Effects of triple-cropping patterns on rice yield and soil nutrients in the middle reaches of the Yangtze River

To promote the sustainable development of paddy-upland rotation systems in the middle reaches of the Yangtze River, a long-term fixed-field experiment was conducted from 2017 to 2022. The study was designed with five typical triple-cropping patterns: Chinese milk vetch-early rice-late rice (CRR), Chinese milk vetch-early rice-sweet potato || late soybean (CRI), oilseed rape-early rice-late rice (RRR), oilseed rape-early rice-sweet potato || late soybean (RRI), and potato-early rice-late rice (PRR). The yield of dry crops was converted into late rice season yield based on the seasonal crop price ratio for comparison, to investigate the effects of different cropping patterns on rice yield and soil nutrient availability. The results showed that based on the six-year average rice yields, the late rice yield under treatment CRI was significantly higher than that under RRR by 24.09% (P<0.05), and the total yields under CRI and RRI were significantly higher than those under other treatments by 14.21%–18.18% (P<0.05). Among all treatments, CRI effectively increased the effective panicle number, grain number per panicle, seed-setting rate and 1000-grain weight of rice, which was conducive to yield improvement. According to the six-year average soil nutrient contents, soil organic matter contents in the late rice season under CRI and RRI were significantly higher than that under PRR by 21.33% and 17.54% (P<0.05). In addition, CRI with Chinese milk vetch planted in winter performed well in increasing soil total nitrogen and hydrolyzable nitrogen contents, which were significantly higher than those under PRR by 12.57% and 38.58% (P<0.05). Correlation analysis between rice yield and soil nutrients indicated that rice yield was significantly correlated with available phosphorus and hydrolyzable nitrogen (P<0.05), and significantly negatively correlated with pH (P<0.05). Therefore, in the triple-cropping paddy field areas of the middle reaches of the Yangtze River, the planting patterns of CRI and RRI are conducive to improving rice yield and soil fertility, and are suitable for popularization and application in the middle reaches of the Yangtze River.