Abstract: Rice production is heavily relied on the application of mineral fertilizers in Northeast China. Using a field experiment, we investigated the effects of mineral nitrogen fertilizer partially substituted by organic manure on soil enzyme activities and ecological indices of enzyme community, with the aim to provide scientific basis for reducing the application of mineral nitrogen fertilizer. We compared the activities of seven soil enzymes involved in carbon (C), nitrogen (N), and phosphorus (P) transformations under conventional fertilization (CF) and organic manure substitution (MS) treatments, the activities of which were measured by microporous plate fluorescence method. Our results showed that, compared to CF, MS significantly increased the contents of soil organic carbon (SOC), available phosphorus (AP), aggregate stability, and C∶N ratio, and increased the activities of enzymes related to the transformation of soil C (e.g. alpha-glucosidase (AG), betaglucosidase (BG), cellobiase (CBH), and xylosidase (XYL)) and N (e.g. acetylglucosidase (NAG)). The BG/(NAG+LAP) was reduced by MS relative to CF, indicating a relative limitation of soil N availability in MS. The NAG/LAP was elevated by MS, implying that soil microbial community shifted towards fungal dominance in MS. There was no significant difference in enzymatic evenness index between MS and CF, suggesting the limitations of using the evenness index of enzyme community to indicate microbial diversity. Our findings demonstrate that the organic manure substitution can maintain high rice yield, improve soil physicochemical properties, and increase soil enzyme activity in Northeast China. The manure substitution should be encouraged as an effective option to reduce mineral nitrogen fertilizer application and improve soil fertility.

Key words: soil enzyme activity, enzyme community ecological index, organic manure, nitrogen fertilizer application reduction, soil fertility improvement.