Effects of organic and inorganic fertilizer integration on soil chemical properties and rice yield/benefits in southern rice-rapeseed system

To investigate the effects of combined applications of lime, green manure, straw, and organic fertilizer on mitigating soil acidification and enhancing rice yield and economic benefits under a rapeseed–rice rotation system, a three-year field experiment was conducted. The experimental treatments included conventional fertilization with lime (L), green manure (G), organic fertilizer (M), straw (S), and a combination of lime, green manure, organic fertilizer, and straw (L+G+M+S), with conventional fertilization alone serving as the control (CK). From 2021 to 2023, changes in soil pH, organic matter content, total nitrogen, available phosphorus, available potassium, slow-release potassium, total cadmium content, rice yield, and economic returns were systematically monitored and analyzed, and the correlations among these parameters were further examined. Results indicated that all improvement measures (L, G, M, and L+G+M+S) increased soil pH compared to CK. However, only the L+G+M+S treatment showed a statistically significant increase, with an average rise of 0.44 pH units. Soil organic matter increased under all treatments, but significant improvements were observed only in the G, M, and L+G+M+S treatments, which increased by 9.19%, 11.4%, and 10.0%, respectively. Total nitrogen content increased under L, G, and L+G+M+S treatments by 11.2%, 12.4%, and 7.69%, respectively. Available phosphorus also increased across L, G, M, and L+G+M+S treatments, with only the M treatment showing a significant increase of 11.5% compared to CK. Soil slow-release potassium increased under G, M, S, and L+G+M+S treatments, with significant increases observed in G, M, and S treatments, rising by 10.7%, 6.05%, and 9.51% respectively. The L+G+M+S treatment also reduced soil cadmium content, with an average decrease of 0.02 mg·kg⁻¹. Among all treatments, the comprehensive improvement measure (L+G+M+S) effectively enhances the chemical properties of acidified soils, and demonstrates the most pronounced effects on increasing rice yield and net income, with a yield increase of 18.2% and an income rise of 1 776 yuan·hm⁻².