Optimizing phosphate fertilizer application to reduce nutrient loss in a mustard (Brassica juncea var. tumida)-maize (Zea mays L.) rotation system in Three Gorges Reservoir area

Soil nutrient loss is considered to be one of the most important causes of agricultural ecosystem degradation, but a scarcity of comprehensive research has evaluated nutrient losses affected by the reduction in application of specific fertilizers. Here, five phosphate fertilization treatments with conventional phosphate fertilization of 300 kg P2O5 ha(-1) yr(-1), 3/4 conventional phosphate fertilization, 1/2 conventional phosphate fertilization, 1/4 conventional phosphate fertilization and zero phosphate fertilization were conducted in a mustard-maize rotation system of the Three Gorges Reservoir (TGR) area. The contents of nitrogen (N), phosphorus (P) and potassium (K) in surface runoff and subsurface leachate and nitrous oxide (N2O) emission were compared among treatments. Results indicated that reduction of phosphate fertilizer rates from that the current typical rates significantly affected soil nutrient loss in the mustard-maize rotation system in the TGR area, and the effect on surface nutrient loss and N2O emission were the most significant. The 3/4 and 1/2 conventional phosphate fertilization treatments have no effect on nutrient uptake in mustard and maize, but decreased soil nutrient loss. A Gaussian model fit of data showed that the application of 150-250 kg P2O5 ha(-1) yr(-1) was most conducive in improving plant nutrient utilization. Therefore, reducing the phosphate fertilizer application by one-quarter to half of the amount used by conventional fertilization standards in the TGR area is beneficial to decrease soil nutrient loss and restore the ecological degradation of the mustard-maize rotation system.