Nitrapyrin addition mitigates nitrous oxide emissions and raises nitrogen use efficiency in plastic-film-mulched drip-fertigated cotton field

Enhanced efficiency nitrogen fertilizers were not effective in reducing N2O emissions from a drip-irrigated cotton field in arid region of Northwestern China

Drip irrigation is an effective water-saving strategy for crop production in arid regions. However, limited information is available on how fertilizer nitrogen (N) management affects soil nitrous oxide (N₂O) emission under drip irrigation. A two-year (2017-2018) field experiment was conducted in arid northwestern China to test management options of fertilizer N to reduce N₂O emission and improve NUE of cotton (Gossypium hirsutum L.) under drip irrigation. Treatment included a factorial design of rate (120, 240 kg N ha^-1) and source of N fertilizer (Urea, polymer-coated urea-ESN, stabilized urea with nitrification and urease inhibitors-SuperU), and an unfertilized Control. Urea was split-applied with irrigation water (fertigation) whereas ESN and SuperU were all side-banded at pre-plant. Crop yield and N uptake, soil mineral N concentrations, soil temperature and moisture, and N₂O fluxes were determined. Across the two growing seasons, a single pre-plant application with ESN or SuperU significantly increased growing season cumulative N₂O emissions (ƩN₂O) by 29-47% and applied N-scaled emission factor (EF) by 57-83% compared to urea fertigation, irrespectively of application rate. In contrast, cotton yield, agronomic NUE, apparent N recovery (ANR), and yield-based N₂O emission intensity (EI) were not affected by N source. Reducing N rate from 240 to 120 kg N ha^-1 significantly decreased ƩN₂O by 35% in 2017 and 36% in 2018 while simultaneously reduced cotton yield in both years. The increased N₂O emissions with ESN and SuperU were attributed to greater availability of inorganic N resulted from one-time application at pre-plant and higher soil temperature. We concluded that fertigation with urea at the recommended rate is the best option to ensure agronomic productively and agronomic NUE with minimal risk of N₂O emissions. In contrast, the benefit of enhanced efficiency N fertilizer is limited and recommendation on using of these products is challenging for arid croplands under drip irrigation.

Effect of N fertilizer types on N2O and NO emissions under drip fertigation from an agricultural field in the North China Plain

N₂O and NO emissions from a winter wheat-summer maize rotation field in the North China Plain were comparably investigated under three different treatments: 1) flood irrigation (A-Flood treatment) plus fertilization of NH₄Cl, 2) drip fertigation (A-Drip treatment) plus fertilization of NH₄Cl and 3) drip fertigation (AN-Drip treatment) plus fertilization of a mixture of Ca(NO₃)₂ and NH₄Cl. The annual N₂O cumulative emissions from the A-Drip treatment and the A-Flood treatment were almost identical, whereas it from the AN-Drip treatment was significantly lower (33%) than that from the A-Flood treatment. Compared with the A-Flood treatment, the annual NO cumulative emission from the A-Drip treatment was significantly increased by 140% but it from the AN-Drip treatment was only slightly increased by 14%. Compared with drip fertigation with NH₄Cl, drip fertigation with the mixture of Ca(NO₃)₂ and NH₄Cl significantly reduced the cumulative emissions of N₂O (31%) and NO (52%) from the nitrification dominated fields by decreasing the supplement of NH₄⁺ substrate. Among the three fertilization treatments, the yields of the maize from the A-Drip and AN-Drip treatments were significantly increased, while the yields of the wheat were almost the same. Considering the benefit of increasing yields and reducing N fertilizer and water input, the application of nitrate-based fertilizer instead of partial ammonium-based fertilizer through drip fertigation could be a promising method for keeping agronomic productivity and environmental sustainability.

