Mechanical side-deep fertilization mitigates ammonia volatilization and nitrogen runoff and increases profitability in rice production independent of fertilizer type and split ratio

Abstract A combination of nitrogen (N) fertilizer side-deep placement and mechanical transplanting of rice seedling (MSDF) has been recommended as an effective alternative technique to conventional broadcasting of fertilizer. However, its comprehensive interactions with N-fertilizer type, split ratio, environmental impact, and profitability are unclear. A three-year field experiment was conducted using MSDF and three fertilizer types (NPK briquette, F1; NPK briquette with nitrification inhibitor, F2; and controlled-released N fertilizer, F3) with 200 kg N hm−2 at two split ratios (a one-time basal application (N200) and basal plus supplementary application at the rice tillering stage (N140 + 60)). Conventional fertilization (conventional fertilizer using NPK briquettes by broadcasting with 270 kg N hm−2 at three split ratios (CF1N270)) and a no-N-added treatment were established as two controls. Directly reducing the N-application rate by 26% (CF1N200) decreased grain production by 13.1%. However, MSDF management (MF1N200, MF2N200, MF3N200, MF1N160 + 40, MF2N160 + 40, MF3N160 + 40) maintained high yield, increased NUE by 24.8–40.9%, and decreased NH3 volatilization and total N concentration in runoff by 39.0–65.6% and 29.1–59.3%, respectively. Moreover, there was no difference with fertilizer type and split ratio design among these MSDF treatments. When using a lower N-application rate (200 kg N hm−2), compared with CF1N200, MSDF treatments increased NUE by 43.6% and net economic benefit by 74.9%, and decreased NH3 volatilization and total runoff N concentration by 35.2% and 78.4%, respectively. MSDF at a reduced N-application rate minimizes NH3 volatilization and N runoff and increases profitability, independent of fertilizer type and split ratio.