportation, climate change research and safety measures against floods and landslides.

Water is the basic biological solvent and an absolutely necessary component of every life form on Earth. The shortage of water is the main growth limiting factor for plants and other organisms in arid regions. Sufficient continuous supply of fresh water is obviously a funda‐ mental necessity for human and animal life. Because water is a deficit resource in many parts of the world, the sustainable and harmonious development of societies needs reasona‐ ble and responsible water management policy. Continuous long-term monitoring of soil moisture on local and global scales, extremely significant for agriculture (including irriga‐

© 2013 Skierucha et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Skierucha et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

tion), environmental protection, meteorology, climatology, scientific research and water management, requires reliable measurement techniques. The development of remote and proximal soil moisture determination methods is therefore one of the most important aims of aquametry.

Another useful quantity is the volumetric water content given by the relation

lated on a wet basis as follows

*<sup>θ</sup><sup>v</sup>* <sup>=</sup> *<sup>V</sup> <sup>w</sup> Vb*

*<sup>θ</sup><sup>v</sup>* <sup>=</sup>*<sup>ξ</sup> <sup>ρ</sup><sup>b</sup> ρw*

each other and another compatible polar chemical groups.

other chemical constituents of a given material.

where *Vw* is the volume of water contained in a given body and *Vb* is the bulk volume of this body. Knowing the bulk density of the tested material, *ρ<sup>b</sup>* =*mb* / *Vb* , and the density of water, *ρw*, the volumetric water content may be expressed by the mass water content calcu‐

The total amount of water contained in a given body does not fully determine all of its mois‐ ture related properties. The structure and chemical composition of a given body can greatly influence the properties of contained water. The molecule of water, consisting of two hydro‐ gen atoms bound to an atom of oxygen, exhibits polar structure. It may be described as a regular tetrahedron, with the oxygen atom in the centre and the hydrogen atoms with parti‐ al positive charges in two corners. Free corners of the tetrahedron are occupied by two elec‐ tron orbitals. Effectively, though a water molecule is not electrically charged, it possesses an electrical dipole moment. Water molecules are thus enabled to form hydrogen bonds with

Because of the unique properties of water molecules, generally it is possible to distinguish three states of water in a moist material (Hillel, 2004; Lewicki, 2004; Chen and Or, 2006):

**1.** Bound water – consisting of water molecules bound by hydrogen bonds to a macromo‐ lecule (so called structure water – its molecules are immobilised and become structural parts of a macromolecule) and of oriented water molecules forming hydration shells around ions, polar chemical groups and whole macromolecules (so called hydration water). Number of water molecules in a hydration shell, as well as their orientation, dis‐ tortion and number of layers depend on the surface charge density of an ion or on a structure of a macromolecule in question. Furthermore, even non-polar compounds in‐ teract with water, affecting the distribution and orientation of surrounding water mole‐

**2.** Capillary water – because water exhibits surface tension, in non-hydrophobic porous materials water can be held in the pores through a capillary pressure, defined as a dif‐ ference of pressures above and below the surface of the water meniscus. It causes the effect of a capillary rise above the free water surface to the height defined by the surface tension, contact angle, capillary radius and the difference between the water and gas (air) densities. Water is more easily held in smaller pores than in large ones. Capillary

water is at equilibrium with the films of bound water adsorbed on the surfaces.

**3.** Free water – movement of its molecules is not constrained by any kinds of bonds with

cules – the effect is called hydrophobic hydration (Lewicki, 2004).

(3)

19

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505

(4)

The practical agricultural applications of water content determination are not restricted to soil measurements. The storage of grain, seeds and other crops, as well as their processing and resultant food products, usually require control of moisture level to prevent spoilage and proliferation of pests, to preserve their quality and extend their shelf life, and to ensure appropriate technological processing conditions. Another fundamental application of aqua‐ metry is therefore the evaluation of the state and content of water in various materials of ag‐ ricultural origin, including food products. Because of high variability of such materials, which may be liquids, solids, porous materials or heterogeneous mixtures of complicated structure and chemical composition, the development of appropriate aquametry techniques may become a challenging endeavour.

Due to the recent technological development in the fields of electronics, informatics, micro‐ wave techniques and mobile communication, there is a significant progress in indirect die‐ lectric measurement methods, especially the broadband spectroscopic techniques. These methods enable fast, selective and non-destructive measurements using portable meters and sensors that can be applied in real time testing during production processes and monitoring of storage of various agricultural materials and food products. On the other hand, there are several significant obstacles hampering the development of effective dielectric techniques for determination of moisture content and related material properties. The main difficulties lie in the necessity of performing basic research to understand water-involving physical and chemical processes at micro- and macroscopic scales, mechanisms of polarization and influ‐ ence of electromagnetic waves on studied materials, development of selective sensor techni‐ ques and achieving the required accuracy.

#### **1.1. Physical fundamentals and definitions**

The amount of water in a given body may be described by the mass or volume of water rela‐ tive to the mass or volume of the whole moist object or just the appropriate dry mass (Kras‐ zewski, 2001; Hillel, 2004). On a wet basis, the mass water content of a body is equal to the mass of the water, *mw*, divided by the bulk mass of the moist body, *mb*, which is the sum of the mass of the water and the mass of the dry material, *md*

$$\xi = \frac{m\_v}{m\_b} \; \; \; m\_b = m\_w + m\_d \tag{1}$$

The mass water content on a dry basis is defined as the ratio of the mass of water to the mass of the dry material

$$
\eta = \frac{m\_w}{m\_d} \tag{2}
$$

Another useful quantity is the volumetric water content given by the relation

tion), environmental protection, meteorology, climatology, scientific research and water management, requires reliable measurement techniques. The development of remote and proximal soil moisture determination methods is therefore one of the most important aims

The practical agricultural applications of water content determination are not restricted to soil measurements. The storage of grain, seeds and other crops, as well as their processing and resultant food products, usually require control of moisture level to prevent spoilage and proliferation of pests, to preserve their quality and extend their shelf life, and to ensure appropriate technological processing conditions. Another fundamental application of aqua‐ metry is therefore the evaluation of the state and content of water in various materials of ag‐ ricultural origin, including food products. Because of high variability of such materials, which may be liquids, solids, porous materials or heterogeneous mixtures of complicated structure and chemical composition, the development of appropriate aquametry techniques

Due to the recent technological development in the fields of electronics, informatics, micro‐ wave techniques and mobile communication, there is a significant progress in indirect die‐ lectric measurement methods, especially the broadband spectroscopic techniques. These methods enable fast, selective and non-destructive measurements using portable meters and sensors that can be applied in real time testing during production processes and monitoring of storage of various agricultural materials and food products. On the other hand, there are several significant obstacles hampering the development of effective dielectric techniques for determination of moisture content and related material properties. The main difficulties lie in the necessity of performing basic research to understand water-involving physical and chemical processes at micro- and macroscopic scales, mechanisms of polarization and influ‐ ence of electromagnetic waves on studied materials, development of selective sensor techni‐

The amount of water in a given body may be described by the mass or volume of water rela‐ tive to the mass or volume of the whole moist object or just the appropriate dry mass (Kras‐ zewski, 2001; Hillel, 2004). On a wet basis, the mass water content of a body is equal to the mass of the water, *mw*, divided by the bulk mass of the moist body, *mb*, which is the sum of

The mass water content on a dry basis is defined as the ratio of the mass of water to the

*<sup>η</sup>* <sup>=</sup> *mw md*

*mb* , *mb* <sup>=</sup>*mw* <sup>+</sup> *md* (1)

(2)

of aquametry.

