Effects of Mineral Fertilization and Organic Amendments on Rice Grain Yield, Soil Quality and Economic Benefit in Newly Cultivated Land: A Study Case from Southeast China

Low soil fertility and low microbiological activity have been widely observed in certain newly cultivated lands. To develop effective agricultural management practices that can improve soil quality rapidly, a field experiment was conducted on paddy fields reclaimed from unused, low-slope, hilly wasteland in Quzhou City, Zhejiang Province, Southeast China. The six treatments that were applied included (1) control (CK), no crops were planted and no fertilizers were applied; (2) R, rice planted without fertilization; (3) RR, rice-ryegrass rotation without fertilizer application; (4) RRM, rice-ryegrass rotation with the application of mineral fertilizer; (5) RRMO, rice-ryegrass rotation with the application of mineral fertilizer and organic manure; and (6) RRMH, rice-ryegrass rotation with mineral fertilizer and humic acid application. The results showed that the application of fertilizer with ryegrass cropping improved the amounts of soil organic C (SOC) by 115-296% and particulate organic C (POC) by 162-256% (p < 0.05). Additionally, the RRMO treatment had the highest soil quality index value (0.81), which was significantly higher (p < 0.05) than that of the other treatments. The random forest model showed that N-related properties (including urease activity, total N, and particulate organic N), C-related properties (including SOC, POC, and cellulase activity), and available P could significantly (p < 0.05) explain the response of rice yield to different fertilization management strategies. Compared with CK, the cultivated land quality grades of RRMO and RRMH increased from Grade 9 to Grade 7. However, the RRMH obtained the highest net profit from farmland quota trading. Overall, RRMO and RRMH are suggested to rapidly improve soil productivity and maximize the economic benefit of newly cultivated land utilization, respectively.