Winter legume cover crops or double-cropping in high N-fertilizer maize-based sprinkler-irrigated systems enhance agroecosystem diversity and potentially increase yields. However, the effects on direct N2O emissions and global warming potential (GWP) have not been fully established. For two years, in the Ebro Valley (Spain), four maize-based systems consisted of: long-season maize (Zea mays) with winter fallow period (F-LSM) the reference system; or after a leguminous cover crop (common vetch, Vicia sativa) (CC-LSM); and short-season maize after a cereal crop (barley, Hordeum vulgare) (B-SSM) or after a leguminous crop (pea, Pisum sativum) (P-SSM). They were assessed in terms of productivity, direct greenhouse gasses emissions (GHG: N2O, CH4, CO2), and global warming potential (GWP). Direct GHG emissions were measured using the static chamber technique, while soil parameters were monitored. Crop yields and nitrogen uptake were also quantified. GHG emissions linked to management and inputs were calculated to obtain GWP and greenhouse gas intensity (GHGI). The most productive system (B-SSM) obtained the highest direct (79 %, 35 %, and 30 % higher than the F-LSM, P-SSM, and CC-SSM, respectively) and scaled N2O emissions. The P-SSM system had similar N-uptake-scaled emissions to the monocropping (MC) systems. Irrigation, fertilizer, and farm operations accounted for the 26 %, 31 %, and 27 % of the total indirect emissions, respectively. Fertilizer production-related emissions in B-SSM and F-LSM systems were 172 % and 45 % higher than the average emissions in the systems with legumes (461 kg CO2eq. ha-1). Diversified systems lead to slightly higher GHGI values than the reference system (F-LSM). However, no differences were found between the F-LSM and P-SSM systems in GWP (4521 and 5512 kg CO2-eq. ha-1, respectively) or GHGI (144 and 158 kg CO2-eq. ha-1, respectively). The P-SSM system may be a potential alternative for increasing the diversification of maize-based irrigated agrosystems without increasing GHG emissions.

Aim of the study: Alfalfa is one the most important forage legume crop worldwide but little information is available regarding to greenhouse gas emissions (GHG) under Mediterranean sprinkler-irrigated conditions. Area of study: Middle Ebro valley, Spain Materials and methods: The GHG emissions during two alfalfa growing periods (4th and 5th stands) were evaluated using both the static method chambers and two automatic chambers coupled with a photoacoustic equipment that measured short-term gas emissions. Main results: Year-average CH4 fluxes were -0.71 g C ha-1 day-1, generally no significantly different from zero. Year-average N2O flux was 3.96 g N ha-1 day-1 with higher fluxes associated to some specific large rainfall or irrigation events. Average cumulative emissions of 865 g N ha-1 year-1 were found. We found short-term peaks of N2O (up to 160 g N ha-1 day-1) associated with high values of soil water filled pore space (WFPS) that can go unnoticed using the static chamber procedure. In spite of the higher soil NO3‾ concentration in the alfalfa-precedent field compared to the maize-precedent field, no significant differences in cumulative N2O emissions were observed in the two-month period after alfalfa or maize residues incorporation. Research highlights: Low GHG emissions were found in an irrigated alfalfa crop compared to N-fertilized crops but a deeper knowledge of the limiting factors of denitrification observed during some anoxic events (WFPS>90%) is necessary to properly quantify N2O emissions in irrigated alfalfa.

Little information is available regarding the performance of the CERES-Maize model under nemoral climate conditions. Therefore, this study aims to estimate and compare major soil-plant N cycle parameters in grain maize (Zea mays L.) crop after application of synthetic and different organic fertilizers solely or in combination in nemoral zone maize production, using the Decision Support System for Agrotechnology Transfer (DSSAT) model. Field experiments carried out during 2015, 2016, and 2017 in Akademija (Lithuania) were considered for model calibration and validation. The model was successfully validated for total aboveground biomass (TAB, R-2 = .89), grain yield (GY, R-2 = .85), and acceptably for leaf area index (LAI, R-2 = .57), total plant N uptake (R-2 = .61), and residual soil mineral N (R-2 = .64). The lower plant N uptake and soil mineral nitrogen (SMN) observed for the pelletized cattle manure (PCM) and green waste compost (GWC) treatments compared to the fertilization with synthetic ammonium nitrate (AN) were successfully captured by the model. Finally, the model provided reasonable predictions of the temporal dynamics of measured soil water content (SWC) and soil temperature. The validated model was further used to provide N loss estimations during the maize growing seasons via leaching and gaseous emissions. The results showed that the CERES-Maize model can successfully be used to simulate maize growth under the extreme climatic conditions of the nemoral zone in combination with different N managements. Nevertheless, additional efforts are needed to verify and fine-tune the model to comprehensively simulate the N cycle, especially losses by drainage water and gaseous( )emissions.

