Effects of different rotation patterns on nitrogen and phosphorus loss in paddy fields under an optimal ratio of cow manure and fertilizer

In this study, based on a field plot experiment, we aimed to investigate the effects of different crop rotation methods on the loss of nitrogen and phosphorus in paddy fields under an optimal ratio of cow manure and fertilizer. To examine the changes in rice yield and total nitrogen(TN) and total phosphorus(TP) concentrations in paddy field surface water, infiltrated water, and runoff under different rotation patterns, we applied the following three rotation treatments:Y-OL(70% chemical fertilizer+30% cow manure-Lolium multiflorum Lamk.-rice); Y-OV(70% chemical fertilizer+30% cow manure-Vicia villosa Roth-rice); and Y-ON(70% chemical fertilizer+30% cow manure-winter fallow-rice). A conventional fertilization and tillage mode(C-ON:100% chemical fertilizer-winter fallow-rice) was used as a control treatment. The results reveled that the TN concentration in the surface water in different treatments peaked on the 2nd day after applying spiked fertilizer, the TP concentration peaked on the 2nd day of applying the basal fertilizer, and the highest values were obtained using the Y-ON treatment. In the C-ON and Y-ON treatments, the TN concentrations in infiltrated water peaked on the 2nd day of applying the basal fertilizer, whereas TN concentrations in the Y-OL and Y-OV treatments showed a peak on the 2nd day after applying panicle fertilizer. The overall TP concentration in infiltrated water during the entire rice growth period under Y-OV treatment was lower than other treatments. There were no significant differences in the amounts of nitrogen and phosphorus runoff loss between paddy fields. The amounts of nitrogen and phosphorus runoff loss in paddy fields were significantly correlated with rainfall, with TN runoff loss in each treatment accounting for 70.24%~73.42% of the total runoff loss, and TP runoff loss accounted for 35.12%~42.42% of the total runoff loss. Compared with the C-ON treatment, TN total loss in the Y-OV, Y-OL, and Y-ON treatments decreased by 43.92%, 25.21%, and 35.74%, respectively, whereas compared with C-ON, TP loss in the Y-OL and Y-ON treatments increased by 66.67% and 13.13%, respectively. However, TP total loss in the Y-OV treatment showed no significant difference from that in C-ON. Furthermore, we detected no significant differences in the rice yields obtained in the Y-OV, Y-OL, and Y-ON treatments and that obtained in the C-ON treatment. In summary, application of 70% chemical fertilizer + 30% cow dung fertilization in the Vicia villosa Roth-rice rotation system can ensure a high rice yield, effectively reduce the amounts of nitrogen loss in infiltration water and runoff, and maintain a low level of phosphorus loss, and can thus be considered an effective planting model for reducing non-point source nitrogen and phosphorus pollution and enhancing land-use efficiency.