18 Advances in Agrophysical Research

may become a challenging endeavour.

ques and achieving the required accuracy.

**1.1. Physical fundamentals and definitions**

mass of the dry material

the mass of the water and the mass of the dry material, *md*

*<sup>ξ</sup>* <sup>=</sup> *mw*

$$
\Theta\_v = \frac{V\_w}{V\_b} \tag{3}
$$

where *Vw* is the volume of water contained in a given body and *Vb* is the bulk volume of this body. Knowing the bulk density of the tested material, *ρ<sup>b</sup>* =*mb* / *Vb* , and the density of water, *ρw*, the volumetric water content may be expressed by the mass water content calcu‐ lated on a wet basis as follows

$$
\Theta\_v = \xi \frac{\rho\_b}{\rho\_w} \tag{4}
$$

The total amount of water contained in a given body does not fully determine all of its mois‐ ture related properties. The structure and chemical composition of a given body can greatly influence the properties of contained water. The molecule of water, consisting of two hydro‐ gen atoms bound to an atom of oxygen, exhibits polar structure. It may be described as a regular tetrahedron, with the oxygen atom in the centre and the hydrogen atoms with parti‐ al positive charges in two corners. Free corners of the tetrahedron are occupied by two elec‐ tron orbitals. Effectively, though a water molecule is not electrically charged, it possesses an electrical dipole moment. Water molecules are thus enabled to form hydrogen bonds with each other and another compatible polar chemical groups.

Because of the unique properties of water molecules, generally it is possible to distinguish three states of water in a moist material (Hillel, 2004; Lewicki, 2004; Chen and Or, 2006):

A physical thermodynamic quantity describing the state of water in a given body (liquid or solid) is called the water activity coefficient, *aw* (Lewicki, 2004). It is defined as the ratio of the water vapour pressure in a given material, *p*, to the vapour pressure of pure free water, *p*0, at the same temperature and total pressure

$$a\_w = \frac{p}{p\_0} \tag{5}$$

**2. Measurement methods and equipment**

examinations.

*2.1.1. Selectivity*

To properly and comprehensively characterise the influence of water contained in a given object on the properties of the said object, several parameters must be determined. In case of agricultural materials and food products, the most important of those parameters are: water content (by mass or by volume), water activity/potential and in case of soils also sal‐ inity, oxygenation and temperature (Malicki, 1999).Soil, being a porous three-phase body comprising of various mineral particles of different size and composition (clay, silt and sand particles) with soil water and air filling the pores, containing a countless number of various chemical compounds and organic matter, like microorganisms, flora and fauna spe‐ cies, is surely one of the most complex and variable medium in Nature. The accurate meas‐ urement of physical properties of such materials is thus a difficult challenge. Many of the modern aquametry techniques, appropriate for the soil, are also suitable for other materi‐ als like grain and food products, which are not as complex as soil. Therefore, the measure‐ ment methods and equipment described in this section will pertain mostly to soil water

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 21

From the agrophysical point of view, determining the status of water in soil and other po‐ rous materials is extremely important because each phenomenon and process taking place in such medium depends on its water-related properties (Blahovec, 2011). To achieve this goal, various methods and techniques have been developed, including sampling, non-de‐

The measurement of physical quantities is rarely direct, that is the value of a quantity in question is usually inferred from another quantity or quantities determined during the measurement process. For example, soil water content may be determined from measure‐ ments of mass of the moist and dry sample, electrical resistance or capacity, neutron scatter‐ ing, gamma-ray absorption or dielectric permittivity of the soil, depending on the applied measurement technique. The conversion function between the intermediary and the target quantities is called the calibration function. The critical issue in the selection of the measure‐ ment method is its selectivity, that is the lack of influence on the final result from factors other than the desired quantity. Good selectivity enables the usage of general calibrations,

The physical quantity enabling selective determination of soil water content in several mod‐ ern measurement techniques is dielectric permittivity. The relative dielectric permittivity of water for frequencies of the electric field below the relaxation frequency of 18 GHz is equal to about 80, while for the soil solid phase its value is of about 4 – 6. Therefore, the dielectric permittivity of soil is strongly dependent on the water content. The influence of the temper‐

structive proximal and remote sensing, automatic monitoring systems, etc.

**2.1. Common issues of water content measurement techniques**

valid for many types of soil and independent of local conditions.

Water activity is especially useful in food industries, in processing technology and to assess food safety. The water activity is greatly affected by the amount of solute molecules and their interaction with water. For example, the more of the water molecules are bounded by the solute molecules, the lower the *aw* is. The proliferation of microorganisms, causing spoil‐ age of food, depends on the value of the water activity. For given microbial species, there is an inhibiting value of *aw*, below which the proliferation is ceased. This is realised in many food preservation methods, such as freezing, salting and drying (Tapia et al., 2007).

To characterise the state of water in porous bodies such as soil, a quantity related to water activity, called water potential, *ϕ* , is defined as (Or and Wraith, 2002):

$$
\phi = \phi\_m + \phi\_o + \phi\_g + \phi\_p = RT \ln \frac{p}{p\_0} \tag{6}
$$

Here R = 8.31 JK-1mol-1 is the gas constant and *T* is the thermodynamic temperature. The definition above pertains to the total water potential, which is the sum of several terms:

To express water potential in terms of pressure, one needs to multiply it by water density. Because pressure of soil water may be lower than the atmospheric, matric potential may possess negative values. Disregarding the negative sign, water potential is called tension or suction. Water potential governs the direction of the water flow, that is water tends to flow from areas with high water potential (or low suction) towards areas, in which the potential is lower (or the suction higher). For example, when considering the soil-plant-atmosphere continuum, the differences in water potential between soil and roots determines the absorp‐ tion of water by plants.

## **2. Measurement methods and equipment**

To properly and comprehensively characterise the influence of water contained in a given object on the properties of the said object, several parameters must be determined. In case of agricultural materials and food products, the most important of those parameters are: water content (by mass or by volume), water activity/potential and in case of soils also sal‐ inity, oxygenation and temperature (Malicki, 1999).Soil, being a porous three-phase body comprising of various mineral particles of different size and composition (clay, silt and sand particles) with soil water and air filling the pores, containing a countless number of various chemical compounds and organic matter, like microorganisms, flora and fauna spe‐ cies, is surely one of the most complex and variable medium in Nature. The accurate meas‐ urement of physical properties of such materials is thus a difficult challenge. Many of the modern aquametry techniques, appropriate for the soil, are also suitable for other materi‐ als like grain and food products, which are not as complex as soil. Therefore, the measure‐ ment methods and equipment described in this section will pertain mostly to soil water examinations.

From the agrophysical point of view, determining the status of water in soil and other po‐ rous materials is extremely important because each phenomenon and process taking place in such medium depends on its water-related properties (Blahovec, 2011). To achieve this goal, various methods and techniques have been developed, including sampling, non-de‐ structive proximal and remote sensing, automatic monitoring systems, etc.

