**Author details**

Carlos Alberto Burguillos Fajardo

1 Regional Centre for Space Science and Technology Education in Asia and the Pacific, International School Beihang University, Beijing, China

2 Bolivarian Agency for Space Activities (ABAE), Simón Rodríguez Technology Complex, Caracas, Venezuela

\*Address all correspondence to<EMAIL_ADDRESS>cburguillos@abae. gob.ve

© 2019 The Author(s). Licensee IntechOpen. This chapter is 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.


**1. Introduction**

Communications have acquired an important role in the development of concepts such as the internet of things (IoT) [1]. The IoT provides emerging and novel applications to transform cities in smart cities by improving the quality and performance of its public services [2,3]. Smart cities are capable of sensing, integrating, and analyzing critical information in city operation and evolution to ensure sustainability and quality of life through the advancement of urban electronic communications in interoperable systems [4–6]. One of the principal goals in smart cities is to count on smart mobility. Smart mobility consists of transport that defines an innovative infrastructure for traffic and transport that saves resources by using new technologies for maximum accessibility and efficiency for citizens [7]. In the IoT field, there exist specific networks that can improve and grow smart mobility; these are known as vehicular networks (VN) [8]. These networks carry out vehicle to vehicle (V2V), vehicle to infrastructure (V2I) [9], and vehicle to everything (V2X) communication [8]. The development and implementation of VN contribute to the integration of mobility with everything. That is, being reached by the concept of smart [1,10], which ranges from smart devices and homes to smart cities. Currently, several communications systems integrate with vehicles due to the growing demand for connectivity in vehicular environments [11,12]. Such integration is regulated under the framework of the IEEE 802.11p

standard [11,13]. At present, several works on VN have employed communications systems based on IEEE 802.11p—this standard is the core for the wireless access for vehicular environments [14–17]. The IEEE 802.11p standard allows vehicular communications defined in the physical (PHY) and medium access control (MAC) layers in the dedicated short-range communications (DSRC) protocol stack [18]. In DSRC, the 5.85–5.925 GHz range is divided into seven channels of 10-MHZ bandwidth each, which is the half bandwidth of 802.11a [18]. This standard offers short transmission distance less than 300 m and data rates ranging from 6 to 27 Mb/s [14]. Besides, 802.11p uses a carrier frequency of 5.9 GHz [16]. Moreover, recent developments have been carried out proposing a system that combines the traditional 802.11p standard VANET networks with LTE networks to form a hybrid Cloud-VANET to provide an efficient routing protocol with low latency and high reliability along with less congestion [19]. Reference [20] presents an analysis of the obtained results of a V2V framework developed on VANETs to reduce large amounts of traffic from LTE networks.

A relevant element in the design of vehicular communication systems is the antenna, which must satisfy the appropriate radiation specifications [21]. Besides, the antennas must ensure that there is no intervention with the vehicle operation. Usually, antennas are made of metal on dielectric substrates, which can be unattractive for the growing need to optimize spaces and offer better technical and aesthetic performance. Some examples of this are in references [22,23]—present antennas for 802.11p standard, but are implemented in an opaque substrate. Even in reference [22], the proposed design is a volumetric structure. Furthermore, in [24], a fractal antenna design is presented—this antenna was fabricated using Polyvinyl chloride as a transparent substrate, but it uses copper for the radiation element, making it not completely transparent. Therefore, demand is emerging for research, development, and use of transparent antennas that can be integrated into windshields and windows, solar cell panels, mobile devices, and in the automotive industry, [25,26]. Finally, it has to be mentioned that there exist other transparent antenna designs for vehicular communications, but they operate within the UHF and VHF bands [27,28].

Additionally, transparent antennas start to be an option in the application of RF energy harvesting. Some examples of these applications are described by [29,30]. For the development of transparent antennas, various materials and configurations have been tested to improve efficiency. Some of the transparent conductive films that have been tested for use in this type of antennas include silver-coated polyester film (AgHT-8) [31], indium-tin-oxide (ITO) [32], Indium-zinc-tin oxide (IZTO) [33], Silver grid layer coating (AgGL) [34], and zinc oxide heavily doped with gallium (GZO) [25]. Besides, some transparent antennas designs employ mesh metal films printed on glass substrates—these metal layers present a low sheet resistance [35,36]. Recently, mesh metal films are applied in transparent antennas at 60 GHz to improve their performance [37].

On the other hand, there are many investigations of transparent antenna geometries. In reference [26] a transparent antenna for WLAN application in 5 GHz is introduced, whose topology is inspired in a flower with six petals built into indium-tin oxide film (ITO) as a transparent radiation element. Several antennas designs use coplanar wave feed [31,38,39], because the transparent conductive film is on just one side of the substrate. In [31], a coplanar waveguide-fed transparent antenna for extended ultrawideband applications is presented, using AgHT-8 thin film as conductive material with a staircase-shaped rectangular radiator and a modified partial ground. Moreover, references [38,39] report a multiband transparent antenna using a coplanar waveguide for 5G applications.

