Coated controlled-release urea improves soil NO ₃ ⁻ −N accumulation, rubber yield and economic profit in a <i>Hevea brasiliensis</i> plantation

Mitigating nitrogen (N) loss via slow-released N is critical for sustainable rubber (Hevea brasiliensis) plantations. This study aimed to elucidate effects of coated controlled-release urea (CCRU) and conventional urea ratios on variations in soil and leaf N and rubber production. Treatments with the same total N input included 0% (N0, 100% conventional urea), 40% (N0.4), 60% (N0.6) and 80% (N0.8) of CCRU and corresponding conventional urea. Averaged results for the two whole 6-month periods (April to September) in 2019 and 2020 showed significantly higher monthly soil NO3−-N concentrations between all four CCRU fertilizations as N0.6 = N0.8 > N0.4 > N0 at both 0−20 cm and 20−40 cm depths, rubber concentrations as N0.6 = N0.8 = N0.4 > N0, rubber yield, partial factor productivity of N fertilizer and economic profit for rubber production as N0.8 ≈ N0.6 > N0.4 = N0, while leaf N or rubber yield significantly positively correlated with soil NH4+-N, NO3−-N or inorganic N. The 60% CCRU + 40% conventional urea (N0.6) suited mostly for the Yunnan mountainous rubber plantation. Our results can provide a better N fertilization strategy to increase N use efficiency and corresponding economic profit while mitigating N pollution risk for a sustainable rubber plantation.