Aim of the study: The use of pig slurry as fertiliser is associated with gaseous nitrogen (N) losses, especially ammonia (NH3) and nitrous oxide (N2O), leading to environmental problems and a reduction of its fertiliser value. This study evaluates, in an irrigated wheat crop, the effect of different additives mixed with pig slurry to decrease NH3 and N2O losses.Area of study: Middle Ebro valley, SpainMaterials and methods: The treatments were: i) non-N-fertilised control, ii) pig slurry (PS), iii) pig slurry with the urease inhibitor monocarbamide dihydrogen sulphate (PS-UI), iv) pig slurry with a microbial activator in development (PS-A), and v) pig slurry with the nitrification inhibitor 3,4-dimethylpyrazole phosphate (PS-NI). Pig slurry was applied at a target rate of 120 kg NH4+-N ha-1. Ammonia volatilisation was measured using semi-opened static chambers after treatments application at presowing 2016 and side-dressing 2017. Nitrous oxide emissions were measured using static closed chambers after treatments application at the 2017 and 2018 side-dressing.Main results: Ammonia volatilisation was estimated to be 7-9% and 19-23% of NH4+-N applied after presowing and side-dressing applications, respectively. Additives were not able to reduce NH3 emissions in any application moment. PS-NI was the only treatment being effective in reducing N2O emissions, 70% respect to those in PS treatment. Crop yield parameters were not affected by the application of the additives because of the no effect of additives controlling NH3 losses and the low contribution of N2O losses to the N balance (<1 kg N2O-N ha-1).Research highlights: The use of 3,4-dimethylpyrazole phosphate would be recommended from an environmental perspective, although without grain yield benefits.

Using slurries as fertilizers is a promising strategy for the reuse of nutrients and striving towards a circular economy. This study aims to assess the agronomic productivity and the environmental effects on Mediterranean sprinkler-irrigated wheat during three consecutive years of (1) the use of pig slurry (PS) as a substitute for a synthetic fertilizer (urea, U) and (2) the addition of a urease inhibitor (monocarbamide dihydrogen sulfate, MCDHS) to pig slurry (PSI). A nitrogen (N) target rate of 120 kg NH4+-N ha−1 as U, PS, or PSI (main factor) was applied at tillering, and it was supplemented with N application at stem elongation (secondary factor). Grain yield, nitrogen use efficiency indexes, and nitrous oxide emissions were not significantly affected by the N source, U, or PS; in contrast to grain protein that was affected by the N source (lower protein content in PS). The higher unaccounted N from soil balance in PS compared to U fertilization could be associated with higher ammonia volatilization, although additional studies should confirm this hypothesis. Our study suggests that, under the considered cropping conditions, PS does not affect productivity or N2O losses compared to U. The addition of MCDHS to pig slurry did not display agronomic or environmental benefits under the evaluated agro-environmental conditions.

