Effect of reducing fertilizer application on crop yield and nitrogen and phosphorus loss in runoff from embankment upland in Dongting Lake Region

A continuous 2-year maize/rape rotation experiment was conducted to study the effects of five fertilization treatments on crop yield, fertilizer use efficiency, runoff-driven N and P loss and soil N, P contents. The study also explored excess N and P in the embankment upland of Dongting Lake Region (DLR). The five treatments were conventional fertilization, 85% conventional N application, 70% conventional N application, 70% conventional N application of slow-controlled release N fertilizer plus 80% conventional P application, and 80% conventional P application. The conventional applications of N, P₂O₅ and K₂O for maize field were 400 kg·hm^-2, 90 kg·hm^-2 and 135 kg·hm^-2, respectively. Those for rape field were 180 kg·hm^-2, 65 kg·hm^-2 and 60 kg·hm^-2, respectively. The results suggested that compared with conventional fertilization, reduced fertilizer application had no obvious effect on maize and rape yield. 70% conventional N application of slow-controlled release N fertilization plus 80% conventional P fertilization significantly improved N and P fertilizer use efficiencies of maize and rape. N fertilizer use efficiencies of maize and rape during the 2-year cultivation period averagely increased by 7.96% and 4.89%, respectively. Also P fertilizer use efficiencies averagely increased by 2.02% and 2.56%, respectively. Reduced fertilizer application decreased N and P loss via runoff by about 3.54%~29.36% and 7.14%~35.71%, respectively. Compared with conventional fertilization, total soil N, P and nitrate nitrogen contents under reduced fertilizer application were insignificantly different. Reduced slow-controlled release fertilizer application had the best performance among all the treatments. The results provided useful references for reasonable fertilization, prevention/control of regional agricultural non-point source pollution and protection of the water environments of DLR.