Effect of controlled-release fertilizers on ammonia volatilization from upland soils in a maize-oil rapeseed rotation system of Sichuan

Exploring the ammonia emission reduction effect resulting from different ratios of urea to controlled-release fertilizer, aims to provide a theoretical basis for achieving ammonia emission reduction in farmland, increasing crop yields and enhancing the economic benefits of farmers. Field experiments were conducted in the typical maize-oilseed rape rotation system in Deyang City, Sichuan Province, from 2022 to 2024. Under the condition of equal nitrogen (N) application amount (180 kg N ha⁻¹), six treatments combining with different ratios of urea and controlled-release fertilizer were formed: a control without N addition treatment, 100% urea treatment, 70% urea + 30% controlled-release fertilizer, 50% urea + 50% controlled-release fertilizer, 30% urea + 70% controlled-release fertilizer, and 100% controlled-release fertilizer. Based on continuous monitoring the soil ammonia volatilization conducted by the closed-chamber intermittent ventilation method during the crop growth period, we compared the ammonia emission reduction effects of different combination ratios of urea and controlled-release fertilizer, as well as their impacts on yield, nitrogen use efficiency and economic benefits. The cumulative ammonia volatilization in the maize season ranged from 7.8 to 50.1 kg N ha⁻¹. Compared with the application of urea alone, the ammonia volatilization could be significantly reduced by 31.0% and the economic benefits were significantly increased by 19.7%, when the addition proportion of controlled-release fertilizer was 70%. When the addition proportion of controlled-release fertilizer was 100%, the cumulative ammonia volatilization could be significantly reduced by 47.5% while the yield could be increased by 13.4%, the nitrogen agronomic use efficiency could be significantly improved by 58.2%, and economic benefits was significantly enhanced by 24.8%. The cumulative ammonia volatilization in the oilseed rape season ranged from 4.9 to 59.0 kg N ha⁻¹. Compared with the application of urea alone, when the addition proportion of controlled-release fertilizer was 30%, the ammonia volatilization could be significantly reduced by 25.1% while the yield could be increased by 10.7%, the nitrogen agronomic use efficiency could be significantly improved by 32.6%, and economic benefits was significantly enhanced by 26.4%. When the addition proportion of controlled-release fertilizer was 70%, the cumulative ammonia volatilization could be significantly reduced by 22.0% while the yield could be increased by 9.9%, the nitrogen use efficiency could be significantly improved by 51.0%, and economic benefits were significantly enhanced by 19.6%. In summary, the single application of slow-controlled release fertilizer in maize season and the application of slow-controlled release fertilizer and urea in the ratio of 3∶7 in oilseed rape season are an economical and environmentally friendly fertilization mode, which can significantly reduce the ammonia volatilization, while simultaneously improving yield, nitrogen use efficiency, and economic benefits in the maize-oilseed rape rotation system.