Notwithstanding the vast developed area, a remaining problem for designing transparent antennas based on conductive films with sheet resistance over 5 Ohms, (mainly with ITO) [26,29,30], is to obtain a multiband behavior with narrow bandwidths. Typically, the transparent antennas with ITO show a fractional bandwidth higher than 20% generating a UWB response. In this work, a multiband operation achieves, and the frequencies bands are well defined.

In this work, the design of a fully transparent antenna using ITO-coated glass with a coplanar waveguide (CPW)-fed slot dipole with a multiband operation, IEEE 8002.11p (5.9 GHz), and LTE sub 6 GHz bands, is proposed for future vehicular communications applications. In order to obtain the desired frequencies, a modified ground plane was introduced with symmetrical rectangular stubs [40,41]. The antenna characterization is performed by considering the measured reflection coefficient and the radiation pattern. Even though the ITO has a high sheet resistance, the experimental results obtained satisfy the frequency requirements for the standard IEEE 802.11 and LTE sub 6 GHz bands. Besides, the experimental results are similar in behavior to the simulated ones, but with a slight shift in frequency. Nevertheless, this good concordance is unusual in other reported transparent antennas based on conductive films with a high sheet impedance. The main contributions of the proposed design are a fully transparent antenna that operates at frequencies for vehicular communications standards, and small size.

#### **2. Materials and Methods**

In this research, Adafruit commercial indium-tin-oxide (ITO)-coated glass with a thickness of 1850 Å was employed to fabricate the proposed antenna. The transparent conductive oxide (TCO) sheet resistance (Rs) was estimated by the well-known method of the four-point probe [42] performed over thirteen positions on a film sample, as can be seen in Figure 1. Table 1 presents those results and the final average for Rs of 7.943 ohm/square that was used for the design and simulations of the antenna. The substrate is glass with relative permittivity and thickness of 5.5 and 1.1 mm, respectively. In the development of antennas, those factors are significant to determine the frequency responses and antenna efficiency [32]. Therefore, it is important to incorporate them into the antenna design and simulation process. Moreover, a coplanar waveguide-fed slot antenna with impedance matching stub was chosen to obtain a multiband response through a crossmatch technique for a proper impedance matching [40,41], and allowing both the radiator and the ground plane to be on the same side for fabrication ease. High-frequency structural simulator (HFSS, ANSYS, PA, US) was used to design and optimize the chosen topology for the transparent antenna through parametric analysis.

**Figure 1.** Schematic positions on indium-tin oxide (ITO) film placed on a glass slide for sheet resistance (Rs)/square measurement.

**Table 1.** Rs/Square Measurements Obtained on ITO Film.

Through a parametric analysis in the HFSS simulator, the optimized antenna dimensions were obtained, and they are shown in Figure 2 and described in Table 2, respectively. The antenna feedline was calculated to obtain a coplanar waveguide (CPW) with a characteristic impedance of 50 ohms. The proposed transparent antenna is a capacitively coupled CPW-fed slot, dipole antenna with two pairs of protruded slot lines with different lengths, W1 and W2. The resonant frequencies correspond to the two different resonant paths. The two resonance frequencies for the design are 1.9 GHz and 5.9 GHz, which are used in LTE and 802.11p, respectively. Besides, in the parametric analysis, we made variations over the parameters W1, W2, and Wp1, to reach the desired frequency bands performing the matching impedance and observe their impact on the antenna design.

**Figure 2.** Antenna configuration with dimensions.

**Table 2.** Dimensions of the Proposed Antenna.

In [40], it is mentioned that the resonant frequencies are independently controlled by a common aperture and the three pairs of respective thin slots. However, in our design, the variation of the length W1 shift both frequencies, as shown in Figure 3a. Moreover, Figure 3b shows variations in the higher frequency due to change in the length W2, while the lower frequency is fixed. Similar behavior is observed in Figure 3c when varying the width of the central patch, the high frequency is mainly affected, whereas the lower band is minimally changed. The reason is attributable to the fact that lengths of W2 and Wp1 are closer to the shortest wavelength [41]. It is important to mention that in our simulations, the SMA connector was considered.

**Figure 3.** Simulated reflection coefficient of the ITO antenna for three parameters variations: (**a**) W1; (**b**) W2; (**c**) Wp1.

