3. Results & Discussion In order to ensure suitability of the developed method for such an application the final method was to meet a number of criteria. Firstly the analysis of the analytes should be carried out in a single method for simultaneous detection in order to improve sample throughput. Furthermore the limits of detection and quantification lie in the ng L-1 range, which corresponds to the concentrations at which such chemical markers occur within surface waters.

Waters OasisTM HLB SPE cartridges and a Waters SunfireTM C18 3.5 µm HPLC column were selected. In the optimised method, two mobile phases were used, where mobile phase A was acetonitrile with 0.1% ammonium acetate and mobile phase B was water with 0.1% ammonium acetate. A gradient flow was used from 10:90 to 60:40 A:B. UV detection was carried out at 206 nm and 200 nm, a 20 µL injection volume was used and the flow rate was set to 0.3 mL min-1.

4. Conclusions This work identifies a means to differentiate sewage and manure nitrate inputs to surface waters, which to date has not been possible. Such research is of interest to various stakeholders, in particular as it allows for more effective application of the ‘polluter pays principle’ and improved management of water bodies in the context of nitrate contamination, since the inputs can be identified. Furthermore, nitrate source determination is considered as an important factor for improving our health and environment, and it has a legislative importance in relation to the Water Framework Directive.

Further investigations that are ongoing involve different analytical techniques for using chemical markers for differentiating sewage and manure. Such research will be carried out with a view of reducing the sample preparation and method development requirements associated with the development and use of an SPE-LC-MS method.

1. Background & Objectives Intensive cropping on light soils has led in many parts of Europe to excessive nitrate leaching.

Various countries have introduced a system of nitrogen (N) application standards. These are fixed values for allowed N input per crop-soil combination, generally independent of expected yield. In the Netherlands, current N application standards for a number of arable and vegetable crops on sandy soils are still too high to meet the target nitrate concentration of 50 mg per litre in groundwater. Reductions of N application standards required to meet this target will cause yield loss. The central question in this study was: to what extent can this yield loss be avoided by differentiating N application standards to local conditions, without compromising environmental performance as expressed in N surplus ?

2. Materials & Methods The hypothesis that differentiation could help resolve the conflict between economy and environment is based on the notion that high-yielding crops are more efficient in N uptake, as well as in utilising the acquired N to make harvestable crop produce. So, attainable yield (Ymax, yield unconstrained by N availability) was taken to be one of the ‘local’ conditions defining N application standards. The second one was N offtake from the soil (U0), that is, N offtake in absence of fertiliser input. This parameter was used as a proxy for soil N supply, values for the latter being unavailable. Here, the hypothesis was that fertiliser N uptake and internal N utilisation by the crop are more efficient if soil N supply is low. Both these two ‘local’ parameters –Ymax and U0 – can be inferred from N response trials. We analysed a total of 223 N response trials of ware potato, starch potato, winter wheat, spring wheat, spring barley, silage maize, onions and sugar beet. First, we tested the hypothesis that Ymax and U0 do affect N uptake efficiency (apparent N recovery, ANR) and internal N use efficiency (1/A, with A for the N concentration in harvested product), and we quantified the relations between these variables by linear regression analysis. Second, we used the resulting regression equations to express actual (N-constrained) yield and N offtake (from soil plus fertilisers) as functions of Ymax, U0 and fertiliser N rate. These functions were then used to address the question raised in the introduction. This was done in the form of a scenario study, where three levels of Ymax were crossed with three levels of U0, thus defining nine sets of local conditions: imaginary fields. Upper and lower values for Ymax and U0 were well within the data range for each crop. The scenario study compared three situations. (A) The reference is N application equivalent to 70% of the current (2011) legal N application standards. All imaginary fields receive the same N rate. Total yield and total N surplus are calculated as the respective sums over all nine fields. (B) N distribution over the nine fields is optimised for maximum total yield, under the boundary condition of equal total N surplus as in (A). In Scenario (C), N distribution over the nine fields is optimised for minimum total N surplus under the boundary condition of equal total yield as in (A). The numerical optimisation in (B) and (C) was executed by Excel Solver.

Nitrogen Workshop 2012

3. Results & Discussion Regression analysis confirmed that N uptake efficiency (ANR) as well as internal N utilisation (1/A) at given N rate increased with higher attainable yield (Ymax) and with lower soil N offtake (U0). The effect of Ymax on A was highly significant (p0.01) in all crops. The same holds for the effect of U0 on A, except in starch potato where the effect was just significant (p0.05). The positive effect of N rate on A was highly significant in all crops, and was linear or quadratic, depending on the crop. In all crops except sugar beet was the effect of Ymax on ANR highly significant. U0 affected ANR in ware potato, starch potato, winter wheat, spring barley, silage maize (all p0.01), and in onion and sugar beet (p0.05). Only in spring wheat there was no such effect. The negative effect of N rate (again linear or quadratic) on ANR was highly significant in all crops, except sugar beet (n.s.). So, all in all, the notion that fertiliser N is more efficiently used when attainable yield is high and soil N supply is low, is considered a valid justification for the differentiation of N application standards to Ymax and U0. We leave aside here the difficulty that Ymax and U0 cannot be known ex ante in the real world. Optimal N distributions were very similar between Scenarios (B) and (C), and both showed widely differing N rates between the nine imaginary fields. In both (B) and (C), N rate differed between fields by as much as 200 (potato, winter wheat), 180 (silage maize), 140 (spring wheat, onion) and 100 (sugar beet) kg per ha-1. In Scenario (B), this differentiation to both parameters (Ymax and U0) indeed helped to reduce yield loss, with strongest effects in maize and potato. While calculated yield loss in Scenario A was 6.42% (maize) and 5.82% (ware potato) relative to yield at the current (2011) N application standards, this loss was reduced to 1.23% (maize) and 3.17% (ware potato). In winter wheat, yield loss was reduced from 3.9% (in A) to 0% (B). In Scenario (C), differentiation reduced N surplus by 10 to 20 kg per ha-1, depending on the crop. We also calculated the benefit of differentiation to Ymax only. This is of practical relevance, because records of actual historical yields can be documented by farmers, to justify increased N application standards, but soil N supply cannot be documented so easily. Simulations of differentiating N application standards to Ymax only, within the same scenarios applied to the nine imaginary fields, revealed that yield loss was reduced by only 1 or 2 %-points.