The gap between scientifically sound nitrogen (N) fertilizer application rates and the actual rates used by farmers in maize is still significant. The improvement of nitrogen use efficiency in such a highly N-demanding crop is necessary to decrease the negative effects of N fertilization. The objective was to compare the performance of different N management treatments in maize grown under semiarid Mediterranean sprinkler-irrigated conditions to the standard farmer practice. We compared an agronomically sound fixed rate of N fertilizer (FR) with a variable N rate obtained based on a soil mineral balance at pre-planting (SB) or based on a portable chlorophyll meter readings (CM) made just before tasseling. Additional treatments were a N control, without fertilizer (T0), and a non-limiting N (NL) treatment wich was typical of the current farmer practice. The study was replicated at 5 sites in one-year experiments and under 3 pre-planting soil mineral nitrogen environments (SMN, Low, Medium, and High). The results demonstrate the potential to reduce N rates from zero to 236 kg N ha(-1) compared to the NL in irrigated maize fields without compromising yields in most of the situations with a subsequent increase of NUE. Averaging over sites, the use of fine-tuning N fertilizer strategies that considered field-specific conditions (SB and CM) reduced N rates (38 %) compared to the reductions under the FR strategy (26 %) relative to the NL conditions, which is the treatment closest to a typical farmer's application rate.

Stabilised nitrogen (N) fertilisers with nitrification and urease inhibitors have been proposed to abate greenhouse gas (GHG) emissions in agrosystems. Nevertheless, differences in their application and in the management of water and nitrogen rates make it difficult to evaluate their actual utility. The aim of this study was to analyse the possibility for GHG emissions reduction in a 3-year rotation (maize-maize-wheat) by substituting the traditional split-urea application to maize by a single side-dress application of stabilised urea fertiliser. The experiment was performed in 24 drainage lysimeters in two contrasting soil types (Shallow and Deep) under efficient irrigation practices and adjusted N rates under Mediterranean conditions. Nitrous oxide (N2O) and methane (CH4) were measured using static closed unvented chambers, and the soil mineral N was monitored through periodic soil samplings. CH4 emissions were generally negligible with occasional tendency the soil acting as a sink more than as a net source. Direct N2O emissions during the whole rotation showed lower values when a nitrification inhibitor (3,4-dimethylpyrazole phosphate) was added than with conventional urea (Deep soil: 73% lower, p < 0.05; Shallow soil: 60% lower, ns). Urease inhibitors (N-(n-butyl) thiophosphoric triamide and monocarbamide dihydrogen sulphate) could not abate direct N2O emissions, and their effect depended on the soil type. However, all stabilised fertilisers mitigated N2O emissions in Deep soil when scaled by grain yield (average 54%). Indirect N2O emissions associated with nitrate leaching were not affected by the treatments but contributed more to total N2O emissions in Shallow soil (12%) than in Deep soil (6%). These results suggest that adequate use of nitrification inhibitors could have environmental benefits without lessening agronomic production.

Closed-chamber methodology is widely used for the estimation of greenhouse gas (GHG) emissions in agricultural systems. The volume displaced by plants inside chambers influences GHG flux estimation, although generally it is not discounted from chamber headspace in the calculation. A novel image analysis-based procedure is proposed to estimate plant volume and to assess its impact on nitrous oxide (N2 O) flux estimations in a wheat (Triticum aestivum L. 'Rimbaud') crop. A maximum of 2.2% of the 13-L chambers was displaced by plants, leading to a systematic 0.9% overestimation in cumulative N2 O emissions if plant volume was not considered. Thus, plant canopy volume should be taken into account for improving the accuracy of emissions.

Background:The inadequate application of nitrogen (N) to crops has increased the reactive N in the atmosphere and in the surface and ground waters. Stabilized N-fertilizers with nitrification (NI) and urease (UI) inhibitors have been proposed to reduce these environmental problems without affecting or even increasing crop productivity. Aim:The objective of this study was to evaluate, in a maize-maize-wheat rotation, if the use of the NI 3,4-dimethylpyrazole phosphate (DMPP) and the UIs N-(n-butyl) thiophosphoric triamide (NBPT) and monocarbamide dihydrogen sulfate (MCDHS) reduces N leaching without compromising yield under optimal management of N and water. Methods:The experiment was conducted in 24 drainage lysimeters with two soil types with contrasting water holding capacity under Mediterranean irrigated conditions. The fertilizer treatments were urea, urea with DMPP, urea with NBPT, and urea with MCDHS. For the maize crop, conventional fertilizer application was split into 6- and 13-leaf stages, whereas stabilized fertilizers were applied as a single application at the 6-leaf stage. All fertilizer treatments were applied at late tillering in the wheat crop. Results:The soil mineral N was measured at the beginning and the end of each crop season, but no differences were found among fertilizer treatments. Differences in the volume of water drained or the cumulative mass of nitrate depending on the fertilizer were not significant (three-year treatment average of 200 L m(-2)and 22 kg N ha(-1)in the Deep soil, and 334 L m(-2)and 40 kg N ha(-1)in the Shallow type, respectively). No consistent significant differences were found in agronomic parameters (chlorophyll measurements, yield, and total N uptake) between the fertilizer treatments. Conclusion:Based on the results, the use of stabilized N-fertilizer could be recommended to reduce the number of N applications in maize without compromising grain yield but with no advantages to reduce nitrate-leaching losses if N rates are managed properly under efficient irrigation management practices.