#### **3. Results and Discussion**

After obtaining the results through numerical simulation, the antenna was manufactured, and measurements of return loss, gain, and radiation diagrams were performed. The transparent antenna was fabricated by using a photolithography process. The transfer of the antenna geometry to the ITO-coated glass was made using a photosensitive film, which was exposed to UV light through a mask with the antenna geometry. Then the area exposed was removed to continue with the etching of the ITO films with a (1:1) solution of hydrochloric acid (HCL). This last process was done at 40 ◦C temperature for 2 min. Finally, we remove the photoresistant layer. Besides, an SMA connector was employed to connect the antenna; this connector was soldered to the transparent antenna using indium (In) solder spheres. The fabricated antenna placed onto the BUAP label is shown in Figure 4, where the transmittance of the ITO can be observed. The vector network analyzer (VectorStar, Anritsu) was used to measure the S11 from 0.5 GHz to 12 GHz. The simulated and measured return loss (S11) are shown and compared in Figure 5. The measured S11 at 5.9 GHz is −16.7 dB, which shows a good agreement with the simulated results.

**Figure 4.** Manufactured antenna photography.

**Figure 5.** Comparison of simulated and measured return loss parameters.

Although a slightly detuned response is obtained from the measurement, related to fabrication flaws, each fractional bandwidth (FWB) remains, as can be seen in Table 3, showing the FBW for every band in simulation and measurement. The measured FBWs for S11 below −10 dB at the lower band is 31.34% (1.82 to 2.5 GHz), and at the upper band is 87.03% (4.66 to 11.84 GHz), which is large enough to cover the 5.9 GHz required frequency. Thus, experimental results fulfill the communication IEEE 802.11p standard for the required band.

**Table 3.** Simulated (S) and Measured (M) Fractional Bandwidth Comparison. FBW: Fractional Bandwidth.

Figure 6 shows the simulated and measured 2-D radiation patterns of the proposed antenna at 2.1 and 5.9 GHz. At both frequencies, the H-plane radiation pattern presents omnidirectional behavior, whereas the E-plane radiation pattern is bidirectional. Moreover, to complete the characterization of the antenna, the peak gain of the antenna was simulated and measured at 2.1 and 5.9 GHz—Table 4

summarizes the obtained peak gains. The measured radiation patterns and peak gains are in concordance with the simulate results. Besides, the antenna efficiency at 2.1 and 5.9 GHz was simulated; the obtained values are 10% and 15%, respectively. These gain peaks and efficiency values are in agreement with those reported for other antennas that use ITO as a conductive film [43].

**Figure 6.** Simulated and measured radiation patterns: (**a**) H-plane patterns at 5.9 GHz; (**b**) E-plane patterns at 5.9 GHz; (**c**) H-plane patterns at 2.1 GHz; (**d**) E-plane patterns at 2.1 GHz.

**Table 4.** Simulated (S) and Measured (M) Peak Gain.

Furthermore, the current distribution for the transparent antenna was obtained by simulation at 2.1 and 5.9 GHz, and it is presented in Figure 7. From Figure 7a, it is observed that the distribution current at 2.1 GHz is more intense on the feedline and, at the bottom of the middle path. Another significant amount of current is around the geometry of the antenna. On the other hand, at 5.9 GHz, the current distribution is mainly on the feedline, and at the middle patch. However, there is a significant amount of current between the resonators and at the largest resonator edges, as shown in Figure 7b.

**Figure 7.** Simulated distribution current at (**a**) 2.1 GHz and (**b**) 5.9 GHz.

Finally, Table 5 presents a comparison of the proposed antenna with other transparent antennas. From the table, it can be noted that the antennas manufactured with ITO [22–24] do not report a fair agreement between the simulated and measured values of the reflection coefficient throughout the entire frequency range of the study, whereas in this work we can see a reasonable concordance between simulated and measured values. The frequency shift may be due to the manufacturing process and the variations in the permittivity of the substrate.

**Table 5.** Comparative Analysis with Other Transparent Antennas.

\* (M) Measured, (S) Simulated.

## **4. Conclusions**

A CPW-fed fully transparent antenna for vehicular communication standards was designed, manufactured, and measured. The crossmatch technique was used for the impedance matching to achieve the target frequencies through parametric simulation. The antenna was designed and fabricated using commercial ITO-coated glass with a sheet resistance of 8 ohms/square. Opposite to other works that also use conductive films with a high sheet resistance, the experimental parameters obtained showed a behavior following the one simulated. Despite the frequency shift in the measured reflection coefficient, the fabricated antenna covers the range of 1.82–2.5 GHz at the lower band and 4.66–11.84 GHz at the upper band for 2.1 GHz and 5.9 GHz requirements, respectively. Those ranges comply with the IEEE 802.11p standard and LTE sub 6 GHz communication bands for vehicular communications applications. The proposed antenna achieves an omnidirectional radiation H-plane patterns. As expected, the peaks gain of the antenna, in the desired frequencies, were negative. Additionally, the proposed antenna presents low radiation efficiency under 15%. These behaviors are due to the sheet resistance of the ITO film, and it can be improved by increasing the thickness of the ITO film, but it would reduce the transparency of the antenna.

