Biochar Mitigates N ₂ O and NH ₃

ABSTRACT

Biochar is a promising soil management strategy to reduce reactive nitrogen (N _r ) losses from agricultural soils, and replacing mineral fertilizers with organic amendments (OAs) can improve soil health and enhance nutrient recycling. We conducted a three‐year field experiment with maize ( Zea mays ) in Lower Austria to compare organic waste compost and digestates with mineral nitrogen–phosphorus–potassium (NPK) fertilization (175 kg N ha ⁻¹ , 39 kg P ha ⁻¹ , 187 kg K ha ⁻¹ ) and to evaluate the effects of biochar application on nitrous oxide (N ₂ O), ammonia (NH ₃ ) emissions, and crop yield. Compost and digestates were applied at higher total N rates (350 kg N ha ⁻¹ ). Biochar (approximately 7.5 t ha ⁻¹ ) was applied in combination with NPK or compost at the same fertilizer application rates as the respective non‐biochar treatments to assess its potential to mitigate gaseous N _r losses. Treatment effects on soil properties and microbial functional gene abundances were also evaluated. Overall, compost reduced cumulative N ₂ O and NH ₃ emissions by 66% and 68%, respectively, whereas digestate increased emissions by 21% (N ₂ O) and 32% (NH ₃ ) compared to NPK. Biochar‐amended soils mitigated N ₂ O emissions by 48% under NPK and 39% under compost. Moreover, NH ₃ volatilization was reduced by 51% for NPK and 26% for compost when biochar was added. In reference to yield, digestates successfully substituted NPK, whereas compost did not provide equivalent short‐term nutrient supply due to limited N‐mineralization rates. Soil organic carbon and total nitrogen (TN) increased under OAs, indicating long‐term fertility benefits. Reduced N ₂ O emissions under biochar amendment could be linked to a lower denitrification potential in these treatments, while the availability of nitrate () and ammonium () was not affected by biochar amendment, as confirmed by analysis of abundance of N cycling genes and soil extractions. Our research demonstrates that both OAs and biochar can serve as climate‐smart agriculture tools by improving soil fertility and supporting C sequestration while reducing direct N ₂ O and NH ₃ emissions. However, effective fertilization management is necessary to maintain high yields, requiring integrated nutrient management strategies that strategically combine OAs with mineral N fertilization.