4. Conclusions In virtually all crops studied here, the efficiencies of N uptake and internal N use are significantly determined by attainable yield and soil N offtake. Due to this pattern, optimal differentiation of N application standards for maximum production within environmental constraints results in widely differing N rates. This differentiation, however, can only contribute substantially to resolving the conflict between economy and environment if it addresses not only attainable yield but also soil N supply.

References The reference list includes only the references to the sources (mostly in Dutch) that document the 223 N response trials. It is too long to include here, but is available upon request.

1. Background & Objectives Agricultural intensification has led to the use of high inputs of nitrogen fertilizers into cultivated land. As a consequence, losses by nitrate leaching or gaseous emissions have increased significantly (Bouwman et al., 2002). Nitrification inhibitors have been shown to decrease N2O emissions in grasslands (Menéndez et al., 2006; Pereira et al., 2010). The objective of this work was to evaluate the effect of 3,4-dimethylpyrazole phosphate (DMPP) on N2O emissions during a whole wheat crop cycle and its possible effect on yield under humid Mediterranean conditions.

2. Materials & Methods This work was conducted in a wheat crop in the Basque Country in 2010-2011 during a whole year, from wheat sowing in December 2010 to sowing of the next crop in November 2011. A randomized complete block factorial design with four replicates was established, with an individual plot size of 40 m2. Three main treatments were applied: a control treatment without fertilizer, a second one with ammonium sulphate nitrate (ASN 26%) and a third one consisting in the combination of ASN with DMPP, available on the market as ENTEC 26. Nitrogen in ASN consisted of 7.5% nitric and 18.5% ammoniacal. Fertilization was split into two amendments: 14th March (tillering), when 60 kg N ha-1 were applied and 12th April (stem elongation), when 120 kg N ha-1 were applied. Grain yields were measured by harvesting an area of 1.5 × 8 m2 per plot. N2O emissions measurements were started on December 2010 after sowing and finished after a whole cropping season one year later.

Measurements were conducted every two weeks, increasing the frequency to three days per week whenever the fertilizer was applied. Cumulative N2O emission during the sampling period was estimated by averaging the rate of emission between two successive determinations, multiplying that average rate by the length of the period between the measurements, and adding that amount to the previous cumulative total. Nitrous oxide emission was measured using closed chambers (Menéndez et al., 2008). Samples were analysed by gas chromatography (GC) (Agilent, 7890A) equipped with an electron capture detector (ECD) for N2O detection. A capillary column (IA KRCIAES 6017: 240ºC, 30 m × 320 m) was used and the samples were injected by means of a headspace autosampler (Teledyne Tekmar HT3) connected to the gas chromatograph. N2O standards were stored and analysed at the same time as the samples.

These losses were 1.47 % of the nitrogen applied. This emission factor agrees with the IPCC (1996) guidelines which assume an N2O emission factor of 1.25 ± 1.0% of fertilizer-N applied, but lower than those described by Ortiz-Monasterio et al. (1996) for irrigated wheat in Mexico (from 1.7 to 3.8 %) in a hot climate. The fact that under our humid Mediterranean conditions wheat does not need to be irrigated can reduce the losses with respect to other climatic zones. The percentage of reduction of N2O losses in the ENTEC treatment with respect to ASN was 10 %. Although this percentage reduction is lower than described by other authors (Linzmeier et al., 2001; Weiske et al.

4. Conclusion In our humid Mediterranean conditions ENTEC efficiently lowers N2O emissions up to the unfertilized levels, maintaining the same crop yield as with ASN fertilizer. Thus, the default emission factor for fertilizers with DMPP should differ from the emission factor for fertilizers without DMPP.

Acknowledgments This project was funded by the Spanish Government (RTA2009-00028-CO3-03 and AGL2009-13339-CO2-01), by the Basque Government (K-EGOKITZEN, ETORTEK 2010-2012), K plus S Iberia S.L.-UPV/EHU (2011.0051) and by the University of the Basque Country (IT526-10).

Materials of this site are available for review, all rights belong to their respective owners.
If you do not agree with the fact that your material is placed on this site, please, email us, we will within 1-2 business days delete him.