Effects of different fertilization modes on rice yield and nitrogen loss in paddy soils under double cropping rice

To ensure food security, there has been an extravagant use of nitrogen (N) fertilizer in paddy fields. Both the increase in N fertilizer efficiency and reduce in N loss in paddy soils are important in agricultural management and environmental protection. Here, we investigated the effects of side bar fertilization on paddy yields, N use efficiency and N loss in paddy soils and to provide reference for improvement of rice N utilization. Six fertilization treatments were used in the study-control (T1), common fertilizers with conventional fertilization method (T2, N 280 kg·hm^-2, P₂O₅ 165 kg·hm^-2, K₂O 120 kg·hm^-2), slow-release fertilizer with conventional fertilization method (T3, N 230 kg·hm^-2, P₂O₅ 165 kg·hm^-2, K₂O 120 kg·hm^-2), high slow-release fertilizer plus side bar application (T4, 230 kg·hm^-2, P₂O₅ 138 kg·hm^-2, K₂O 120 kg·hm^-2), medium slow-release fertilizer plus side bar application (T5, N 180 kg·hm^-2, P₂O₅ 123 kg·hm^-2, K₂O 120 kg·hm^-2) and low slow-release fertilizer plus side bar application (T6, N 140 kg·hm^-2, P₂O₅ 123 kg·hm^-2, K₂O 120 kg·hm^-2). The study was done in one cropping calendar at the Agricultural Environmental Sciences Observation Station in Yueyang City, Hunan Province, China. The results showed that combined application of slow release N fertilizer and side bar application method increased rice yield, promoted N utilization rate and reduced N loss in paddy fields. Particularly for T4, yields of both early and late rice increased respectively by 13.17% and 4.72%, and decreased rice planting density and applied N amount, compared with T2. The yields of both early and late rice under T4 treatment were 7.27% and 1.74% higher, respectively, than that of T3 treatment. Side bar fertilization significantly reduced N loss by 0.466-0.673 kg(N)·hm^-2 due to surface runoff decreasing by 3.54%-29.36%, compared with T2 treatment. Side bar fertilization significantly increased N use efficiency. N use efficiency under T4 treatment was 1.70 and 1.22 times that of T2 and T3 treatments, respectively. High slow-release fertilizer plus side bar application was the best fertilization mode in the study area. Our results were beneficial for improving productivity efficiency in agricultural, resources and environmental protection.