Este estudio ha sido financiado por el Ministerio de Economia, Industria y Competitividad (proyecto AGL2013-49062-C4-3-R). N. Mateo-Marin cuenta con un contrato predoctoral FPI-INIA-2015. Los fertilizantes con inhibidores fueron proporcionados por Compo Expert S.L., EuroChem Agro Iberia S.L. y Fertinagro Biotech S.L.

Maintain high agriculture production levels while reducing environmental impacts is of primordial importance in intensive irrigated areas. Adequate management of water and nitrogen are critical for a sustainable agriculture. The objectives of this work were to (i) calibrate and validate DSSAT model for maize under different nitrogen availability conditions and (ii) assess the effect of best management practices on irrigation water needs and nitrogen losses by leaching using different scenarios in an intensive irrigated area. For model calibration and validation, three field experiments were conducted with a total of 134 plots. Then, the model application was performed in three soil types in the 'Del Reguero' watershed (Spain) considering (i) real irrigation applied by farmers and DSSAT automatic irrigation and (ii) a recommended dose of N fertilizer (250 kg N ha(-1)) compared to a traditional dose of 390 kg N ha(-1). Among all plots, the model simulated reasonably well grain yield with a Root Mean Square Error (RMSE) lower than 708 kg ha(-1) and high Willmott agreement index (d statistic) ( > 0.9). Very similar trends were observed for total biomass and total N uptake with a RMSE of 2018 kg ha(-1) and 36.6 kg N ha(-1). The prediction of residual nitrate in soil was acceptable with a RMSE of 43 kg N ha(-1). Modeling results showed that adjusted irrigation would reduce (on average for different soil types) the total amount of seasonal irrigation water by 31% and the nitrate leaching by 97% without a significant reduction in grain yield. Regarding to N fertilizer scenarios, results showed that farmers can reduce the N fertilizer currently applied leading to a significant decrease in the N leached between 33 and 53% depending on soil types.

Core Ideas Soil GHG emissions were quantified in four fertilization scenarios in irrigated corn. Fertilization scenarios had minor effect on CO 2 and CH 4 emissions. Soil mineral N level affected N 2 O emissions and yield‐scaled N 2 O emissions. Agricultural soils emit greenhouse gases (GHG). Excessive application of N fertilizer may lead to the accumulation of mineral N in the soil, which is susceptible to loss to the environment. The objective of this study was to quantify the effect of two levels of available mineral N before planting (L, low; H, high) and two rates of NH 4 NO 3 fertilizer (0 and 300 kg N ha −1 ) on soil CH 4 , CO 2 , and N 2 O emissions in a sprinkler‐irrigated corn ( Zea mays L.) field located in northeastern Spain during two growing seasons (2011 and 2012). For both soil N levels at planting, several sampling dates showed higher N 2 O emissions in the 300 kg N ha −1 treatment than the 0 kg N ha −1 treatment. Applications of N fertilizer resulted in a short‐lived increase of N 2 O emitted. Differences among fertilization treatments were found for soil CO 2 emissions in 2011 and for soil N 2 O emissions in 2011 and 2012. No differences were found between treatments for CH 4 . In the 2012 season, the application of 300 kg N ha −1 in the L scenario reduced N 2 O yield‐scaled emissions (g N 2 O‐N kg −1 aboveground N uptake) by 30% due to a significant increase in corn yield (7.6 Mg grain ha −1 ) compared with the treatment without N. Conversely, under the H scenario, N application doubled yield‐scaled N 2 O emissions. Results of this study demonstrate that fertilization strategies need to take into account mineral N levels in the soil before sowing to reduce GHG emissions during the growing season.

