Effects of different nitrogen fertilizer types on ammonia volatilization and nitrogen use efficiency of rice-oilseed rape rotation systems

The rice-oilseed rape rotation is one of the main rotational patterns in China. However, excessive nitrogen fertilizer application reduces nitrogen use efficiency and causes nitrogen loss during rotation. In this study, a field experiment with a randomized block design was conducted to investigate the effects of different nitrogen fertilizer types on ammonia volatilization and nitrogen use efficiency during rice-oilseed rape rotation. Five treatments were applied: urea (UF), slow-release fertilizer + urea (SF), urea + nitrification inhibitor + urease inhibitor (DF), biochar + urea (BF), and no nitrogen fertilizer (CK). The results showed that the nitrogen fertilizer type significantly affected NH₃ volatilization, nitrogen use efficiency, and grain yield. 1) Ammonia volatilization was higher during the rice season than during the oilseed rape season. Compared with the CK, the UF, SF, DF, and BF treatments significantly increased the annual NH₃ volatilization by 1.6, 1.0, 1.1, and 0.8 times, respectively. Moreover, compared with the UF, the SF, DF, and BF treatments significantly reduced the annual cumulative NH₃ volatilization by 20.5%, 19.7%, and 30.9%, respectively. 2) Compared with the UF, the SF, DF, and BF treatments increased the nitrogen recovery efficiency by 27.9%, 10.3%, and 19.3% in the oilseed rape season and by 49.3%, 32.8%, and 41.5% in the rice season, respectively. 3) Compared with the UF, the SF, DF, and BF treatments increased the oilseed rape yield by 6.7%, 2.8%, and 4.3%, and the rice yield by 36.7%, 14.0%, and 23.4%, respectively. Compared with the UF, the SF treatment significantly increased the economic benefit in the oilseed rape season by 24.3%, whereas the SF, DF, and BF treatments increased the economic benefit in the rice season by 70.7%, 21.1%, and 1.1%, respectively, with the highest economic benefit observed in the SF treatment. The results of this study show that slow-release fertilizer plus urea is an economic and ecological fertilization mode for reducing the NH₃ volatilization loss of rice-oilseed rape rotation and improving nitrogen recovery efficiency, yield, and economic benefits.