**Author Contributions:** Conceptualization, J.I.T.-F., R.T.-M., J.M.M.-P., M.A.V.-A., E.I.T.-F., M.L.-L., and E.C.-B.; methodology, J.I.T.-F., R.T.-M., and E.C.-B.; software, J.I.T.-F., R.T.-M., M.L.-L., and E.C.-B.; validation, J.I.T.-F., R.T.-M., and E.C.-B.; formal analysis, J.I.T.-F., R.T.-M., J.M.M.-P., E.I.T.-F., M.L.-L., and E.C.-B.; investigation, J.I.T.-F., R.T.-M., and E.C.-B.; measurements, J.I.T.-F., R.T.-M., and E.C.-B.; data curation, J.I.T.-F., R.T.-M., and E.C.-B.; writing—original draft preparation, J.I.T.-F., R.T.-M., and E.C.-B.; writing—review and editing, J.I.T.-F., R.T.-M., J.M.M.-P., E.I.T.-F., M.L.-L., and E.C.-B.; supervision, R.T.-M. and J.M.M.-P.; project administration, J.I.T.-F., and R.T.-M.; All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** With thanks to the laboratory of characterization of systems based on microwaves at FCE-BUAP where all experimental characterizations were carried out. J.

**Conflicts of Interest:** The authors declare no conflict of interest.


**4. Basin formation and migration in central Kinki since the Pliocene**

Three sedimentary basins are arranged E-W latitudinally in the eastern part of "Second Setouchi Inland Depression of [25]: Lake Tokai, Paleo-Lake Biwa and Paleo-lake (bay) Osaka. All are filled with the Plio-Pleistocene deposits (Figure 11). They are respectively named Tokai,

**Figure 10.** Bouguer gravity anomaly map. The Bouguer density is 2670 kg/m3, and contour interval is 2 mGal

Kobiwako, and Osaka Groups. Comparing of the sedimentary basin transition between Paleo-Lake Biwa and Lake Tokai, the geohistory in central Kinki Region is known subdivisible by tectonosedimentary facies of about 3.0 Ma and 1.2-1.5 Ma (Figures 12, 13) which suggests that the change of tectonic stress state of this province took place simultaneously throughout these sedimentary basins. To complete the geohistory of Paleo-lake Biwa, patterns of sedimentary basin transition must be discussed. According to Yokoyama ([26], [27]), the geohistory of Paleo-Lake Biwa has four stages: Older I, Older II, Actual I, and Actual II. First, Paleo-Lake Biwa appeared in the Iga Basin and clay-dominant sediments were deposited in the water body ("Iga-ko") (a and b in Figure 12) [28]. In the second, the sedimentary basin center shifted its place to the north from Iga Basin to Ohmi Basin, forming a stable water body ("Sayama-ko") with massive clay deposition (c and d in Figure 12). Northward shifting of the sedimentary basin was inherited (Older II Stage) (e and f in Figure 13). During the time from Older II stage to Actual I stage, the center of the sedimentary basin migrated northwestward on a large-scale. Great amounts of gravel are represented as final sediments of Older II stage (g in Figure 13). The sedimentary basin of Actual I stage shifted its place gradually to west, accompanied by upheaval of the eastern mountain area. This explanation is supported by results of lithology, paleocurrent and sedimentological studies of the deposits of the Kosei area and data from 1,000

**4. Basin formation and migration in central Kinki since the Pliocene**

218 Mechanism of Sedimentary Basin Formation - Multidisciplinary Approach on Active Plate Margins

Three sedimentary basins are arranged E-W latitudinally in the eastern part of "Second Setouchi Inland Depression of [25]: Lake Tokai, Paleo-Lake Biwa and Paleo-lake (bay) Osaka. All are filled with the Plio-Pleistocene deposits (Figure 11). They are respectively named Tokai,

**Figure 9.** Active structure revealed by horizon A (Boundary of T and S bed) since about 0.43 Ma) of the seismic reflec‐ tion survey [19] Meshed part: depth of A horizon more than 400 m, Dotted part: depth of A horizon lower than 300 m

**Figure 11.** Basement and Pliocene-Quaternary sediment distribution in and around Lake Biwa and Ise Bay region. "Kinki Triangle" region is shown in inset figure. Paleogeographical regions such as "Chubu Tilting Block", Lake Tokai, Paleo-lake Biwa, and Paleo-lake (bay) Osaka are shown. MTL: Median Tectonic Line, ATL: Arima-Takatsuki Tectonic Line, I: Ikoma Fault, H: Hanaore Fault, B: Biwako-seigan Fault zone, Ya: Yanagase Fault, Ic: Ichishi Fault, Yo: Yoro Fault

m drilling cores at the rivermouth of the Yasu River [29]; [30]; [31]. The gravel of the uppermost part of the Kobiwako Group in Kosei Area (western side of present Lake Biwa) constitutes sediments of the last Actual I stage. These gravels were the first sediments from present western Hira Mountains. Subsequently, the crustal movements along the Katata Fault (southern part of Biwako-seigan Fault zone) became more active. Thereafter, in actual II stage, the area of actual northern lake ("Hokko") basin of present Lake Biwa began to subside rapidly.

