Nitrous oxide (N2​O) is a potent greenhouse gas, contributing roughly 7% to overall global warming, and its concentration in the atmosphere has reached the highest documented level in over 800,000 years. Agricultural systems, largely through the use of nitrogen (N) fertilizers, are responsible for a massive annual release of N2​O. A conventional approach to reducing emissions involves optimizing N application methods, but the timing of N application has been somewhat overlooked. Delayed N application, where fertilizer is applied later in the crop cycle, is an approach that aligns N supply with the critical N demand phase of winter wheat, thus reducing N loss. In a recent study published in Frontiers in Plant Science, Haizhong Wu and colleagues investigated how combining this delayed N application with soil synergists—specifically biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More and the nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate)—could further reduce N2​O emissions by modulating the soil’s microbial community.

The researchers conducted a field experiment on winter wheat over two seasons in the North China Plain, a major dryland agricultural region. They compared six treatments under a delayed N application regime, including a control with no N (CK), an optimal N rate (ON, 180 kg N ha−1), a conventional farmer rate (FN, 270 kg N ha−1), and treatments combining ON with biochar (ONB), DMPP (OND), or both (ONDB). The study’s results demonstrated that the delayed N application strategy itself can significantly mitigate N2​O emissions.

When comparing the treatments that used an optimal N rate (ON), the addition of DMPP showed a clear advantage. The cumulative N2​O emissions (CE-N2​O) were significantly reduced by 32% in the OND treatment compared to the ON treatment. The best performance, however, came from the ONDB treatment (optimal N plus biochar plus DMPP), which reduced CE-N2​O by 38% compared to the ON treatment. This dual-synergist strategy (ONDB) also proved more effective than DMPP alone (OND). Conversely, the FN treatment (farmer conventional N application) actually increased N2​O emissions by 38% over the ON treatment, while biochar alone (ONB) increased emissions by 4%. The emission factors for N2​O under the delayed N regime were also substantially lower (ranging from 0.23% to 0.56%) than those under the normal N application regime (ranging from 0.60% to 1.03%).

The study linked these emission changes directly to shifts in the soil microbial community, particularly the functional genes responsible for the N cycle: nitrification and denitrification. Nitrous oxide is a byproduct of both processes. DMPP’s role is to inhibit nitrification, which is primarily regulated by ammonia-oxidizing microorganisms (AOA and AOB). The study found that DMPP application (OND and ONDB treatments) significantly reduced the abundance of ammonia-oxidizing bacteria (AOB) gene copies, confirming its inhibitory function. DMPP also increased the relative proportion of the AOB genus Nitrospira. A key finding from the random forest analysis was that Nitrospira was the genus within the AOB community that most significantly influenced N2​O emission. This suggests that DMPP decreases N2​O emissions by reducing the abundance and diversity of AOB and increasing the relative proportion of Nitrospira.

Biochar’s role appears to be more complex. When applied alone (ONB), biochar significantly enhanced the soil nitrate ( NO3−​-N) content, suggesting it stimulated nitrification. It also enhanced the soil pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More and soil organic carbon (SOC) content, raising pH by up to 3% and SOC by 7% in the ONB treatment compared to ON. However, when combined with DMPP (ONDB), biochar’s main contribution shifted to pH modulation and a substantial decrease in the denitrification substrate (NO3−​-N). The ONDB treatment increased soil pH by 5% and SOC by 8% compared to ON. The pH increase is crucial, as a significant negative correlation was found between pH and CE-N2​O.

Overall, the ONDB treatment provides a dual advantage by reducing N2​O emissions and enhancing N use efficiency under the delayed N application regime. This synergistic effect is proposed to be due to DMPP’s inhibition of AOB combined with biochar’s beneficial modulation of soil pH and subsequent impact on the availability of denitrification substrate. This comprehensive strategy is a promising approach for regions that use high N inputs, though a cost-benefit analysis is needed for wider farmer adoption.

Source: Wu, H., Zhang, D., Shen, X., Ma, G., Yuan, Q., Zhao, H., Liu, S., Jie, X., & Wang, D. (2025). Combined biochar and DMPP reduce N2​O emissions in wheat crops via microbial community modulation. Frontiers in Plant Science, 16:1647453. doi:10.3389/fpls.2025.1647453