There are limited studies about the effect of nitrogen (N) deficiency on leaf growth, N status, and photosynthetic capacity of maize grown under field conditions in a Mediterranean climate. The objective of this work was to evaluate the effect of different levels of mineral N availability on leaf gas exchange parameters of sprinkler irrigated maize. The experiment was conducted in a conventional maize field located in the central part of the Ebro valley (Spain) during two seasons. Using a portable LICOR-6400 equipment, instantaneous measurements and light response curves to gas exchange were conducted in plots with different levels of N supply ranging from deficient (no fertilized) to over-fertilized (300 kg N/ha). In addition to gas exchange measurements, mineral soil N content, chlorophyll meter readings (CMR), leaf N content, and grain yield were measured in the different plots. Results showed that grain yield reached a plateau (14.5 Mg/ha) when the mineral N available was about 179 kg/ha. CMR were linearly and highly related to total N in ear leaves. The relationship between light-saturated leaf photosynthesis measurements and CMR was significant but very weak (R-2=0.13) at V8 and V14 stages but increased later in the growing season (R-2=0.52). Plants with intermediate levels of N supply (48<CMR<54) tended to have slightly higher assimilation rates than plants with higher CMR readings. As the available N increased, the saturation point, the light compensation point and significant increases of dark respiration rate were observed. Under the conditions of the study, leaf N contents of 1.9% in the ear leaf were enough to maximize leaf assimilation rates with no need to over-fertilize the maize crop.

Se ha estudiado la respuesta del maiz a la fertilizacion nitrogenada tras un cultivo de alfalfa en siete experimentos de campo en regadios semiaridos del Valle del Ebro. Se aplicaron seis dosis de N (de 0 a 300 kg N/ha). La alfalfa proporciono suficiente N para producir de 10,3 a 16,7 Tm/ha de grano de maiz sin fertilizante nitrogenado. En tres de los ensayos no se necesito N fertilizante para obtener el maximo rendimiento de maiz. En el resto de los ensayos, la dosis optima de N fertilizante vario entre 115 y 196 kg N/ha, siendo menor en los ensayos regados por aspersion comparados con los regados por inundacion. El maximo retorno economico se obtuvo con dosis entre 0 y 150 kg N/ha. Dosis mayores de 150 kg N/ha aumentaron el riesgo de contaminacion ambiental sin aumentar el rendimiento ni el beneficio economico

Calibration of decision tools to improve N fertilizer management is critical to increase its adoption by maize (Zea mays L.) growers. The objective of this study was to establish nitrate and total nitrogen concentrations in the basal maize stalks (BMS) at harvest to separate maize fields among three N availability categories (N-deficient, N-optimum, and N-excess) under Mediterranean irrigated semiarid conditions. We analysed data from 26 irrigated maize trials conducted between 2001 and 2012. Trials included treatments receiving different N fertilizer rates and sources (mineral and organic), irrigation systems (flood, sprinkler) and soil types. The critical nitrate concentration in BMS to identify N-deficient plots (CNCL) is affected by the irrigation system. The CNCL was lower under sprinkler irrigation (708 mg NO3-­–N/kg) than under flood irrigation (2205 mg NO3-­–N/kg), and the later presented a higher degree of uncertainty compared to sprinkler irrigated systems. The results showed the difficulty to identify the N-deficient plots with the BMS test and the higher sensibility of nitrate-N than total-N concentration in BMS to separate N-deficient from N-optimal plots. Under sprinkler irrigation, nitrate in BMS>1500 mg NO3-­–N/kg had a 85% probability of having received an excess of N. Considering economic net returns to N fertilization, the range of nitrate concentration in BMS that maximized profit under sprinkler-irrigated conditions was established between 1100 and 1700 mg NO3-–N/kg. Results suggest that BMS test can be useful in detecting plots with an excess of N but considering irrigation efficiency is crucial for stablishing successful CNC thresholds.