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An increasing area of oilseed rape cultivation in Europe is used to produce biodiesel. However, a large amount of straw residue is often left in the field in autumn. Straw mineralization provides both carbon (C) and nitrogen (N) sources for emission of soil nitrous oxide (N2O), which is an important greenhouse gas with a high warming potential. Some studies have focused on soil N2O emissions immediately post‐harvest; however, straw mineralization could possibly last over winter. Most field studies in winter have focused on freeze‐thaw cycles. It is still not clear how straw mineralization affects soil N2O emissions in unfrozen wintertime conditions. We carried out a field experiment in northern Germany in winter 2014, adding straw and glucose as a source of C with three rates of N fertilizer (0, 30, and 60 kg N ha−1). During the 26 days of observation, cumulative N2O emission in treatments without C addition was negative at all N fertilizer levels. Straw addition produced –3.2, 11.2, and 5.0 mg N2O‐N m−2 at 0, 30, and 60 kg N ha−1, respectively. Addition of glucose surprisingly caused –1.5, 74.6, and 165 mg N2O–N m−2 at 0, 30, and 60 kg N ha−1, respectively. This study demonstrates that oilseed rape straw does not cause high N2O emissions in wintertime when no extreme precipitation or freeze‐thaw cycles are involved, and soil organic C content is low. However, N2O emission could be intensively stimulated, when both easily available organic C and nitrate are not limited and the soil temperature between 0 and 10°C. These results provide useful information on potential changes to N2O emissions that may occur due to the increased use of oilseed rape for biodiesel combined with less severe winters in the northern hemisphere driven by global warming. [ABSTRACT FROM AUTHOR]

Under the hot and moist conditions of irrigated agriculture in the arid subtropics, turnover of organic matter is high, which can lead to considerable carbon (C) and nitrogen (N) losses. Therefore, sustainable use of these soils requires regular manure application at high rates. To investigate the contribution of consecutive manure applications to an arid sandy soil to various soil N pools, goat manure was isotopically labeled by feeding 15N‐enriched Rhodes grass hay and applied to the soil during a two‐year field experiment. In the first year, soils received 15N‐labeled manure to distinguish between soil‐derived and manure‐derived N. In the second year, these plots were split for the application of either 15N‐labeled or unlabeled manure to discriminate N derived from previous (first year) and recent (second year) manure application. Soil samples (of control and 15N‐manured soil) were collected at the end of the first and the second year, and incubated in two laboratory experiments with labeled or unlabeled manure. At the beginning of Experiment 1, 7% of total N, 11% of K2SO4 extractable N, and 16% of microbial biomass N were derived from previously field‐applied manure. While the application of manure during incubation increased microbial biomass N by 225% and 410% in the control soil and the previously field‐manured soil, respectively, N2O emissions were more affected on the control soil, releasing considerable amounts of the soil N‐pool (80% of total emissions). In Experiment 2, 4% of total N, 7% of K2SO4 extractable N, and 7% of microbial biomass N derived from previously applied manure, and 4%, 8%, and 3% from recently applied manure, respectively. Microbial biomass N and N2O‐N derived from manure declined with time after manure application, whereas in Experiment 1 this tendency was only observed for microbial biomass N. [ABSTRACT FROM AUTHOR]