#### **2.1. Common issues of water content measurement techniques**

## *2.1.1. Selectivity*

A physical thermodynamic quantity describing the state of water in a given body (liquid or solid) is called the water activity coefficient, *aw* (Lewicki, 2004). It is defined as the ratio of the water vapour pressure in a given material, *p*, to the vapour pressure of pure free water,

Water activity is especially useful in food industries, in processing technology and to assess food safety. The water activity is greatly affected by the amount of solute molecules and their interaction with water. For example, the more of the water molecules are bounded by the solute molecules, the lower the *aw* is. The proliferation of microorganisms, causing spoil‐ age of food, depends on the value of the water activity. For given microbial species, there is an inhibiting value of *aw*, below which the proliferation is ceased. This is realised in many

To characterise the state of water in porous bodies such as soil, a quantity related to water

Here R = 8.31 JK-1mol-1 is the gas constant and *T* is the thermodynamic temperature. The definition above pertains to the total water potential, which is the sum of several terms:

**•** matric potential, denoted *ϕm*, which depends on the capillary pressure and the adsorption

**•** osmotic pressure potential, *ϕo*, describing the influence of solutes on the state of water;

**•** gravitational potential, *ϕg*, arising from the gravitational force being exerted on the water

**•** pressure potential, *ϕp*, defined as the hydrostatic pressure exerted by unsupported water

To express water potential in terms of pressure, one needs to multiply it by water density. Because pressure of soil water may be lower than the atmospheric, matric potential may possess negative values. Disregarding the negative sign, water potential is called tension or suction. Water potential governs the direction of the water flow, that is water tends to flow from areas with high water potential (or low suction) towards areas, in which the potential is lower (or the suction higher). For example, when considering the soil-plant-atmosphere continuum, the differences in water potential between soil and roots determines the absorp‐

this term is often neglected for porous bodies with no diffusion barriers,

<sup>+</sup> *<sup>ϕ</sup><sup>p</sup>* <sup>=</sup>*RT* ln *<sup>p</sup>*

*p*0

(5)

(6)

*aw* <sup>=</sup> *<sup>p</sup> p*0

food preservation methods, such as freezing, salting and drying (Tapia et al., 2007).

activity, called water potential, *ϕ* , is defined as (Or and Wraith, 2002):

*ϕ* =*ϕ<sup>m</sup>* + *ϕ<sup>o</sup>* + *ϕ<sup>g</sup>*

*p*0, at the same temperature and total pressure

20 Advances in Agrophysical Research

of water on the surfaces of solid particles,

(i.e., saturating the soil) overlying a point of interest.

confined in a given porous body,

tion of water by plants.

The measurement of physical quantities is rarely direct, that is the value of a quantity in question is usually inferred from another quantity or quantities determined during the measurement process. For example, soil water content may be determined from measure‐ ments of mass of the moist and dry sample, electrical resistance or capacity, neutron scatter‐ ing, gamma-ray absorption or dielectric permittivity of the soil, depending on the applied measurement technique. The conversion function between the intermediary and the target quantities is called the calibration function. The critical issue in the selection of the measure‐ ment method is its selectivity, that is the lack of influence on the final result from factors other than the desired quantity. Good selectivity enables the usage of general calibrations, valid for many types of soil and independent of local conditions.

The physical quantity enabling selective determination of soil water content in several mod‐ ern measurement techniques is dielectric permittivity. The relative dielectric permittivity of water for frequencies of the electric field below the relaxation frequency of 18 GHz is equal to about 80, while for the soil solid phase its value is of about 4 – 6. Therefore, the dielectric permittivity of soil is strongly dependent on the water content. The influence of the temper‐ ature in many cases may be neglected (Skierucha, 2009). The salinity of the soil may also in‐ terfere with the water content measurement, however its influence is negligible for the electric field frequencies of the order of 400 MHz and higher (Skierucha and Wilczek, 2010). The dielectric measurement methods, described in detail in section 2.3.2, are therefore high‐ ly selective and give reliable results for various field conditions.

**Name of the measurement method**

> TDR (time domain reflectometry)

FDR (frequency domain reflectometry)

Neutron scattering

Electrical resistance blocks

2011)

**Directly measured quantity, physical principle, soil**

Velocity of propagation of the electromagnetic wave (step or needle pulse) along the metallic parallel or coaxial waveguide (TDR probe) fully inserted into the soil. It is very well correlated with the real part of the soil complex dielectric permittivity as well as the amount of water in soil (Topp et al., 1980; Noborio et al., 1999).

Attenuation of the electromagnetic wave during its travel in the TDR probe, which results mainly from the soil electrical conductivity dependent ion conduction. Signal attenuation is correlated with the soil bulk electrical conductivity and soil salinity (electrical conductivity of soil extract) (Malicki and Walczak, 1999;

Phase shift (dependent on soil bulk dielectric

permittivity) and amplitude attenuation (dependent on soil salinity) of an electrical signal a probe inserted into the soil treated as a lossy capacitor. Measurement is done in a single frequency generated by the internal probe oscillator (50-150 MHz) (Veldkamp and O'Brien,

Number slow neutrons that are produced from the collision of fast neutrons with hydrogen molecules in soil, which is linearly related to the soil volumetric water content. Fast neutron generator and the counter are

transducer in a water filled tube connected with soil matrix by a porous cap. The measured physical quantity is a matrix potential of soil water, which is an basic element of the total potential of water in the soil

Electrical resistance, measured with an alternating current bridge (usually ≈ 1000 Hz) of electrodes encased in some type of porous material (gypsum, nylon fabric, fiberglass) that within about two days will reach a quasi-equilibrium state with the soil. This method determines soil water content and water potential as a function of electrical resistance (Spaans and Baker,

**Table 1.** Selection of the most popular non-destructive soil water status measurement methods, from (Skierucha,

installed in the vertical access tube for the measurements in different layers of soil (Evett and **Remarks**

geometry.

Commonly recognized alternative for the thermogravimetric method, instruments are still very expensive, usually no site calibration required.

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 23

Not applicable for very saline soils and long probe rods, limited accuracy caused by the possible change of the TDR probe

Requires soil site calibration, probes and meters are commercially available and cheaper than TDR

instrumentation, low power consumption as compared to

Limited range of work (down to

requires frequent servicing (air bubbles),in drought conditions water moves from the tensiometer to the soil.

Sensitive to soil salinity and temperature, requires soil specific calibration, very economic and field installations can work for several years, supplementary to tensiometers in the range up to

TDR technique.

Requires soil site calibration ,precise but expensive, additional cost with special licensing, operator training, handling, radiation materials waste disposal, health

hazard.

about -85 kPa),

**property measured and references**

Robinson et al., 2003).

2000).

Steiner, 1995).

Tensiometry Suction force or pressure exerted on a pressure

1992; Hillel, 2004).

(Mullins, 2001; Sisson et al., 2002).

Salinity of the soil may also be determined by electrical measurements. Salts dissolved in the soil water are the sources of ions, which enable the electric current conduction. Therefore, the soil electrical conductivity may be used as a salinity measure. Electrical conductivity is highly dependent not only on the concentration of ions, but also on temperature and water content. However, there are integrated dielectric sensors that enable simultaneous measure‐ ments of soil moisture, temperature and electrical conductivity.

