Partial substitution of manure reduces nitrous oxide emission with maintained yield in a winter wheat crop

Conventional fertilization of agricultural soils results in increased N₂O emissions. As an alternative, the partial substitution of organic fertilizer may help to regulate N₂O emissions. However, studies assessing the effects of partial substitution of organic fertilizer on both N₂O emissions and yield stability are currently limited. We conducted a field experiment from 2017 to 2021 with six fertilizer regimes to examine the effects of partial substitution of manure on N₂O emissions and yield stability. The tested fertilizer regimes, were CK (no fertilizer), CF (chemical fertilizer alone, N 300 kg ha^-1, P₂O₅ 150 kg ha^-1, K₂O 90 kg ha^-1), CF + M (chemical fertilizer + organic manure), CFR (chemical fertilizer reduction, N 225 kg ha^-1, P₂O₅ 135 kg ha^-1, K₂O 75 kg ha^-1), CFR + M (chemical fertilizer reduction + organic manure), and organic manure alone (M). Our results indicate that soil N₂O emissions are primarily regulated by soil mineral N content in arid and semi-arid regions. Compared with CF, N₂O emissions in the CF + M, CFR, CFR + M, and M treatments decreased by 16.8%, 23.9%, 42.0%, and 39.4%, respectively. The highest winter wheat yields were observed in CF, followed by CF + M, CFR, and CFR + M. However, the CFR + M treatment exhibited lower N₂O emissions while maintaining high yield, compared with CF. Four consecutive years of yield data from 2017 to 2021 illustrated that a single application of organic fertilizer resulted in poor yield stability and that partial substitution of organic fertilizer resulted in the greatest yield stability. Overall, partial substitution of manure reduced N₂O emissions while maintaining yield stability compared with the synthetic fertilizer treatment during the wheat growing season. Therefore, partial substitution of manure can be recommended as an optimal N fertilization regime for alleviating N₂O emissions and contributing to food security in arid and semi-arid regions.

Nitrous oxide and methane emissions from soil under integrated farming systems in southern Brazil

This study aimed at evaluating soil nitrous oxide (N₂O) and methane (CH₄) emissions from integrated farming systems. Soil N₂O and CH₄ fluxes were assessed in a subtropical Cambisol in southern Brazil, using manual static chambers, over two years, in five farming systems (cropland, livestock, integrated crop-livestock, integrated livestock-forestry, and integrated crop-livestock-forestry). The study was conducted in four growing seasons: summer-1, winter-1, summer-2, winter-2. Integrated farming systems had lower soil N₂O emissions than livestock. The observed reduction was possibly due to lower water-filled pore space (WFPS) in soils under integrated systems (average 59.5-64.7%, vs 70.4% in livestock) as indicated by correlation (r = 0.74). Cropland, including cover-crops and maize, also had lower N₂O emission (by 40%) relative to livestock, of levels similar to those observed in integrated systems. Methane was consumed in soil, but it was not affected by farming systems, and offset only ~1.4% of the N₂O emissions. In the rainiest season of summer-2, the soil had the highest WFPS (on average 71.4%) and thus the highest N₂O emission (on average 9.79 kg N₂O-N ha^-1 season^-1) and the lowest CH₄ consumption (on average - 0.40 kg CH₄-C ha^-1 season^-1); while the opposite trend occurred in the driest season of winter-2 (on average 57.3% WFPS; 0.64 kg N₂O-N ha^-1 season^-1 and -0.90 kg CH₄-C ha^-1 season^-1). Integrated farming systems including crop-livestock, livestock-forestry and crop-livestock-forestry reduced soil N₂O emissions relative to sole livestock by 27-40%, but did not affect CH₄ emissions. Seasonal variations of precipitation, and therefore WFPS were driving factors of the N₂O and CH₄ emissions. Overall, integrated farming systems show the potential to mitigate soil N₂O emission compared to livestock system.

Biochar decreases the efficacy of the nitrification inhibitor nitrapyrin in mitigating nitrous oxide emissions at different soil moisture levels

Unprecedented increases in agricultural nitrous oxide (N₂O) emissions in recent years have caused substantial environmental pollution that leads to ozone depletion and global warming. Application of biochar and/or nitrification inhibitors (NIs) has the potential to reduce N₂O emissions; however, it is not clear how biochar application may affect the efficacy of NI in reducing nitrification rates, soil enzyme activities, and N₂O emissions under different soil moisture regimes. We conducted a 60-day laboratory incubation experiment to study the effects of manure biochar and nitrapyrin (as a NI) on N₂O emissions from a urea fertilized soil with either 60 (low) or 80% (high) water-filled pore space (WFPS). Nitrification rates were significantly affected by biochar × NI × WFPS and biochar × WFPS interactions. Biochar initially increased and then decreased the rates, resulting in 45.2 and 26.6% (P < 0.001 for both) overall reductions in low and high WFPS, respectively while NI reduced the rates only in the first 10 days at 60% WFPS. Biochar decreased (P < 0.001) and NI increased (P = 0.007) β-1,4-N-acetyl glucosaminidase activities while urease activities were increased (P < 0.001) by biochar across WFPS. Biochar had significant interaction with NI in cumulative N₂O emissions with the efficacy of NI being reduced when co-applied with biochar. Cumulative N₂O emissions were greater at high than at low WFPS; the emissions were decreased by biochar at 60% WFPS and NI at both 60 and 80% WFPS. We conclude that biochar reduces efficacy of nitrapyrin in mitigating N₂O emissions and their effects on net nitrification rates, enzyme activities and N₂O emissions are dependent on soil moisture level.