Chemical composition of root and shoot litter controls decomposition and, subsequently, C availability for biological nitrogen transformation processes in soils. While aboveground plant residues have been proven to increase N2O emissions, studies on root litter effects are scarce. This study aimed (1) to evaluate how fresh maize root litter affects N2O emissions compared to fresh maize shoot litter, (2) to assess whether N2O emissions are related to the interaction of C and N mineralization from soil and litter, and (3) to analyze changes in soil microbial community structures related to litter input and N2O emissions. To obtain root and shoot litter, Maize plants (Zea mays L.) were cultivated with two N fertilizer levels in a greenhouse and harvested. A two-factorial 22-day laboratory incubation experiment was set up with soil from both N levels (N1, N2) and three litter addition treatments (Control, Root, Root+Shoot). We measured hourly CO2 and N2O fluxes, analyzed soil nitrate and water extractable organic C (WEOC) concentrations, and determined quality parameters of maize litter. Bacterial community structures were analyzed using 16S rRNA gene sequencing. Maize litter quality controlled NO3− and WEOC availability and decomposition related CO2 emissions. High bioavailability of maize shoot litter strongly increased CO2 and N2O emissions, while emissions induced by maize root litter remained low. We identified a strong positive correlation between cumulative CO2 and N2O emissions, supporting our hypothesis that litter quality affects denitrification by creating plant litter associated anaerobic microsites. The interdependency of C and N availability was validated by analyses of regression. Moreover, there was a strong positive interaction between soil NO3− and WEOC concentration resulting in much higher N2O emissions, when both NO3− and WEOC were available. A significant correlation was observed between total CO2 and N2O emissions, the soil bacterial community composition and the litter level, showing a clear separation of Root+Shoot samples of all remaining samples. Bacterial diversity decreased with higher N level and higher input of easily available C. Altogether, changes in bacterial community structure reflected degradability of maize litter with easily degradable C from maize shoot litter favoring fast growing C cycling and N reducing bacteria of the phyla Actinobacteria, Chloroflexi, Firmicutes and Proteobacteria. [ABSTRACT FROM AUTHOR]

Abstract: Nitrogen (N) surpluses from fertilizer application can cause major environmental harm including pollution of surface water, groundwater, and air. To assess such negative externalities, N balances are a complex but useful tool to predict surpluses and to measure effects of nutrient optimization strategies in agriculture. The Yaqui Valley in north‐western Mexico is representative for thousands of square kilometres of intensive, irrigated wheat production under arid conditions worldwide and has been targeted for conservation agriculture in recent years. For these cropping systems, detailed N balances are scarce and often incomplete. To help fill this knowledge gap, data from a long‐term experiment were collected in 2013/14 on a Vertisol to examine the impact of three tillage‐straw management practices (CTB: conventionally tilled beds; PB‐straw: permanent raised beds with residue retention; PB‐burn: permanent raised beds with residue burning) on N dynamics. Tillage had significant effects on soil NO3‐N, NH4‐N, and total N contents across the cropping period. Soil total N content was at all sampling depths lowest in CTB. Soil NO3‐N in the 0–90 cm profile was highest in PB‐burn over the cropping period and ranged from 77 kg ha−1 in the bed before pre‐planting fertilizer application up to 269 kg ha−1 in the furrow after the second fertilizer application. Annual simple N balances were +59 kg N ha−1 in CTB, +39 kg N ha–1 in PB‐straw, and +46 kg N ha−1 in PB‐burn. Residual mineral soil N was significantly affected by tillage‐straw management and lowest for PB‐straw (+205 kg N ha−1) and highest for CTB, and for PB‐burn (+283 kg N ha−1 each) in the 0–90 cm soil profile. Soil NO3‐N moved out of the effective wheat root zone, as indicated by the high residual NO3‐N content at 30–90 cm depth, which is an important pathway of N leaching. Quantifiable N losses through leaching and volatilization averaged 100 kg N ha−1. Our findings suggest that there is potential for substantial reductions in N inputs in all tillage‐straw systems to decrease N losses and to reduce mineral residual soil N, but care should be taken to avoid reducing grain protein content, which in PB straw was already below the quality standard. A knowledge transfer of the European “Nmin” concept is advisable in this region to regulate N fertilizer over‐application. [ABSTRACT FROM AUTHOR]

