Nitrogen, phosphorus and potassium cycling and sustainability of rice yield in a winter crop-double cropping rice rotation system

The study of nitrogen (N), phosphorus (P), and potassium (K) nutrient cycling and yield sustainability in agricultural ecosystems is fundamental for achieving optimal nutrient management and sustainable agricultural development. A long-term experiment of a winter crop-double cropping rice rotation system initiated in 2004 on a red paddy soil in Hunan Province, consisting of five treatments, including fallow-double cropping rice (CK), potato-double cropping rice, ryegrass-double cropping rice, milk vetch-double cropping rice, and rape-double cropping rice with three replicates of all the treatments. The sustainability and stability of double cropping rice yields were analyzed, and N, P, and K cycling and balance were calculated based on an Input-Output analysis method. The results indicated:1) the sustainable yield index (SYI) and yield stability (CV) of early rice in the ryegrass-double cropping rice rotation system were 0.81 and 0.09, respectively. Winter ryegrass in the paddy field promoted the stability and sustainability of early rice yield. The SYI and CV of late rice in the rape-double cropping rice rotation system were 0.82 and 0.07, respectively. Winter rape in the paddy field improved of yield stability and sustainability of late rice. 2) Long-term winter crop-double cropping rice rotation did not significantly affect rice yield and the N, P, and K contents of brown rice (P>0.05). 3) Under the current input level of N, P, K in the annual rotation of winter crop and double cropping rice, the ryegrass-double cropping rice rotation, milk vetch-double cropping rice rotation, rape-double cropping rice rotation, and potato-double cropping rice rotation systems had serious K deficiency; the K deficit was 375.70, 279.98, 363.71, and 93.74 kg(K)·hm^-2, respectively. Ryegrass-double cropping rice rotation, milk vetch-double cropping rice rotation, and rape-double cropping rice rotation systems had serious K deficiency in the winter crop planting season, the K deficit was 240.07, 89.57, and 140.08 kg(K)·hm^-2, respectively. However, the potato-double cropping rice rotation system had a K surplus of 255.21 kg(K)·hm^-2 in the potato planting season; simultaneously, both the ryegrass-double cropping rice rotation and milk vetch-double cropping rice rotation systems had a N deficit in the winter crop planting season of 59.47 and 89.17 kg(N)·hm^-2, respectively. Both the rape-double cropping rice rotation and potato-double cropping rice rotation systems had serious K deficiency in the late rice planting season of 45.93 and 124.33 kg(K)·hm^-2, respectively. Nutrient cycling of winter crop-double cropping rice rotation systems was a nutrient cycle driven by winter crops and external N, P, and K fertilizers. Based on the results, the winter crops should be scientifically managed, with the input of N, P, and K in the three seasons.