#### *2.1.2. Resolution and sampling*

In case of inhomogeneous medium, the volume of the sample, on which the measurement is performed, may influence the final result. Because of the spatial and temporal variability of the soil, the measured values may differ even for points in proximity to each other.

Soil water content may be examined at a point, field, catchment, country or global scale. The spatial and temporal resolution and coverage of the measurements depend on the measure‐ ment and monitoring technique, selection of which is dependent on the purpose of the measurements. For example, satellite sensing provides global coverage with spatial resolu‐ tion of many kilometres, while proximal techniques give soil moisture values close to a point scale, with the spatial and temporal coverage limited by the number of monitoring sta‐ tions and the chosen time schedule for the measurements (Vereecken et al., 2008; Skierucha and Wilczek, 2010).

Several soil water content measurement techniques, like the thermogravimetric method de‐ scribed in section 2.2, require acquisition of traditional samples. The process is usually dis‐ ruptive to the surroundings and may disturb the sample itself. The extraction, transport and processing of the sample may introduce errors, which may be reduced by increasing the number and volume of taken samples. Such measurement methods are usually laborious and time-consuming, which makes them unsuitable for monitoring applications.

#### *2.1.3. Non-destructive measurements*

There is a number of measurement techniques which do not require extraction of samples and provide means for non-destructive or even non-invasive testing.

Non-destructive measurement methods do not disturb the sample, enabling repetitive ex‐ aminations of the same object. However, installation of probes and measurement stations in the soil may still be required. The advantage is that after the initial disturbance during the installation, the act of measurement do not affect the tested sample nor its surroundings. Such techniques are therefore suitable even for long-term monitoring purposes.

ature in many cases may be neglected (Skierucha, 2009). The salinity of the soil may also in‐ terfere with the water content measurement, however its influence is negligible for the electric field frequencies of the order of 400 MHz and higher (Skierucha and Wilczek, 2010). The dielectric measurement methods, described in detail in section 2.3.2, are therefore high‐

Salinity of the soil may also be determined by electrical measurements. Salts dissolved in the soil water are the sources of ions, which enable the electric current conduction. Therefore, the soil electrical conductivity may be used as a salinity measure. Electrical conductivity is highly dependent not only on the concentration of ions, but also on temperature and water content. However, there are integrated dielectric sensors that enable simultaneous measure‐

In case of inhomogeneous medium, the volume of the sample, on which the measurement is performed, may influence the final result. Because of the spatial and temporal variability of

Soil water content may be examined at a point, field, catchment, country or global scale. The spatial and temporal resolution and coverage of the measurements depend on the measure‐ ment and monitoring technique, selection of which is dependent on the purpose of the measurements. For example, satellite sensing provides global coverage with spatial resolu‐ tion of many kilometres, while proximal techniques give soil moisture values close to a point scale, with the spatial and temporal coverage limited by the number of monitoring sta‐ tions and the chosen time schedule for the measurements (Vereecken et al., 2008; Skierucha

Several soil water content measurement techniques, like the thermogravimetric method de‐ scribed in section 2.2, require acquisition of traditional samples. The process is usually dis‐ ruptive to the surroundings and may disturb the sample itself. The extraction, transport and processing of the sample may introduce errors, which may be reduced by increasing the number and volume of taken samples. Such measurement methods are usually laborious

There is a number of measurement techniques which do not require extraction of samples

Non-destructive measurement methods do not disturb the sample, enabling repetitive ex‐ aminations of the same object. However, installation of probes and measurement stations in the soil may still be required. The advantage is that after the initial disturbance during the installation, the act of measurement do not affect the tested sample nor its surroundings.

and time-consuming, which makes them unsuitable for monitoring applications.

Such techniques are therefore suitable even for long-term monitoring purposes.

and provide means for non-destructive or even non-invasive testing.

the soil, the measured values may differ even for points in proximity to each other.

ly selective and give reliable results for various field conditions.

ments of soil moisture, temperature and electrical conductivity.

*2.1.2. Resolution and sampling*

22 Advances in Agrophysical Research

and Wilczek, 2010).

*2.1.3. Non-destructive measurements*

**Table 1.** Selection of the most popular non-destructive soil water status measurement methods, from (Skierucha, 2011)

On the other hand, non-invasive techniques do not introduce any disturbance of the tested material. Particularly, they do not use any probes which must be installed in the measure‐ ment site. Non-invasive methods include techniques such as airborne and satellite remote sensing (Jackson et al., 1996) or near infra-red reflectance spectroscopy (NIRS) (Cécillon et al., 2009). Remote techniques usually examine only the topsoil and require ground measure‐ ments for the proper calibration. However, they are irreplaceable for the monitoring of the soil properties on a global scale.

by placing in an oven at temperature of 105°C for 24 hours (Hillel, 2004). However, this is still an arbitrary standard. It is difficult to completely dry a material containing microscopic pores and solid particles which easily adsorb water. Some soils, especially those containing much clay, may still hold some water even after the standard drying. On the other hand, some soils may contain many compounds which tend to decompose and evaporate along with water, while the sample is in the oven. The evaporation of other compounds beside

Another source of error in the moisture content measurement by the thermogravimetric method is the extraction of a sample and its transport to the laboratory, where usually the oven is located. Each disturbance of the sample during this process may cause errors. Fur‐ thermore, in this method the sample is irreversibly destroyed during the drying process, al‐

There exist a method of drying alternative to the oven, in which the sample is placed in a container and impregnated with alcohol (Hillel, 2004). The alcohol is then burned off, what

The thermogravimetric method, despite being destructive, laborious, time-consuming, prone to errors and completely impractical for monitoring purposes, is commonly regarded as a reference method. Most importantly, it is used as a calibration standard for other mois‐

One of the most important chemical method of water content measurement is the Karl Fischer titration(Isengard, 2001). It is regarded as a reference method for determining the

In the volumetric variation of this technique, a sample of tested material, i.e. the analyte, is placed in a titration cell along with the working medium and the titrant solution. The chemi‐ cal components added to the analyte are: alcohol (ROH, usually methanol), sulphur dioxide (SO2), a base (B, usually imidazole) and iodine (I2). The overall reaction that occurs in the

In the net reaction, one mole of iodine is consumed per one mole of water from the analyte. The amount of water is therefore measured by the consumption of iodine. In the coulometric variation of this method, iodine is not added in the solution, but it is produced in the cell

The end-point of the reaction is detected through electrochemical means. There are two plat‐ inum electrodes placed in the titration cell. In the so called bipotentiometric technique, a constant current is maintained on the electrodes and the voltage is monitored. In the biam‐ perometric variation, the voltage is kept constant and the current is measured. When all the

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 25

3B <sup>+</sup> ROH <sup>+</sup> SO2 <sup>+</sup> I2 <sup>+</sup> H2O→3BH<sup>+</sup> <sup>+</sup> ROSO3

water causes overestimation of the initial water content of the sample.

causes the evaporation of water. This method may be used in the field.

lowing only one measurement of a given sample.

ture measurement techniques.

moisture content of food products.