Herbivory and resource availability interactively regulate plant growth, biomass allocation, and production. However, the compensatory growth of plants under grazing intensities and manipulated environmental conditions is not well understood. A 2-year experiment with water (unirrigated and irrigated) and nitrogen fertilizer (0 and 75 kg N ha −1 year −1 ) addition was conducted at sites with 4 grazing intensities (0–7 sheep ha −1 ) in an annually rotational grazing system in Inner Mongolia. In this study, grazing had no significant effect on aboveground net primary production (ANPP) and net primary production (NPP). However, high grazing intensity strongly reduced the fraction of belowground net primary production to NPP. Water and nitrogen additions significantly increased ANPP by 39% and by 23%, respectively, but had no effect on belowground net primary production. ANPP showed lower response to nitrogen addition at high grazing intensity sites than at low grazing intensity sites. We found no evidence for grazing optimization on primary production of semiarid steppe, regardless of resource supplementations. Grazed plants minimized the reduction of ANPP by altering allocation priority and morphological traits. Our study highlights the “whole-plant” perspective when studying plant–herbivore interactions. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) emissions from agriculture demand attention because they are the main source of total global anthropogenic N2O-emissions. High N-fertilization and soil compaction are important factors that increase N2O-emissions. On intensively managed grassland sites both factors occur. Knowledge of the interaction of high N-fertilization and simultaneous soil compaction on N2O-emissions is therefore essential, but previous studies about this scenario are rare. In the presented study, N-fertilized grass swards (G) and unfertilized lucerne-grass mixtures (LG) were compared over a three-year period (2006-2008): N2O-emissions and dry matter yield were measured as a function of N-fertilization (0 (LG), 360 kg N ha-1 yr-1 (G) as CAN) and soil compaction (0 (C0), 321 kPa (C321)) on a loamy stagnic Luvisol derived from glacial till in northern Germany. CO2-equivalents (CO2eq) per hectare and per unit metabolizable energy (GJ ME) were calculated. N2O-emissions were significantly influenced by the interaction N-fertilization x soil compaction; emissions increased significantly when both factors were induced simultaneously (G/C0: 8.74, LG/C0: 2.46, G/C321: 13.31 and LG/C321: 2.22 kg N2O-N ha-1, respectively). Concerning the specific CO2-emissions, expressed in CO2eq (GJ ME)-1, the N-fertilized G swards emitted 67% more CO2eq than LG swards assuming that 50% of the field plots were compacted due to heavy wheel traffic, which are reliable figures from agricultural practice. Neither dry matter (DM) yield nor forage quality (MJ ME (kg DM)-1) differed significantly between fertilized G and unfertilized LG swards. Hence, legume-based instead of fertilizer-based forage production is a promising mitigation option without significant reduction of DM yields. In addition, results regarding soil compaction effects on GHG-emissions emphasize the urgent need to implement controlled traffic systems on intensively managed grassland in order to reduce the area affected by heavy wheel traffic. [ABSTRACT FROM AUTHOR]

Winter oilseed rape ( Brassica napus L., WOSR) is the major oil crop cultivated in Europe. Rapeseed oil is predominantly used for production of biodiesel. The framework of the European Renewable Energy Directive requires that use of biofuels achieves GHG savings of at least 50% compared to use of fossil fuel starting in 2018. However, N 2 O field emissions are estimated using emission factors that are not specific for the crop and associated with strong uncertainty. N 2 O field emissions are controlled by N fertilization and dominate the GHG balance of WOSR cropping due to the high global warming potential of N 2 O. Thus, field experiments were conducted to increase the data basis and subsequently derive a new WOSR-specific emission factor. N 2 O emissions and crop yields were monitored for three years over a range of N fertilization intensities at five study sites representative of German WOSR production. N 2 O fluxes exhibited the typical high spatial and temporal variability in dependence on soil texture, weather and nitrogen availability. The annual N 2 O emissions ranged between 0.24 kg and 5.48 kg N 2 O-N ha −1 a −1 . N fertilization increased N 2 O emissions, particularly with the highest N treatment (240 kg N ha −1 ). Oil yield increased up to a fertilizer amount of 120 kg N ha −1 , higher N-doses increased grain yield but decreased oil concentrations in the seeds. Consequently oil yield remained constant at higher N fertilization. Since, yield-related emission also increased exponentially with N surpluses, there is potential for reduction of the N fertilizer rate, which offers perspectives for the mitigation of GHG emissions. Our measurements double the published data basis of annual N 2 O flux measurements in WOSR. Based on this extended dataset we modeled the relationship between N 2 O emissions and fertilizer N input using an exponential model. The corresponding new N 2 O emission factor was 0.6% of applied fertilizer N for a common N fertilizer amount under best management practice in WOSR production (200 kg N ha −1 a −1 ). This factor is substantially lower than the linear IPCC Tier 1 factor (EF1) of 1.0% and other models that have been proposed. [ABSTRACT FROM AUTHOR]