Agronomic evaluation of polymer-coated urea and urease and nitrification inhibitors for cotton production under drip-fertigation in a dry climate

Interest in the use of enhanced-efficiency nitrogen (N) fertilizers (EENFs) has increased in recent years due to their potential to increase crop yield and reduce environmental N loss. Drip-fertigation is widely used for crop production in arid regions to improve water and nutrient use efficiency whereas the effectiveness of EENFs with drip irrigation remains unclear. A field experiment was conducted in 2015 and 2016 to examine the effects of EENFs on yield, N use and quality of cotton (Gossypium hirsutum) grown under drip-fertigation in arid NW China. Treatments included an unfertilized control and application of 240 kg N ha^-1 by polymer-coated urea (ESN), urea alone, or urea plus urease (NBPT) and nitrification (DCD) inhibitors. ESN was all banded in the plant row at planting, whereas urea was applied with 20% N banded at planting and 80% N by six fertigation events over the growing season. Results showed there was generally no treatment effect on seed and lint yield, N concentration or allocations, N recovery efficiency and fiber quality index of cotton. A lack of treatment effect could be due to N supplied with drip-fertigation better synthesized with crop N needs and the relatively high soil native NO₃^- availability, which hindered the effect of polymer-coated urea and double inhibitors. These results highlight the challenge of the employment of EENFs products for drip-fertigation system in arid area. Further research is required to define the field conditions under which the agronomic efficiency of EENFs products may be achieved in accordance with weather conditions.

Urea Nitrapyrin Placement Effects on Soil Nitrous Oxide Emissions in Claypan Soil

Corn ( L.) production in poorly drained claypan soils in the US Midwest is a challenge due to low soil permeability, which may result in wetter soil conditions and relatively large amounts of soil NO emissions early in the growing season. The objectives of this study were to determine the effects of urea fertilizer placement with and without nitrapyrin (NI) on daily and cumulative soil NO emissions, and yield-scaled NO emissions in 2016 and 2017. Treatments included urea deep banded to a 20-cm depth (DB), urea deep banded to 20 cm plus NI (DB+NI), urea incorporated after a surface broadcast application to ∼8-cm depth (IA), urea broadcast on the soil surface (SA), and a nonfertilized control (NTC). Fertilizer was applied at 202 kg N ha. Surface soil NO efflux rates were generally lower (<50 g NO-N ha d) during the first 3 wk after N fertilization and latter parts of the growing seasons. When averaged across the 2016 and 2017 growing seasons, all fertilized treatments had significantly greater (2.33-5.60 kg NO-N ha, < 0.05) cumulative soil NO emissions than NTC. The DB+NI treatment had 54 and 55% lower cumulative soil NO emissions than IA and SA, respectively. In 2017, DB+NI had similar soil yield-scaled NO emissions to NTC. Percentage grain yield increase over NTC was highest for DB and DB+NI. Grain yield in 2016 was 14 to 18% higher for DB and DB+NI than SA. Results suggest that DB+NI is an effective management strategy for reducing cumulative soil NO emissions and increasing grain yields over the growing season.

Abundance, rather than composition, of methane-cycling microbes mainly affects methane emissions from different vegetation soils in the Zoige alpine wetland

Methane fluxes, which are controlled by methanogens and methanotrophs, vary among wetland vegetation species. In this study, we investigated belowground methanogens and methanotrophs in two soils under two different dominant vegetation species with different methane fluxes in the Zoige wetland, which was slightly but significantly (p ≤ 0.05) higher in soils covered by Carex muliensis than that in soils covered by Eleocharis valleculosa. Real‐time quantitative PCR and Illumina MiSeq sequencing methods were used to elucidate the microbial communities based on the key genes involved in methane production and oxidation. The absolute abundances of methanogens and methanotrophs of samples from C. muliensis were 1.80 ± 0.07 × 10⁶ and 4.03 ± 0.28 × 10⁶ copies g‐soil⁻¹, respectively, and which from E. valleculosa were 3.99 ± 0.19 × 10⁵ and 2.53 ± 0.22 × 10⁶ copies g‐soil⁻¹ , respectively. The t‐test result showed that both the abundance of methanogens and methanotrophs from C. muliensis were significantly higher (p ≤ 0.05) than that of samples from E. valleculosa. However, the diversities and compositions of both methanogens and methanotrophs showed no significant differences (p ≥ 0.05) between vegetation species. The path analysis showed that the microbial abundance had a greater effect than the microbial diversity on methane production potentials and the regression analysis also showed that the methane emissions significantly (p ≤ 0.05) varied with the abundance of methane‐cycling microbes. These findings imply that abundance rather than diversity and composition of a methane‐cycling microbial community is the major contributor to the variations in methane emissions between vegetation types in the Zoige wetland.