*2.2.2. Karl Fischer titration*

titration cell is as follows:

from iodide by anodic oxidation.

Non-destructive measurement methods have been adapted by agrophysics from various branches of science and industry. Therefore, the physical principles of those techniques vary greatly, from optical to electrical and nuclear methods. Despite the underlying measurement principle, the sensor device suitable for non-destructive and repetitive testing should pos‐ sess several universal features, such as a data-logging option, a power supply enabling longterm operation without recharging and the communication capability for the remote configuration and transferring of the measurement results to the user. An overview of vari‐ ous non-destructive soil water measurement methods is presented in Table 1. The measur‐ ing principle of each technique is briefly described, along with the most important advantages and limitations.

Because the determination of soil water status requires measurement of several parameters, the construction of integrated sensors, which measure several soil properties at the same time and on the same sample volume, becomes increasingly popular. For example, TDR and FDR methods enable the development of the soil water content and soil salinity measure‐ ment device, with the possibility of an addition of a temperature sensor (Skierucha et al., 2006).

#### **2.2. Direct methods of water content measurement**

#### *2.2.1. Thermogravimetric method*

The traditional and standard water content measurement technique, called the thermogra‐ vimetric method, is based on a very simple concept of weighting a sample of a moist mate‐ rial, drying it and then weighting again. The difference between the mass of the moist and the dry material, equal to the mass of water evaporated from the original sample, divided by the mass of the dry material (assuming all of the water evaporated during the drying process), is an exact definition of mass water content on a dry basis (Equation 2). This quantity is also called gravimetric water content. Volumetric water content, when re‐ quired, may be then easily calculated from the mass water content, according to relations presented in section 1.1.

However, the practical application of the thermogravimetric method is not so simple. First, a sample of a material under test needs to be collected. In case of soil testing, this process is invasive and disruptive to the soil profile and its surroundings. To achieve comparative re‐ sults, the process of drying needs to be standardised. The temperature and time length of the drying should be adjusted to the specifics of a given material. For soils, a sample is dried by placing in an oven at temperature of 105°C for 24 hours (Hillel, 2004). However, this is still an arbitrary standard. It is difficult to completely dry a material containing microscopic pores and solid particles which easily adsorb water. Some soils, especially those containing much clay, may still hold some water even after the standard drying. On the other hand, some soils may contain many compounds which tend to decompose and evaporate along with water, while the sample is in the oven. The evaporation of other compounds beside water causes overestimation of the initial water content of the sample.

Another source of error in the moisture content measurement by the thermogravimetric method is the extraction of a sample and its transport to the laboratory, where usually the oven is located. Each disturbance of the sample during this process may cause errors. Fur‐ thermore, in this method the sample is irreversibly destroyed during the drying process, al‐ lowing only one measurement of a given sample.

There exist a method of drying alternative to the oven, in which the sample is placed in a container and impregnated with alcohol (Hillel, 2004). The alcohol is then burned off, what causes the evaporation of water. This method may be used in the field.

The thermogravimetric method, despite being destructive, laborious, time-consuming, prone to errors and completely impractical for monitoring purposes, is commonly regarded as a reference method. Most importantly, it is used as a calibration standard for other mois‐ ture measurement techniques.

#### *2.2.2. Karl Fischer titration*

On the other hand, non-invasive techniques do not introduce any disturbance of the tested material. Particularly, they do not use any probes which must be installed in the measure‐ ment site. Non-invasive methods include techniques such as airborne and satellite remote sensing (Jackson et al., 1996) or near infra-red reflectance spectroscopy (NIRS) (Cécillon et al., 2009). Remote techniques usually examine only the topsoil and require ground measure‐ ments for the proper calibration. However, they are irreplaceable for the monitoring of the

Non-destructive measurement methods have been adapted by agrophysics from various branches of science and industry. Therefore, the physical principles of those techniques vary greatly, from optical to electrical and nuclear methods. Despite the underlying measurement principle, the sensor device suitable for non-destructive and repetitive testing should pos‐ sess several universal features, such as a data-logging option, a power supply enabling longterm operation without recharging and the communication capability for the remote configuration and transferring of the measurement results to the user. An overview of vari‐ ous non-destructive soil water measurement methods is presented in Table 1. The measur‐ ing principle of each technique is briefly described, along with the most important

Because the determination of soil water status requires measurement of several parameters, the construction of integrated sensors, which measure several soil properties at the same time and on the same sample volume, becomes increasingly popular. For example, TDR and FDR methods enable the development of the soil water content and soil salinity measure‐ ment device, with the possibility of an addition of a temperature sensor (Skierucha et al.,

The traditional and standard water content measurement technique, called the thermogra‐ vimetric method, is based on a very simple concept of weighting a sample of a moist mate‐ rial, drying it and then weighting again. The difference between the mass of the moist and the dry material, equal to the mass of water evaporated from the original sample, divided by the mass of the dry material (assuming all of the water evaporated during the drying process), is an exact definition of mass water content on a dry basis (Equation 2). This quantity is also called gravimetric water content. Volumetric water content, when re‐ quired, may be then easily calculated from the mass water content, according to relations

However, the practical application of the thermogravimetric method is not so simple. First, a sample of a material under test needs to be collected. In case of soil testing, this process is invasive and disruptive to the soil profile and its surroundings. To achieve comparative re‐ sults, the process of drying needs to be standardised. The temperature and time length of the drying should be adjusted to the specifics of a given material. For soils, a sample is dried

soil properties on a global scale.

24 Advances in Agrophysical Research

advantages and limitations.

*2.2.1. Thermogravimetric method*

presented in section 1.1.

**2.2. Direct methods of water content measurement**

2006).

One of the most important chemical method of water content measurement is the Karl Fischer titration(Isengard, 2001). It is regarded as a reference method for determining the moisture content of food products.

In the volumetric variation of this technique, a sample of tested material, i.e. the analyte, is placed in a titration cell along with the working medium and the titrant solution. The chemi‐ cal components added to the analyte are: alcohol (ROH, usually methanol), sulphur dioxide (SO2), a base (B, usually imidazole) and iodine (I2). The overall reaction that occurs in the titration cell is as follows:

$$\rm{\rm{\tiny{3B}+ROH}+SO\_2} + \rm{I}\_2 + \rm{I}\_2\rm{O} \rightarrow \rm{\rm{3BH}^\*} + \rm{ROSO\_3^\*} + \rm{2I^\*} \tag{7}$$

In the net reaction, one mole of iodine is consumed per one mole of water from the analyte. The amount of water is therefore measured by the consumption of iodine. In the coulometric variation of this method, iodine is not added in the solution, but it is produced in the cell from iodide by anodic oxidation.