Abstract: In the system of “aerobic rice”, especially adapted aerobic rice varieties are grown under non-flooded conditions in non-puddled and aerobic soils with supplemental irrigation and moderate external inputs. Limited research has been done so far on optimizing nutrient management to produce high yields. In this study, we investigated yield formation and dry matter translocation of aerobic rice cultivar HD297 in response to N application, grown under different irrigation regimes at two sites close to Beijing, North China. At the “experimental farm”, the groundwater table depth was 0.2–1m; at the “experimental station”, it was deeper than 2m. Fertilizer-N rates were 0, 75, and 150kgNha−1 applied in split dressings according to regional recommendations for lowland rice, with 30% being applied at sowing, 40% at tillering, and 30% at panicle initiation. The application of N increased grain yields from 3.4 to 4.4tha−1. There was no interaction between N rates and water management, and no effect of water treatment on the grain yield. Before anthesis, dry matter accumulation increased with N application, but after anthesis, it decreased with increasing N application. With high N applications, grain filling was limited by a low contribution of post-anthesis assimilates. This indicates that traditional lowland rice fertilizer application schedules are not suitable for aerobic rice. N rate and timing of N fertilizer should be adjusted to balance crop''s demand before and after anthesis. Reducing N before anthesis and applying N at anthesis is necessary to increase post-anthesis dry matter accumulation and finally grain yield. Furthermore, germplasm improvement is suggested to increase the translocation of dry matter to grain for increasing grain yield. On average, yield was 14% higher at the “experimental farm” than at the “experimental station”. Differences in crop growth and Mn uptake between the farm and the station mainly resulted from the difference in hydrology. In target areas for aerobic rice with a deep groundwater table more research is needed to determine whether Mn deficiency is a potential cause of yield suppression of aerobic rice. [Copyright &y& Elsevier]

Nitrogen fertilizers are the major source of nitrous oxide (N 2 O) emissions from arable land. The addition of nitrification inhibitors to fertilizers may improve the nitrogen (N) use efficiency and reduce N 2 O emissions. However, it is still unclear how crop rotations affect nitrification and urease inhibitors to reduce N 2 O emissions. We conducted a field experiment with two-year winter wheat and one-year oilseed rape cultivation in Germany from 2016 to 2017. We applied five different fertilizer treatments: (1) a control treatment without fertilization (N0); (2) calcium ammonium nitrate (CAN); (3) ammonium sulfate nitrate with the nitrification inhibitor 3,4-dimethylepyrazole phosphate (ENTEC); (4) urea; and (5) urea with the urease inhibitor N -(n -butyl) thiophosphoric triamide (UTEC). Crop yield, grain and straw N content, and N 2 O fluxes were measured to assess yield-scaled N 2 O emissions under different treatments. We found that in all fertilized treatments, the aboveground N uptake of wheat after wheat was 199–203 kg N ha−1, which was much lower than that of wheat after oilseed rape (252–271 kg N ha−1). The apparent N recovery of oilseed rape (13–23%) was much lower than in wheat after wheat (63–66%). The enhanced-efficiency fertilizers increased aboveground N uptake by 0–5% compared to fertilizers without inhibitors. The oilseed rape field had the highest yield-scaled N 2 O emissions (18.0, 15.1, 16.7 and 15.6 g N 2 O-N kg−1 aboveground N uptake in CAN, ENTEC, urea and UTEC, respectively). These results indicate that urease and nitrification inhibitors hold the potential to increase crop yield and reduce N 2 O emissions. Oilseed rape straw should be carefully managed to avoid high N 2 O emissions. Future research should be focused on different fertilizer level and optimized N application strategy to increase the efficiency of urease and nitrification inhibitors, for instance, by increasing the N application rate in wheat after wheat, but reducing it in oilseed rape. • Effect of NBPT and DMPP on grain yield is minor. • NBPT and DMPP hold the potential to reduce N 2 O emissions in winter wheat and oilseed rape fields. • In oilseed rape, N fertilization induced high post-harvest N 2 O emissions. [ABSTRACT FROM AUTHOR]