Potato-Based Cropping Systems Improve Soil Quality by Increasing the Content of Available Nutrients and Aggregate Structure

Crop rotation plays a critical role in enhancing cropping intensity and ensuring food security. To evaluate its long-term effects on soil quality, a fixed-site field experiment established in 2014 including four cropping systems—winter fallow–rice (Oryza sativa L.) (FR), potato (Solanum tuberosum L.) –maize (Zea mays L.) (PM), potato–rice (PR), and potato–rice → rapeseed (Brassica napus L.) –rice (RRPR)—was conducted. A minimum data set (MDS) was screened from 21 soil indicators via principal component analysis (PCA), and the soil quality index (SQI) was calculated by integrating membership functions and indicator weights to comprehensively evaluate the impact of different patterns on soil quality. Results showed that paddy–upland rotations (PR and RRPR) significantly improved soil physical properties, increasing soil moisture content, porosity, and macro-aggregate proportion by 2.27–10.17%, while reducing bulk density by 10.32–13.38%, compared to FR and PM. PR and RRPR rotations also increased total nitrogen (TN), available phosphorus (AP), and available potassium contents (AK) by 5.19–114.00% (p < 0.01). PM rotation notably enhanced available nutrients, with NH4+-N, AP, and AK rising by 3.65–243.50% (p < 0.05), compared to FR. The MDS-based SQI, comprising NH4+-N, AP, mean weight diameter, and soil porosity, showed a highly significant positive correlation with the total data set-based SQI (p < 0.0001). PM exhibited the highest and most stable SQI, exceeding other systems by 8.15–19.30%, while PR and RRPR increased SQI by 9.04–10.30%, compared to FR. In conclusion, potato-based cropping systems enhance soil quality by improving soil structure and increasing nutrient content and availability. The results of this study provide a theoretical basis for nutrient management and sustainable production in cropping systems.