The end-point of the reaction is detected through electrochemical means. There are two plat‐ inum electrodes placed in the titration cell. In the so called bipotentiometric technique, a constant current is maintained on the electrodes and the voltage is monitored. In the biam‐ perometric variation, the voltage is kept constant and the current is measured. When all the water is consumed, the redox reactions between iodine and iodide ions occur, what causes an abrupt rise of current (biamperometric technique) or a sudden drop of voltage (bipoten‐ tiometric technique). The determination of the end-point of the reaction therefore allows for the calculation of the total amount of water in the sample. The end-point is usually amended by a stop delay time correction, accounting for water that is held by the sample and not im‐ mediately available for the reaction.

is naturally water. The thermalized neutrons are then detected by the probe. The number of counts of the slow neutrons is approximately proportional to the volumetric water content

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 27

With proper usage, this moisture content measurement method is very accurate. However, to test the water content of the top layer of the soil requires special precautions preventing escape of fast neutrons to the atmosphere. The main drawbacks of this technique are: the ra‐ diation hazard, expensive equipment, personnel training, low spatial resolution and the ne‐

Recently, a new remote sensing technique based on the scattering of the cosmic-ray neutrons has been proposed (Zreda et al., 2008). Cosmic rays, consisting mainly of protons, collide with atomic nuclei in atmosphere, creating cascades of secondary particles, including neu‐ trons. Those neutrons may then penetrate soil and scatter, the process of which depends on the soil water content, as described above. Some of these neutrons may diffuse back to the atmosphere, where they may be detected by remote sensors placed several metres above the ground. The measurement results are integrated over large areas (approx. 670 m in diame‐ ter), therefore they may be used as an intermediate between on site and satellite sensing (Dorigo et al., 2011). This moisture sensing technique is non-invasive and does not require usage of any radioactive or otherwise hazardous elements. Furthermore, it is suitable for

Dielectric properties or permittivity of agricultural products are of interest for several rea‐ sons. They include the sensing of moisture content in these products through its correlation with the dielectric properties of cereal grain and oilseed crops, the influence of permittivity on the dielectric heating of product at microwave or lower radio frequencies, and the poten‐ tial use of dielectric permittivity for sensing quality factors other than moisture content (Nel‐

The subject of interest for electromagnetic aquametry is analysing solids of different form and structure, as well as liquids containing water, for identification of their properties when placed in electromagnetic fields of radio and microwave frequencies (attenuation, reflection, phase angle, shift of resonant frequency, etc.). The physical principle of the dielectric mois‐ ture content measurement methods is based on the high value of relative dielectric permit‐ tivity of free water (about 80 at room temperature) with respect to air (equal to 1) and other

Microwave aquametry, as a branch of electromagnetic aquametry (Kraszewski, 2005) of ma‐ terials' dielectric properties, applies high measurement frequencies, where only dipole po‐ larization of free and bound water particles is active. The measurement techniques of microwave aquametry provide information about free water content. The following advan‐

**a.** contrary to lower frequencies, the conductivity effects on material properties can be ne‐

materials (for example, dry soil has relative dielectric permittivity of about 4 – 6).

tages of microwave aquametry were obvious since the early experiments:

in the soil.

cessity of the site specific calibration.

long-term environmental monitoring purposes.

*2.3.2. Dielectric methods – electromagnetic aquametry*

son, 2005; Skierucha et al., 2012).

glected,

The Karl Fischer titration is very accurate and can determine even extremely small amounts of water. However, the main disadvantage is that all the water in the sample should be made available for the reaction, which is sometimes difficult to achieve, for example in case of insoluble materials. This measurement method is also destructive, but fortunately it does not require large samples.

#### **2.3. Indirect methods of moisture content measurement**

Direct methods of moisture content determination in soils and biomaterials usually are time consuming, require laboratory equipment and are not practical for use in automatic systems to monitor environmental conditions and to control industrial technological processes. Due to spatial (from water volume fraction in soil micropores to water balance in continents) and temporal diversity (from milliseconds when analyzing water fluxes to days or weeks in weather prediction) of moisture content in analyzed objects, selectivity requirements and cost of the applied measurement equipment, the indirect methods of moisture content meas‐ urement require interdisciplinary approach that links deep knowledge about physical, chemical and biological processes in tested materials and engineering invention in designing appropriate sensors and meters.

The selection of moisture content measurement techniques presented below is not complete, it only covers representative or the most common ones.

#### *2.3.1. Neutron scattering*

One of the most accurate non-destructive water content measurement method involves de‐ tection of scattered neutrons emitted from a radioactive source placed within the soil (Hillel, 2004; Robinson et al., 2008). Although it requires installation of an access tube with the neu‐ tron source and the probe, which is invasive, the method allows for repetitive measure‐ ments of the site without further disturbances.

The neutron moisture meter commonly uses mixtures of radium and beryllium or americi‐ um and beryllium as the source of radiation. Radioactive elements emit into the soil gamma radiation and "fast neutrons", that is neutrons with high energy up to 15 MeV. The neutrons then collide with atomic nuclei present in the soil, scatter and lose energy, until they ap‐ proach a typical energy of particles at a given temperature, that is of about 0.03 eV. Neu‐ trons with such energy are called "thermalized" or "slow". Then they are finally absorbed by the atomic nuclei in soil. It happens that the neutrons are most effectively scattered through collisions with nuclei which mass is similar to their own, that is with protons, con‐ stituting the nuclei of hydrogen atoms. The most prevalent source of hydrogen atoms in soil is naturally water. The thermalized neutrons are then detected by the probe. The number of counts of the slow neutrons is approximately proportional to the volumetric water content in the soil.

With proper usage, this moisture content measurement method is very accurate. However, to test the water content of the top layer of the soil requires special precautions preventing escape of fast neutrons to the atmosphere. The main drawbacks of this technique are: the ra‐ diation hazard, expensive equipment, personnel training, low spatial resolution and the ne‐ cessity of the site specific calibration.

Recently, a new remote sensing technique based on the scattering of the cosmic-ray neutrons has been proposed (Zreda et al., 2008). Cosmic rays, consisting mainly of protons, collide with atomic nuclei in atmosphere, creating cascades of secondary particles, including neu‐ trons. Those neutrons may then penetrate soil and scatter, the process of which depends on the soil water content, as described above. Some of these neutrons may diffuse back to the atmosphere, where they may be detected by remote sensors placed several metres above the ground. The measurement results are integrated over large areas (approx. 670 m in diame‐ ter), therefore they may be used as an intermediate between on site and satellite sensing (Dorigo et al., 2011). This moisture sensing technique is non-invasive and does not require usage of any radioactive or otherwise hazardous elements. Furthermore, it is suitable for long-term environmental monitoring purposes.

