Effects of nitrogen application rate and phosphorus fertilizer management on silage maize yield and nutrient utilization

【Objective】To investigate effects of different nitrogen application rates and phosphorus fertilizer managements on silage maize yield and nutrient uptake and utilization，and to provide a theoretical basis for ecofriendly and efficient silage maize cultivation technology.【Method】With silage maize Qiaodan 6 as the experimental material，field experiments were conducted from 2021 to 2022. Two treatments of nitrogen application，N1（20% nitrogen reduction， 240 kg/ha）and N2（conventional nitrogen application rate，300 kg/ha），were set. Under each nitrogen application rate，three phosphorus fertilizer managements were set：P1（100% basal fertilizer），P2（50% phosphorus fertilizer and 50% ear fertilizer），and P3（50% jointing fertilizer and 50% ear fertilizer），altogether 6 treatments. Dry matter accumulation， fresh grass yield，nutrient uptake and utilization，soil nutrient and enzyme activity of silage maize were determined under different nitrogen application rates and phosphorus managements.【Result】Nitrogen application rates influenced silage maize biomass，and the influence of N1 treatment was smaller than that of N2. Phosphorus fertilizer topdressing increased silage maize biological yield，under N1 nitrogen application rate，silage maize biological yield in P2 treatment was significantly higher than those in P3 and P1 treatments（P<0.05，the same as below）；under N2 nitrogen application rate，silage maize biological yield in P3 treatment was significantly higher than those in P2 and P1 treatments. In each combination of treatments，the fresh grass yield in N1P2 and N2P3 treatments were significantly higher than that in N2P1 treatment（conventional fertilization）. Nitrogen and phosphorus uptake in N2 treatment was higher than that in N1 treatment，while phosphorus fertilizer topdressing significantly increased nitrogen and phosphorus nutrient uptake and utilization. Under N1 nitrogen application rate，nitrogen and phosphorus uptake in milking stage was as P2>P3>P1 and under N2 nitrogen application rate，it was as P3>P2>P1. In each treatment，nitrogen and phosphorus uptake in N2P3 treatment at milking stage was significantly higher than that of N1P2 and N2P1 treatments. Compared to N2P1 treatment，nitrogen uptake in N1P2 treatment in 2021 and 2022 increased by 9.52% and 9.03%，and the phosphorus uptake increased by 4.69% and 9.45%. At silking stage and milking stage，phosphorus uptake and nitrogen uptake in maize were extremely significantly positively correlated（P<0.01）. In addition，reducing nitrogen by 20% generally decreased partial productivity of phosphorus fertilizer， but increased partial productivity of nitrogen fertilizer. Partial productivity of nitrogen fertilizer in N1P2 treatment in 2021 and 2022 was significantly increased by 36.91% and 39.62%，respectively. Partial productivity of phosphorus fertilizer in N2P3 treatment was significantly higher than that in N2P1 and N1P2 treatments；partial productivity of phosphorus fertilizer in N1P2 increased by 4.71% and 9.51% in 2021 and 2022，compared to that in N2P1 treatment. Nitrogen reduction of 20% usually reduced content of alkali-hydrolyzed nitrogen，available phosphorus，urease and acid phosphatase activity， while phosphorus fertilizer topdressing increased enzyme activity and soil available nutrients，and P2 and P3 treatments were higher than P1 treatment. Among treatments，N1P2 and N2P3 could maintain higher soil urease and acid phosphatase activity，promote accumulation of alkali-hydrolyzed nitrogen and available phosphorus，and increase plant dry matter accumulation，nitrogen and phosphorus uptake and utilization compared to N2P1.【Conclusion】Phosphorus fertilizer topdressing increases soil enzyme activity and soil available nutrients，promotes nutrient absorption and utilization of maize， thus lowering yield loss caused by nitrogen reduction. In terms of nitrogen application rate and phosphorus management methods，N1P2 and N2P3 treatments enhance efficient utilization of nitrogen and phosphorus nutrient resources and increase yield.