**5. Tectonic basin formation in and around Lake Biwa: Chronological**

As described previously, the geohistory in central Kinki region had two conspicuous episodes of ca 3.0 Ma and of ca 1.2-1.5 Ma. A similar pattern of basin transition was revealed as recognized in both sedimentary basins of Lake Tokai and Paleo-lake Biwa (Figure 14), which suggests that the changes of the tectonic stress state were common throughout that province. The sedimentary basins before ca 3.0 Ma (Stage 1 of Lake Tokai and older I stage of Paleo-lake Biwa) are characterized mainly by E-W arrangement of depressional zone and their northward migration. Those characteristics might be attributable to the upheaval of the southern area under the tectonic stress state in N-S direction. However, in the middle of Stage 1, Lake Tokai received a large amount of gravel supply from the east, which was related to the movements of "Chubu Tilting Block". Kuwahara[33] discussed tectonism of eastern area of Ise Bay (the area from Nohbi Plain to mountains). He stated that this area had received tilting movement since Pliocene and this movement formed the topographic contrast between the sedimentary

**Figure 12.** Paleogeographic map of the central Kinki Region including Paleo-Lake Biwa and Lake Tokai area from the early Pliocene to 1.2 – 1.5 Ma [32] a: Initial Stage I of Lake Tokai and Initial Older Stage of Paleo-Lake Biwa, b: Stage I of Lake Tokai and Older Stage of Paleo-Lake Biwa, c: d: Older stage II of Paleo-Lake Biwa and Stage II of Lake Tokai

Tectonic Basin Formation in and Around Lake Biwa, Central Japan

http://dx.doi.org/10.5772/56667

221

**development and mechanism**

The process of basin transition in and around Paleo-Lake Biwa is summarized as follows:

Tectonic Basin Formation in and Around Lake Biwa, Central Japan http://dx.doi.org/10.5772/56667 221

**Figure 12.** Paleogeographic map of the central Kinki Region including Paleo-Lake Biwa and Lake Tokai area from the early Pliocene to 1.2 – 1.5 Ma [32] a: Initial Stage I of Lake Tokai and Initial Older Stage of Paleo-Lake Biwa, b: Stage I of Lake Tokai and Older Stage of Paleo-Lake Biwa, c: d: Older stage II of Paleo-Lake Biwa and Stage II of Lake Tokai


*3.3. Enzymatic Hydrolysis*

The results included in this section provide a quantitative assessment of the susceptibility of selected delignified and autohydrolyzed-delignified solids towards enzymatic hydrolysis. The composition of the solids is listed in Table 5. The experimental plan included acid-catalyzed organosolv treatments (assays 18–19), and experiments in ethanol/NaOH media (runs 13–14).

**Table 5.** Substrates and composition of solids employed as substrates for enzymatic hydrolysis. Data expressed as average values ± standard deviations.

Both AS and the solids obtained under the conditions listed in Table 5 presented different behavior as hydrolysis substrates. Figure 1a shows the cellulose conversions into glucose achieved at selected reaction times. The highest cellulose conversion (74.2%, corresponding to a volumetric glucose concentration of 28.52 g/L) was reached when the solids from exp. 18 (HS subjected to acid organosolv delignification) were hydrolyzed for 96 h. In comparison, the solid from exp. 19 (AS delignified under the same conditions) was poorly hydrolyzed (conversion below 15%, or 5.62 g glucose/L). HS delignified with aqueous NaOH/ethanol under the conditions of exp. 13 showed higher hydrolysis conversion (52.5%) than the one achieved using AS delignified under the same conditions (exp. 14). Despite the low conversions reached in the experiments performed with autohydrolyzed or autohydrolyzed-delignified solids (obtained in exp. 14 and 19), the highest enzymatic susceptibility was observed for the substrate from exp. 14, carried out in aqueous NaOH/ethanol media. In comparative terms, the susceptibility of the diverse substrates to hydrolysis varied as follows: AS < acid-catalyzed-organosolv AS (exp. 19) < aqueous NaOH-organosolv AS (exp. 14) < aqueous NaOH-organosolv HS (exp. 13) < acid-catalysed organosolv HS (exp. 18).

