Effects of Organic Fertilizer Combined with Chemical Fertilizer on Nutrients, Enzyme Activities, and Rice Yield in Reclaimed Soil

A field experiment was conducted to explore the effects of combined application of organic and chemical fertilizers (organic-chemical fertilizers) on reclaimed soil fertility and rice yield. The experiment involved five treatments: no nitrogen (N) fertilizer (CK1), 100% chemical fertilizer N (CK2), 40% chicken manure N + 60% chemical fertilizer N (T1), 40% vermicompost N + 60% chemical fertilizer N (T2), 40% rapeseed meal fertilizer N + 60% chemical fertilizer N (T3). Organic-chemical fertilizers maintained or increased rice yield. Rice yields of T2 and T3 increased by 6.7% and 8.9%, respectively, as compared with CK2. T1 showed similar value of rice yield with CK2. Organic-chemical fertilizers application increased contents of soil organic C (SOC), total N (TN), alkali-hydrolyzable N (AN), NH4+-N, NO3–N, available phosphorus (AP), available potassium (AK) as well as CEC by 10.5%~15.9%, 8.9%~39.3%, 16.9%~74.5%, 38.1%~77.2%, 18.3%~136.5%, 27.7%~75.0%, 16.1%~24.7% and 7.2 ~ 26.0%. T3 had highest soil TN, AN, NH4+-N, NO3–N, CEC as well as T2 showed the highest contents of soil AP and AK. Organic-chemical fertilizers application increased soil sucrase (S-SC), urease (S-UE) and catalase (S-CAT) activities. The highest soil S-SC activity was detected in T3, and the highest soil S-UE and soil alkaline phosphatase (S-AKP) activities were observed in T2. Rice yield was positively related to SOC, TN, AN, NH4+-N, NO3–N, AP and AK as well as S-SC, S-UE and S-AKP activities. In conclusion, 40% organic N + 60% chemical N application could improve soil fertility and rice yield in reclaimed soils, with rapeseed meal fertilizer the most effective organic N source, followed by vermicompost and chicken manure.