Inhibitory Effects of 3,4-Dimethylpyrazole Phosphate on CH4 and N2O Emissions in Paddy Fields of Subtropical China

A global meta-analysis of yield-scaled N2 O emissions and its mitigation efforts for maize, wheat, and rice

Maintaining or even increasing crop yields while reducing nitrous oxide (N2 O) emissions is necessary to reconcile food security and climate change, while the metric of yield-scaled N2 O emission (i.e., N2 O emissions per unit of crop yield) is at present poorly understood. Here we conducted a global meta-analysis with more than 6000 observations to explore the variation patterns and controlling factors of yield-scaled N2 O emissions for maize, wheat and rice and associated potential mitigation options. Our results showed that the average yield-scaled N2 O emissions across all available data followed the order wheat (322 g N Mg-1 , with the 95% confidence interval [CI]: 301-346) > maize (211 g N Mg-1 , CI: 198-225) > rice (153 g N Mg-1 , CI: 144-163). Yield-scaled N2 O emissions for individual crops were generally higher in tropical or subtropical zones than in temperate zones, and also showed a trend towards lower intensities from low to high latitudes. This global variation was better explained by climatic and edaphic factors than by N fertilizer management, while their combined effect predicted more than 70% of the variance. Furthermore, our analysis showed a significant decrease in yield-scaled N2 O emissions with increasing N use efficiency or in N2 O emissions for production systems with cereal yields >10 Mg ha-1 (maize), 6.6 Mg ha-1 (wheat) or 6.8 Mg ha-1 (rice), respectively. This highlights that N use efficiency indicators can be used as valuable proxies for reconciling trade-offs between crop production and N2 O mitigation. For all three major staple crops, reducing N fertilization by up to 30%, optimizing the timing and placement of fertilizer application or using enhanced-efficiency N fertilizers significantly reduced yield-scaled N2 O emissions at similar or even higher cereal yields. Our data-driven assessment provides some key guidance for developing effective and targeted mitigation and adaptation strategies for the sustainable intensification of cereal production.

Combined application of biochar with urease and nitrification inhibitors have synergistic effects on mitigating CH4 emissions in rice field: A three-year study

Biochar and inhibitors applications have been proposed for mitigating soil greenhouse gas emissions. However, how biochar, inhibitors and the combination of biochar and inhibitors affect CH₄ emissions remains unclear in paddy soils. The objective of this study was to explore the effects of biochar application alone, and in combination with urease (hydroquinone) and nitrification inhibitors (dicyandiamide) on CH₄ emissions and yield-scaled CH₄ emissions during three rice growing seasons in the Taihu Lake region (Suzhou and Jurong), China. In Suzhou, N fertilization rates of 120-280 kg N ha^-1 increased CH₄ emissions compared to no N fertilization (Control) (P < 0.05), and the highest emission was observed at 240 kg N ha^-1, possibly due to the increase in rice-derived organic carbon (C) substrates for methanogens. Biochar amendment combined with N fertilization reduced CH₄ emissions by 13.2-27.1% compared with optimal N (ON, Suzhou) and conventional N application (CN-J, Jurong) (P < 0.05). This was related to the reduction in soil dissolved organic C and the increase in soil redox potential. Addition of urease and nitrification inhibitor (ONI) decreased CH₄ emissions by 15.7% compared with ON treatment. Combined application of biochar plus urease, nitrification and double inhibitors further decreased CH₄ emissions by 22.2-51.0% compared with ON and CN-J treatment. ON resulted in the highest yield-scaled CH₄ emissions, while combined application of biochar alone and in combination with the inhibitors decreased yield-scaled CH₄ emissions by 12.7-54.9% compared with ON and CN-J treatment (P < 0.05). The lowest yield-scaled CH₄ emissions were observed under combined application of 7.5 t ha^-1 biochar with both urease and nitrification inhibitors. These findings suggest that combined application of biochar and inhibitors could mitigate total CH₄ and yield-scaled CH₄ emissions in paddy fields in this region.