Literature data reports that the lignin content affects the enzymatic hydrolysis, since cellulases may bound to lignin irreversibly [40]. In our study, the solid from exp. 18 (which showed the highest conversion into glucose) presented the highest cellulose/lignin ratio (1.86). In comparison, the solid from exp. 19 (cellulose/lignin ratio, 1.36) reached considerably lower conversion into glucose than the solids from exp. 13 and 14 (which presented cellulose/lignin ratios of 0.68 and 0.87, respectively). Çöpür et al. [27] reported the behavior of different pretreatment techniques on regard to their efficiencies for the subsequent enzymatic hydrolysis of glucan into glucose from hazelnut husks. The highest glucan to lignin ratio of pretreated solids was used as criteria for the subsequent saccharification. Then, they reported a glucan to lignin ratio of 0.99 when HS were treated with combined steam explosion-NaOH delignification, and a high conversion of glucan into glucose (74.7%) in enzymatic hydrolysis performed at LSR 20. Ho¸sgün and Bozan [20] compared the enzymatic susceptibility of HS treated by different methods (acid, alkali, and steam) and found that the maximum glucose recovery (58.7%) corresponded to samples pretreated with NaOH. Similar results were reported with alkali delignified HS when solids were enzymatically hydrolyzed at higher LSR and ESR than were used in this work [28].

Hallac et al. [43] reported that the relationship between the lignin content of pretreated *Buddleja davidii* samples and their enzymatic susceptibility was not proportional. Huijgen et al. [41] compared the digestibility of delignified and prehydrolyzed-delignified wheat straw, and concluded that prehydrolysis prior to organosolv improved the enzymatic cellulose digestibility, despite the low lignin removal in delignification. Yang and Pan [44] discussed some aspects of the complexity of lignin effects on the enzymatic hydrolysis: a) high lignin content does not necessarily predict poor enzymatic digestibility; b) not all lignins have the same inhibitory effect on enzymatic hydrolysis of cellulose, since lignin from different sources had varying inhibitory effects, greatly related to lignin structures and properties; c) not all the lignin in the same substrate has the same inhibitory effect. On the basis of these observations, they studied the inhibitory effect of lignin with varied physicochemical properties from different biomass sources on the enzymatic hydrolysis of cellulose, and concluded that the lignin inhibition to enzymatic hydrolysis of cellulose was related to the hydrophobicity or the phenolic hydroxyl groups of lignin.

The data in Figure 1b show that the residual xylan in the hydrolysis substrates was extensively hydrolyzed into xylose. For example, in exp. 18, 80% of xylan was converted into xylose, which reached 7.03 g/L. Sun et al. [30] reported that some accessory enzymes in the enzymatic hydrolysis of natural lignocellulosic substrates favored an efficient conversion, and underlined the role of the high specific xylanase activity of the complex Cellic CTec2.

**Figure 1.** Effect of the enzymatic hydrolysis in the conversion of: (**a**) cellulose to glucose; (**b**) xylan to xylose, of spent solids from HS and AS processed under selected conditions of alkaline-organosolv, acid-catalyzed organosolv, and AS.

### **4. Conclusions**

This study deals with the integral fractionation of HS, based on selected delignification methods (in alkaline, alkaline-organosolv, organosolv or acid-catalyzed organosolv media). Both HS and autohydrolyzed HS (AS) were used as substrates for delignification.

HS treated in acid-catalyzed organosolv media reached the highest delignification degree (65.3%), enabling the production of valuable hemicellulose-derived products (about half of them in the form of oligosaccharides), with limited cellulose losses from the solid phase. Alternatively, autohydrolysis led to the partial solubilization of hemicelluloses (mainly as oligosaccharides), and the subsequent acid-catalyzed organosolv of AS resulted in the simultaneous solubilization of the remaining hemicelluloses (87.7%) and lignin (47.9%).

The enzymatic hydrolysis of solids from delignification or autohydrolysis-delignification treatments confirmed that acid-catalyzed organosolv of HS provided the best substrate for enzymatic hydrolysis (74.2% cellulose conversion into glucose, with a volumetric concentration of 28.52 g glucose/L).

Then, the strategy approaches reported in this work can be considered as "conventional" but promising alternatives for the integral fractionation of HS in the scope of biorefinery.

**Author Contributions:** S.R. designed the research and discussed the data. S.R., L.L., A.M. and C.V. performed experiments and analyzed the data. S.R. and J.C.P. prepared the original draft. All authors discussed the data. All authors have read and agreed to the published version of the manuscript.

**Funding:** S.R. contract was supported by Ministerio de Ciencia, Innovación y Universidades (IJC2018-037665-I).

**Acknowledgments:** S.R. thanks Ministerio de Ciencia, Innovación y Universidades for her "Juan de la Cierva" contract (IJC2018-037665-I).