Deficit irrigation effectively reduces soil carbon dioxide emissions from wheat fields in Northwest China

BACKGROUND

An irrigation regime is an important factor in regulating soil CO₂ emissions from wheat fields. Deficit irrigation can be applied easily in the fields and has been implemented in northwest China. Previous studies have mainly focused on the effects of deficit irrigation on crop yield and quality. Studies on its environmental impacts are sparse.

RESULTS

Soil CO₂ fluxes from deficit-irrigated fields were lower than those from full irrigation (CK) during most of the growing season. Cumulative soil CO₂ emissions from deficit-irrigated fields were reduced by 10.2-25.5%, compared with the CK. Peaks of soil CO₂ fluxes were observed 3-7 days after irrigation in the water-filled pore space (WFPS) range of 65.7-80.4%. Under different irrigation regimes, significant positive correlations were observed between soil CO₂ fluxes and WFPS (P < 0.01), but no significant correlations were found between soil CO₂ fluxes and soil temperature. Compared to CK, yields for the T1, T2, and T4 were significantly reduced (P < 0.05) but the yield for T3 was only reduced by 2.3% (P > 0.05); T3 significantly reduced soil CO₂ emissions by 10.2% (P < 0.05) and reduced the irrigation water amount by 5.7%.

CONCLUSION

Deficit irrigation effectively reduced CO₂ emissions from winter wheat field soils. T3 may be a water-saving, CO₂ emission-reducing and high-yield irrigation regime for winter wheat fields in northwest China. The research laid a preliminary theoretical foundation for formulating winter wheat irrigation systems that are water saving, emission reducing, and that produce high yields. © 2019 Society of Chemical Industry.

Understanding the hydrologic control of N cycle: Effect of water filled pore space on heterotrophic nitrification, denitrification and dissimilatory nitrate reduction to ammonium mechanisms in unsaturated soils

Irrigation practice will be effective if it supplies optimal water and nutrients to crops and act as a filter for contaminants leaching to ground water. There is always a scope for improving the fertilizer use efficiency and scheduling of wastewater irrigation if the fate and transport of nutrients particularly nitrogenous compounds in the soil are well understood. In the present study, nitrogen transport experiments for two different agricultural soils are performed under varying saturation 33, 57, 78% water filled pore space for sandy soil 1 and 52, 81 and 96% for loam soil 2. A HYDRUS 2D model with constructed wetland (CW2D) module could simulate aerobic nitrification and anoxic denitrification well for both soils and estimated the reaction kinetics. A hot spot of Dissimilatory Nitrate Reduction to Ammonium (DNRA) pathway has been observed at 81% moisture content for a loamy sand soil. The presence of high organic content and reductive soil environment (5.53 C/NO₃^- ratio; ORP=-125mV) results in ammonium accumulation of 16.85mg in the soil. The overall observation from this study is nitrification occurs in a wide range of saturations 33-78% with highest at 57% whereas denitrification is significant at higher water saturations 57-78% for sandy soil texture. For a loamy sand soil, denitrification is dominant at 96% saturation with least nitrification at all saturation studies. The greatest nitrogen losses (>90%) was observed for soil 2 while 30-70% for soil1. The slow dispersive subsurface transport with varying oxygen dynamics enhanced nitrogen losses from soil2 due to lesser soil permeability. This in turn, prevents NO₃^- leaching and groundwater contamination. This type of modeling study should be used before planning field experiments for designing optimal irrigation and fertigation schedules.

Modelling the interactions between C and N farm balances and GHG emissions from confinement dairy farms in northern Spain

There is world-wide concern for the contribution of dairy farming to global warming. However, there is still a need to improve the quantification of the C-footprint of dairy farming systems under different production systems and locations since most of the studies (e.g. at farm-scale or using LCA) have been carried out using too simplistic and generalised approaches. A modelling approach integrating existing and new sub-models has been developed and used to simulate the C and N flows and to predict the GHG burden of milk production (from the cradle to the farm gate) from 17 commercial confinement dairy farms in the Basque Country (northern Spain). We studied the relationship between their GHG emissions, and their management and economic performance. Additionally, we explored some of the effects on the GHG results of the modelling methodology choice. The GHG burden values resulting from this study (0.84-2.07 kg CO2-eq kg(-l) milk ECM), although variable, were within the range of values of existing studies. It was evidenced, however, that the methodology choice used for prediction had a large effect on the results. Methane from the rumen and manures, and N2O emissions from soils comprised most of the GHG emissions for milk production. Diet was the strongest factor explaining differences in GHG emissions from milk production. Moreover, the proportion of feed from the total cattle diet that could have directly been used to feed humans (e.g. cereals) was a good indicator to predict the C-footprint of milk. Not only were some other indicators, such as those in relation with farm N use efficiency, good proxies to estimate GHG emissions per ha or per kg milk ECM (C-footprint of milk) but they were also positively linked with farm economic performance.