#### *2.3.2. Dielectric methods – electromagnetic aquametry*

water is consumed, the redox reactions between iodine and iodide ions occur, what causes an abrupt rise of current (biamperometric technique) or a sudden drop of voltage (bipoten‐ tiometric technique). The determination of the end-point of the reaction therefore allows for the calculation of the total amount of water in the sample. The end-point is usually amended by a stop delay time correction, accounting for water that is held by the sample and not im‐

The Karl Fischer titration is very accurate and can determine even extremely small amounts of water. However, the main disadvantage is that all the water in the sample should be made available for the reaction, which is sometimes difficult to achieve, for example in case of insoluble materials. This measurement method is also destructive, but fortunately it does

Direct methods of moisture content determination in soils and biomaterials usually are time consuming, require laboratory equipment and are not practical for use in automatic systems to monitor environmental conditions and to control industrial technological processes. Due to spatial (from water volume fraction in soil micropores to water balance in continents) and temporal diversity (from milliseconds when analyzing water fluxes to days or weeks in weather prediction) of moisture content in analyzed objects, selectivity requirements and cost of the applied measurement equipment, the indirect methods of moisture content meas‐ urement require interdisciplinary approach that links deep knowledge about physical, chemical and biological processes in tested materials and engineering invention in designing

The selection of moisture content measurement techniques presented below is not complete,

One of the most accurate non-destructive water content measurement method involves de‐ tection of scattered neutrons emitted from a radioactive source placed within the soil (Hillel, 2004; Robinson et al., 2008). Although it requires installation of an access tube with the neu‐ tron source and the probe, which is invasive, the method allows for repetitive measure‐

The neutron moisture meter commonly uses mixtures of radium and beryllium or americi‐ um and beryllium as the source of radiation. Radioactive elements emit into the soil gamma radiation and "fast neutrons", that is neutrons with high energy up to 15 MeV. The neutrons then collide with atomic nuclei present in the soil, scatter and lose energy, until they ap‐ proach a typical energy of particles at a given temperature, that is of about 0.03 eV. Neu‐ trons with such energy are called "thermalized" or "slow". Then they are finally absorbed by the atomic nuclei in soil. It happens that the neutrons are most effectively scattered through collisions with nuclei which mass is similar to their own, that is with protons, con‐ stituting the nuclei of hydrogen atoms. The most prevalent source of hydrogen atoms in soil

mediately available for the reaction.

**2.3. Indirect methods of moisture content measurement**

it only covers representative or the most common ones.

ments of the site without further disturbances.

not require large samples.

26 Advances in Agrophysical Research

appropriate sensors and meters.

*2.3.1. Neutron scattering*

Dielectric properties or permittivity of agricultural products are of interest for several rea‐ sons. They include the sensing of moisture content in these products through its correlation with the dielectric properties of cereal grain and oilseed crops, the influence of permittivity on the dielectric heating of product at microwave or lower radio frequencies, and the poten‐ tial use of dielectric permittivity for sensing quality factors other than moisture content (Nel‐ son, 2005; Skierucha et al., 2012).

The subject of interest for electromagnetic aquametry is analysing solids of different form and structure, as well as liquids containing water, for identification of their properties when placed in electromagnetic fields of radio and microwave frequencies (attenuation, reflection, phase angle, shift of resonant frequency, etc.). The physical principle of the dielectric mois‐ ture content measurement methods is based on the high value of relative dielectric permit‐ tivity of free water (about 80 at room temperature) with respect to air (equal to 1) and other materials (for example, dry soil has relative dielectric permittivity of about 4 – 6).

Microwave aquametry, as a branch of electromagnetic aquametry (Kraszewski, 2005) of ma‐ terials' dielectric properties, applies high measurement frequencies, where only dipole po‐ larization of free and bound water particles is active. The measurement techniques of microwave aquametry provide information about free water content. The following advan‐ tages of microwave aquametry were obvious since the early experiments:

**a.** contrary to lower frequencies, the conductivity effects on material properties can be ne‐ glected,

**b.** penetration depth is much larger than that of infrared radiation and permits the prob‐ ing of a significant volume of material being transported on a conveyor or in a pipe,

the surfaces between different materials, from which the cell is formed (Markx and Davey, 1999). The α-dispersion is due to the tangential flow of ions across cell surfaces, the β-dis‐ persion results from the build-up of charge at cell membranes due to the Maxwell–Wagner effect, the δ-dispersion is produced by the rotation of macromolecular side-chains and bound water, and the γ-dispersion is due to the dipolar rotation of small molecules, particu‐ larly water. The low frequency polarization masks the bound water and free water disper‐ sion effects. Therefore, the use of microwaves in the analysis of electromagnetic field

The most common dielectric techniques for determination of moisture content in soils and biomaterials use capacitance sensors. They usually work in low frequencies up to 150 MHz. A sensor is in a form of a capacitor of parameters modified by dielectric permittivity and electrical conductivity of the surrounding material. The representative probes applied for the measurement of soil moisture and electrical conductivity are: Theta Probe or ECHO moisture sensor with performance and characteristics described broadly in literature (Li et al., 2005; Kizito et al., 2008). Capacitance sensors are not expensive and when equipped with wireless communication and scattered on large areas, they are especially useful in monitor‐ ing soil moisture for environmental and irrigation scheduling (Zhang et al., 2011), although

Radio frequency and microwaves techniques include: reflection measurements with the use of an open-ended coaxial probe (Skierucha et al., 2004; Agilent, 2006), transmission measure‐ ments with the use of materials' samples placed inside transmission lines and microwave

The complex relative permittivity *ε \** of a material can be expressed in the following complex

poles rotation,*<sup>σ</sup>* (S <sup>m</sup>-1) is the ionic conductivity, *<sup>ω</sup>* (rad <sup>s</sup>-1) is the angular frequency and *ε*0 is the permittivity of free space or vacuum (8.854 10-12 F m-1), and *j* = -1. Mechanisms that con‐ tribute to the dielectric loss in heterogeneous mixtures include polar, electronic, atomic and Maxwell–Wagner responses. Aquametry measurements at RF and microwave frequencies are of practical importance and they are currently used for applications in food processing (Venkatesh and Raghavan, 2004), food treatment (Marra et al., 2009) and quality determina‐

<sup>+</sup> *<sup>σ</sup>*

is referred to as the dielectric constantand represents stored energy when

''

*<sup>ε</sup>*0*<sup>ω</sup>* ) (8)

stands for the contribution due to di‐

, which is the imaginary

Aquametry in Agrophysics http://dx.doi.org/10.5772/52505 29

interactions with soils and biomaterials is recommended.

they are not so accurate as TDR sensors (Evett et al., 2012).

*ε* \* =*ε* ' - *jε* '' =*ε* ' - *j*(*ε<sup>d</sup>* ''

part, influences energy absorption and attenuation, *ε<sup>d</sup>*

the material is exposed to anelectric field, while the loss factor *ε ''*

tion of biomaterials and food products (Wang, 2003; Sosa-Morales et al., 2010).

*<IP_ADDRESS>. Frequency domain sensors*

resonators (King, 2000).

form:

The real part *ε '*

Since heterogeneous systems have interfaces where the materials of different electrical prop‐ erties contact each other, producing interfacial polarization that is due to the build-up of charge on the interfaces and causing current flow. Through introduction of external electri‐ cal field of variable frequency, it is possible to observe changes of the complex dielectric per‐ mittivity of the examined heterogenic material (electrical dispersion). The real part of the permittivity describes the ability of the material to polarize the internal electrical dipoles and charge carriers, and its imaginary part describes the energy loss of the electric field (die‐ lectric loss and conductivity loss). These changes are characteristic for each analysed materi‐ al because of its unique physical and chemical properties. The dielectric relaxation due to interfacial polarization provides information on the heterogeneous structure and the electri‐ cal properties of the constituent components.