**Conflicts of Interest:** The authors declare no conflict of interest.


*3.1.3 Sustainable yield index (SYI) and green water use efficiency (WUE)*

SYI indicates the stability of crop yields in the long run. The high index shows the low variation of yield increase over years. Application of mineral fertilizers N + P + K + Mg increased SYI and WUE of crop. Omitting nutrient and application

**Figure 4.** *Effect of balanced nutrition, omitting nutrient, and FYM on the trend of average yield.*

*Effect of Balanced and Integrated Crop Nutrition on Sustainable Crop Production in a Classical… DOI: http://dx.doi.org/10.5772/intechopen.102682*

of only FYM decreased SYI and WUE compared to the balanced nutrition. The WUE was reduced by 63%, 34%, and 7–59%, respectively at without any fertilizer, application of only FYM, and omitting nutrients compared to the N + P + K + Mg treatment (**Figure 6**). The reduction of WUE is directly related to the decline in crop yield because of nutrient omission and application of only FYM.

#### *3.1.4 Nutrient use efficiency*

Nitrogen use efficiency (NUE) at the balanced nutrition (N + P + K + Mg) treatment was 77%. Any lack of nutrients reduced the NUE to 49% - 73% (**Figure 7**). P use efficiency (PUE) at the balanced nutrition was 49%. Omitting Mg, K + Mg, and N + Mg resulted, respectively 46%, 42%, and 25% PUE compared to the N + P + K + Mg treatment (**Figure 7**). The balanced nutrition resulted in the highest K use efficiency (KUE) of 84% compared to omitting nutrients and application of only FYM. The KUE at omitting Mg, P + Mg, and N + Mg fertilizers and only FYM

**Figure 6.**

*Effect of balanced nutrition, omitting nutrient, and FYM on average WUE and SYI of the crop (n = 62 years).*

application were, respectively 78%, 77%, 37%, and 75% (**Figure 7**). The highest nutrient use efficiencies were achieved in the treatment with the balanced supply of nutrients for crop demand. Application of FYM without mineral fertilizer decreased N and K use efficiencies, because of the lower plant availability of N and K in the FYM. P and K fertilizers application without N resulted in a very low PUE and KUE, because of the very low yield and poor recoveries of P and K.

## *3.1.5 Soil P2O5 and K2O contents*

P and K fertilizers application affects soil P2O5 and K2O content. The balanced nutrition (N + P + K + Mg) increased soil P2O5 and maintained the soil K2O in comparison to the omission of P and K respectively.

The P2O5 content of loamy sand soil on arable land is classified as 'very low' (below 3), 'low' (4–9), 'medium' (10–18), 'high' (19–32), and 'very high' (above 33) mg P2O5 per 100 g soil at 0–30 cm depth [25]. At the start of the trial the soil P content, as well as the K level were therefore classified as medium. P fertilizer application increased soil P2O5 content toward very high during 1958–1983: the inadequate N rate during 1958–1980 (**Table 2**) and the limited potato growth in 1973–1982 caused a low crop yield (**Figure 4**) that resulted in an accumulation of P fertilizer in the soil. Increased crop yield after 1982 due to increased N fertilizer rate and cultivating potato variety resistance to nematodes reduced soil P2O5 content during 1984–1996. P fertilizer application generally increased soil P2O5 content to 'high' level, but omitting P fertilizer reduced the soil P2O5 content compared to the initial measurement in 1958 (**Figure 3**).

The K2O content of loamy sand soil on arable land is classified as 'very low' (below 3), 'low' (4–9), 'medium' (10–18), 'high' (19–32), and 'very high' (above 33) mg K2O per 100 g soil at 0–30 cm depth [25]. Application of K fertilizer-maintained soil K2O content at the 'medium' range, while the omission of K fertilizer decreased soil K2O content to the 'low' level (**Figure 2**). Application of K fertilizer increased the soil K2O content during the early decades, because of low K removal from the soil. The decreasing soil K2O content after 1981 was generally driven by combined effects of increased K removal from the soil with high crop yield and loss of K by leaching on sandy soil.

A low crop yield (**Figure 1**) produced a low PUE and KUE (**Figure 7**), at P + K mineral fertilizers application without N, resulted in the highest soil P2O5 and K2O contents (**Figures 2** and **3**). Soil P2O5 and K2O analysis at 30–90 cm in 1987, 2008, and 2018 showed residual P and K fertilizers movement below 30 cm depth. P + K mineral fertilizers application without N increased the soil P2O5 and K2O contents respectively by 43% and 49% in 30–60 cm and by 48% and 96% in 60–90 cm depth compared to the application of N + P + K mineral fertilizers (data not shown).

