Impacts of Enhanced-Efficiency Nitrogen Fertilizers on Greenhouse Gas Emissions in a Coastal Plain Soil under Cotton

Enhanced-efficiency nitrogen fertilizer provides a reliable option for mitigating global warming potential in agroecosystems worldwide

Enhanced-efficiency nitrogen fertilizer (EENF), developed to improve synchronization between crop nitrogen demand and nitrogen supply, can guarantee global food security and mitigate nitrogen fertilizer-induced environmental consequences. However, comprehensive assessments of how EENF affects CH4 and CO2 emissions from paddies and drylands and the associated benefits are lacking. Here, we present the results of a global meta-analysis conducted to assess the above issues. Our results showed that, on average, applying nitrification inhibitors and coated controlled-release urea to paddy fields significantly decreased CH4 emissions by 24.0 % and 25.3 %, respectively, likely due to the weakened inhibition of NH4+ on CH4 oxidation. A similar effect on CO2 emission was observed when farmers used nitrification inhibitors and coated controlled-release urea in the drylands. The meta-analysis results revealed that all EENF products could help mitigate the global warming potential of paddies and drylands. After incorporating the benefit of global warming potential mitigation into the cost-benefit analysis, coated controlled-release urea application in paddies and drylands produced the largest environmental gains of $ 76.34 ha-1 and $ 79.35 ha-1, respectively. However, the relatively lower purchasing cost and larger yield increase of urease inhibitors resulted in the largest net profits for farmers. Moreover, a greater economic return was generally achieved by applying EENF to paddy fields than by applying EENF to drylands. These findings highlight the role of EENF in mitigating the global warming potential of global paddy and dryland fields, which has facilitated the comprehensive recognition of EENF-induced impacts.

Intercropping kura clover with prairie cordgrass mitigates soil greenhouse gas fluxes

Prairie cordgrass (PCG) (Spartina pectinata Link) has a high tolerance to soil salinity and waterlogging, therefore, it can thrive on marginal lands. Optimizing the nitrogen (N) input is crucial to achieving desirable biomass production of PCG without negatively impacting the environment. Thus, this study was based on the hypothesis that the use of legumes such as kura clover (Trifolium ambiguum M. Bieb.) (KC) as an intercrop with PCG can provide extra N to the crop reducing the additional N fertilizer and mitigating soil surface greenhouse gas (GHG) emissions. Specific objective of the study was to assess the impact of PCG managed with different N rates [0 kg N ha⁻¹ (PCG-0N), 75 kg N ha⁻¹ (PCG-75N), 150 kg N ha⁻¹ (PCG-150N), and 225 kg N ha⁻¹ (PCG-255N)], and PCG intercropped with KC (PCG-KC) on GHG fluxes and biomass yield. The experimental site was established in 2010 in South Dakota under a marginally yielding cropland. The GHG fluxes were measured from 2014 through 2018 growing seasons using the static chamber. Net global warming potential (GWP) was calculated. Data showed that cumulative CH₄ and CO₂ fluxes were similar for all the treatments over the study period. However, the PCG-KC, PCG-0N, and PCG-75N recorded lower cumulative N₂O fluxes (384, 402, and 499 g N ha⁻¹, respectively) than the PCG-150N (644 g N ha⁻¹) and PCG-255N (697 g N ha⁻¹). The PCG-KC produced 85% and 39% higher yield than the PCG-0N in 2016 and 2017, respectively, and similar yield to the other treatments (PCG-75N, PCG-150N, and PCG-255N) in these years. Net GWP was 52% lower for the PCG-KC (112.38 kg CO₂-eq ha⁻¹) compared to the PCG-225N (227.78 kg CO₂-eq ha⁻¹), but similar to other treatments. Soil total N was 15%% and 13% higher under PCG-KC (3.7 g kg⁻¹) than that under PCG-0N (3.2 g kg⁻¹) and PCG-75N (3.3 g kg⁻¹), respectively. This study concludes that intercropping prairie cordgrass with kura clover can enhance biomass yield and reduce fertilizer-derived N₂O emissions and net global warming potential.

Environmentally friendly fertilizers: A review of materials used and their effects on the environment

Fertilizer plays an important role in maintaining soil fertility, increasing yields and improving harvest quality. However, a significant portion of fertilizers are lost, increasing agricultural cost, wasting energy and polluting the environment, which are challenges for the sustainability of modern agriculture. To meet the demands of improving yields without compromising the environment, environmentally friendly fertilizers (EFFs) have been developed. EFFs are fertilizers that can reduce environmental pollution from nutrient loss by retarding, or even controlling, the release of nutrients into soil. Most of EFFs are employed in the form of coated fertilizers. The application of degradable natural materials as a coating when amending soils is the focus of EFF research. Here, we review recent studies on materials used in EFFs and their effects on the environment. The major findings covered in this review are as follows: 1) EFF coatings can prevent urea exposure in water and soil by serving as a physical barrier, thereby reducing the urea hydrolysis rate and decreasing nitrogen oxide (NO_x) and dinitrogen (N₂) emissions, 2) EFFs can increase the soil organic matter content, 3) hydrogel/superabsorbent coated EFFs can buffer soil acidity or alkalinity and lead to an optimal pH for plants, and 4) hydrogel/superabsorbent coated EFFs can improve water-retention and water-holding capacity of soil. In conclusion, EFFs play an important role in enhancing nutrients efficiency and reducing environmental pollution.

Nitrogen Management Affects Nitrous Oxide Emissions under Varying Cotton Irrigation Systems in the Desert Southwest, USA

Irrigation of food and fiber crops worldwide continues to increase. Nitrogen (N) from fertilizers is a major source of the potent greenhouse gas nitrous oxide (NO) in irrigated cropping systems. Nitrous oxide emissions data are scarce for crops in the arid western United States. The objective of these studies was to assess the effect of N fertilizer management on NO emissions from furrow-irrigated, overhead sprinkler-irrigated, and subsurface drip-irrigated cotton ( L.) in Maricopa, AZ, on Trix and Casa Grande sandy clay loam soils. Soil test- and canopy-reflectance-based N fertilizer management were compared. In the furrow- and overhead sprinkler-irrigated fields, we also tested the enhanced efficiency N fertilizer additive Agrotain Plus as a NO mitigation tool. Nitrogen fertilizer rates as liquid urea ammonium nitrate ranged from 0 to 233 kg N ha. Two applications of N fertilizer were made with furrow irrigation, three applications under overhead sprinkler irrigation, and 24 fertigations with subsurface drip irrigation. Emissions were measured weekly from May through August with 1-L vented chambers. NO emissions were not agronomically significant, but increased as much as 16-fold following N fertilizer addition compared to zero-N controls. Emission factors ranged from 0.10 to 0.54% of added N fertilizer emitted as NO-N with furrow irrigation, 0.15 to 1.1% with overhead sprinkler irrigation, and <0.1% with subsurface drip irrigation. The reduction of NO emissions due to addition of Agrotain Plus to urea ammonium nitrate was inconsistent. This study provides unique data on NO emissions in arid-land irrigated cotton and illustrates the advantage of subsurface drip irrigation as a low NO source system.