**Figure 1.** Idealized spectrum of the real part of the complex dielectric permittivity of cell suspensions and tissues. The step changes in dielectric permittivity are called dispersions and are due to the loss of particular polarization processes as frequency increases (from (Markx and Davey, 1999))

For most substances the electrical permittivity and conductivity are constant only for a limit‐ ed range of frequencies. Within increasing frequency permittivity decreases, while the con‐ ductivity increases abruptly. These abrupt changes are called dispersions, and each of them represents a specific process of polarization. Biological materials are characterized by high dispersion, especially at low frequencies (Figure 1). It is caused by interfacial polarization on the surfaces between different materials, from which the cell is formed (Markx and Davey, 1999). The α-dispersion is due to the tangential flow of ions across cell surfaces, the β-dis‐ persion results from the build-up of charge at cell membranes due to the Maxwell–Wagner effect, the δ-dispersion is produced by the rotation of macromolecular side-chains and bound water, and the γ-dispersion is due to the dipolar rotation of small molecules, particu‐ larly water. The low frequency polarization masks the bound water and free water disper‐ sion effects. Therefore, the use of microwaves in the analysis of electromagnetic field interactions with soils and biomaterials is recommended.

#### *<IP_ADDRESS>. Frequency domain sensors*

**b.** penetration depth is much larger than that of infrared radiation and permits the prob‐ ing of a significant volume of material being transported on a conveyor or in a pipe, **c.** physical contact between the equipment and the material under test is not required, al‐

**d.** in contrast to infrared radiation, it is relatively insensitive to environmental conditions, thus dust and water vapour in industrial facilities do not affect the measurement, **e.** water reacts specifically with certain frequencies in the microwave region (relaxation)

**f.** contrary to chemical methods, it does not alter or contaminate the test material, thus the

Since heterogeneous systems have interfaces where the materials of different electrical prop‐ erties contact each other, producing interfacial polarization that is due to the build-up of charge on the interfaces and causing current flow. Through introduction of external electri‐ cal field of variable frequency, it is possible to observe changes of the complex dielectric per‐ mittivity of the examined heterogenic material (electrical dispersion). The real part of the permittivity describes the ability of the material to polarize the internal electrical dipoles and charge carriers, and its imaginary part describes the energy loss of the electric field (die‐ lectric loss and conductivity loss). These changes are characteristic for each analysed materi‐ al because of its unique physical and chemical properties. The dielectric relaxation due to interfacial polarization provides information on the heterogeneous structure and the electri‐

**Figure 1.** Idealized spectrum of the real part of the complex dielectric permittivity of cell suspensions and tissues. The step changes in dielectric permittivity are called dispersions and are due to the loss of particular polarization processes

For most substances the electrical permittivity and conductivity are constant only for a limit‐ ed range of frequencies. Within increasing frequency permittivity decreases, while the con‐ ductivity increases abruptly. These abrupt changes are called dispersions, and each of them represents a specific process of polarization. Biological materials are characterized by high dispersion, especially at low frequencies (Figure 1). It is caused by interfacial polarization on

lowing on-line continuous and remote moisture sensing,

allowing even small amounts of water to be detected.

measurement is non-destructive.

28 Advances in Agrophysical Research

cal properties of the constituent components.

as frequency increases (from (Markx and Davey, 1999))

The most common dielectric techniques for determination of moisture content in soils and biomaterials use capacitance sensors. They usually work in low frequencies up to 150 MHz. A sensor is in a form of a capacitor of parameters modified by dielectric permittivity and electrical conductivity of the surrounding material. The representative probes applied for the measurement of soil moisture and electrical conductivity are: Theta Probe or ECHO moisture sensor with performance and characteristics described broadly in literature (Li et al., 2005; Kizito et al., 2008). Capacitance sensors are not expensive and when equipped with wireless communication and scattered on large areas, they are especially useful in monitor‐ ing soil moisture for environmental and irrigation scheduling (Zhang et al., 2011), although they are not so accurate as TDR sensors (Evett et al., 2012).

Radio frequency and microwaves techniques include: reflection measurements with the use of an open-ended coaxial probe (Skierucha et al., 2004; Agilent, 2006), transmission measure‐ ments with the use of materials' samples placed inside transmission lines and microwave resonators (King, 2000).

The complex relative permittivity *ε \** of a material can be expressed in the following complex form:

$$
\varepsilon^\* = \varepsilon^\circ \text{ - } j\varepsilon^\circ = \varepsilon^\circ \text{ - } j\left(\varepsilon\_d^\circ + \frac{\sigma}{\varepsilon\_0 \omega}\right) \tag{8}
$$

The real part *ε '* is referred to as the dielectric constantand represents stored energy when the material is exposed to anelectric field, while the loss factor *ε ''* , which is the imaginary part, influences energy absorption and attenuation, *ε<sup>d</sup>* '' stands for the contribution due to di‐ poles rotation,*<sup>σ</sup>* (S <sup>m</sup>-1) is the ionic conductivity, *<sup>ω</sup>* (rad <sup>s</sup>-1) is the angular frequency and *ε*0 is the permittivity of free space or vacuum (8.854 10-12 F m-1), and *j* = -1. Mechanisms that con‐ tribute to the dielectric loss in heterogeneous mixtures include polar, electronic, atomic and Maxwell–Wagner responses. Aquametry measurements at RF and microwave frequencies are of practical importance and they are currently used for applications in food processing (Venkatesh and Raghavan, 2004), food treatment (Marra et al., 2009) and quality determina‐ tion of biomaterials and food products (Wang, 2003; Sosa-Morales et al., 2010).

#### *<IP_ADDRESS>. TDR technique*

Time domain reflectometry (TDR) is a fast, accurate, and safe technique. The basic principle of time domain reflectometry (TDR) is the same as in radars. The system sends an electro‐ magnetic pulse along the waveguide, which reflects on the mismatch impedance. This tech‐ nique assumes that the material is homogeneous in the vicinity of the waveguide forming a TDR sensor.

*<sup>v</sup>* <sup>≈</sup> *<sup>c</sup>*

*ECb* <sup>≈</sup> *<sup>ε</sup>*(*θv*)

the length of TDR probe rods inserted into the soil.

apparent) electrical conductivity, *ECb* (S <sup>m</sup>-1

free water, solid phase and air.

*2.3.3. Material specific calibration*

nisms in the process being examined.

ton, 1985)

*<sup>ε</sup>*(*θv*) <sup>=</sup> *<sup>c</sup>*

*<sup>n</sup>* <sup>=</sup> <sup>2</sup>*<sup>L</sup>*

where *c* is a velocity of light in free space, *ε*(*θv*) is the real part of the complex dielectric per‐ mittivity dependent on its volumetric water content, *n* is the medium refractive index; *L* is

Also, the amplitude of the pulse at the point (b) decreases with the increase of soil bulk (or

<sup>120</sup>*π<sup>L</sup>* ln( *Uin*

where *Uin* and *Uout* are the amplitude of the pulse before and after attenuation caused by the pulse travel twice a distance of the probe length, *L*. The value of *ECb* is a strong indicator of the ionic concentration in soils, i.e. its salinity (Malicki and Walczak, 1999; Friedman, 2005). The TDR determined dielectric constant can be utilized to determine the volumetric water content, *θv*, on the base of empirical calibration (Topp et al., 1980; Malicki and Skieru‐ cha, 1989; Malicki et al., 1996) or theoretical models (Roth et al., 1990; Or and Wraith, 1999) of the sensor in the multiphase medium that includes the fraction of bound water beside