Increases of N2O emissions due to enhanced nitrification in a sandy loam soil under long-term manure application.

15N tracing was carried out on sandy loam soil amended with (i) mineral nitrogen-phosphorus-potassium fertilizer (NPK) alone, (ii) half mineral N and half N from chicken manure (HFC), or (iii) half mineral N and half N from cattle manure (HCM), for 8 years. Cumulative N2O emissions during incubation were 30.2 µg N kg− 1 in the NPK treatment, which increased to 37.8 and 51.3 µg N kg− 1 in the HFC and HCM treatments, respectively. The majority of N2O emissions in all the treatments were attributed to nitrification (81.0% in the NPK treatment, 83.0% in the HFC treatment, and 85.1% in the HCM treatment). Compared with NPK, HCM treatment caused a significant increase in the gross rate of nitrification, while HFC treatment slightly enhanced the rate of dissimilatory NO3− reduction to NH4+. Additionally, HFC treatment achieved higher gross rates of organic N mineralization, and both HFC and HCM treatments had higher NH4+ mineralization-immobilization turnover (<italic>MI</italic><italic>A</italic><italic>T</italic>) rates than NPK treatment. The results suggest that application of cattle or chicken manure increased soil NH4+ availability. The gross rate of NO3− adsorption in the HCM treatment was greater than that in the NPK treatment, while the release of adsorbed NO3− in the HFC treatment was slower than that in the NPK treatment, indicating that application of cattle or chicken manure lowered the potential for NO3− leaching in soil. Overall, combining cattle or chicken manure with mineral fertilizer decreased NO3− availability but increased NH4+ availability, leading to higher N2O emissions through nitrification. Our results suggest that organic manures should be applied with nitrification inhibitors in sandy loam soil containing low organic carbon to increase soil fertility and mitigate N2O emissions. [ABSTRACT FROM AUTHOR]