#### *3.1.6 Soil organic matter and soil pH*

Improvement of soil organic matter positively influences soil fertility through its impact on the chemical, physical, and biological properties of a soil. The soil organic matter was measured as soil C (carbon) content. The soil organic C decreased in comparison to the initial value of 2.1% measured in 1958, because crop residues were removed from the field during 1958–2009. It was slightly increased with mineral fertilizer and FYM application compared to the treatment without any fertilizer (**Figure 8**). During 1959–1973, the soil organic C was not measured.

*Effect of Balanced and Integrated Crop Nutrition on Sustainable Crop Production in a Classical… DOI: http://dx.doi.org/10.5772/intechopen.102682*

The soil pH was optimized by lime application to avoid the negative effect of pH on nutrient availability. Lime (CaO) applied every 3 years to the whole field at 1000 kgha−1 increased soil pH compared to the initial pH measured in 1958 (**Figure 9**).


**4. Soil Loss Characterization**

Characterization of soil loss is very important for environment and natural resources. In erosion control planning, soil loss estimates for a particular site are determined using a prediction model and compared with a T-value for that site [31]. The Universal Soil Loss Equation (USLE) is an example of a model used extensively to predict erosion from crop‐ lands and rangelands. More recently, the Agricultural Research Service, Forest Service, and the Bureau of Land Management have joined in a cooperative effort, the Water Erosion Prediction Project (WEPP). WEPP has been implemented to develop an improved model based on modern technology for estimating soil erosion by water. WEPP technology is based on fundamental hydrologic and soil erosion processes and is designed to replace the wide‐ ly used USLE [8].

Until recently, prediction of soil loss rates on National Forest lands involved using the USLE [8, 22]. Soil losses were evaluated in the context of potential soil losses, natural soil losses, current soil losses and tolerable soil losses. Potential losses were those that would occur af‐ ter complete removal of the vegetation and litter. Natural losses were associated with the potential natural vegetation community. Current losses were those occurring with current management. Tolerable loss was assumed to be the rate that can occur while sustaining in‐ herent site productivity [8].

The Universal Soil Loss Equation (USLE) is a widely used method for calculating annual soil losses, based on rainfall, runoff, slope, runoff length, soil type and landuse parameters. The equation originally developed on small agricultural plots, but has been adopted for evaluat‐ ing erosion from large watersheds under a wide range of land uses. [41]

$$A = R \times K \times L \times S \times C \times P \tag{1}$$

where *A* represents the soil loss, commonly expressed in tonnes ha-1 year-1. *R* refers to the rainfall erosivity factor, calculated by the summation of the erosion index EI30 over the peri‐ od of evaluation. EI30 is a compound function of the kinetic energy of a storm and its 30 min maximum intensity. The latter factor is defined as the greatest average rainfall intensity experiences in any 30-min period during a storm. *K* is the soil erodibility factor reflecting the susceptibility of a soil type to erosion. It is expressed as the average soil loss per unit of the R factor. *L* is an index of slope length, *S* is a slope gradient index, *C* is an index for the pro‐ tective coverage of canopy and organic material in direct contact with the ground. It is meas‐ ured as the ratio of soil loss from land cropped under specific conditions to the corresponding loss from tilled land under clean-tilled continuous fallow conditions. Finally, the protective factor P represents the soil conservation operations or other measures that control the erosion, such as contour farming, terraces, and strip cropping. It is expressed as the ratio of soil loss with a specific support practice to the corresponding loss with up-anddown slope culture [41].

Soil loss rates have been generally estimated in agricultural areas up to now. Various USLE and GIS combinations have been used to estimate soil loss in forest land [25]. But in this kind of studies, soil loss was determined by quantitatively. For example; in study realiz‐ ed in Taiwan estimating watershed erosion using GIS coupled with the USLE in agricul‐ tural areas. Furthermore a WinGrid system was developed to calculate slope length factor (L) in USLE [4].

Samar [30] developed three soil loss prediction models (WEPP, EPIC, ANSWERS) and used them for simulating soil loss and testing their capability in predicting soil losses for three tillage systems (rigde-till, chise-plow, and no-till). In other study (leave a space after point), USLE and GIS combination were used to predict long-term soil erosion and sediment trans‐ portation from hillslopes to stream networks under different climate conditions and forest management scenarios. Soil erosion was predicted by the USLE watershed level. The GIS utilities are employed to calculate total mass of sediment moving from each cell to nearest stream network [35]. Mısır et al. [25] developed a soil loss model applicable for forest man‐ agement scenarios for forested areas in northern Turkey.

Forest values including soil protection function need to be determined quantitatively in multi-objective forest management planning. Relationships between soil loss and stand structure on a particular must be determined before incorporation of soil protection values into multi-objective forest management plans.