Objective Organic substitution of chemical fertilizer is one of the most widely used methods to increase nitrogen use efficiency. Enzymes are the major driving force of nitrogen (N) transformation after N is inputted into the soil. Thus, studying the effects of organic substitution of chemical fertilizer on N transformation-related enzymes in the soil is meaningful for increasing N use efficiency.
Methods This study took National Long-term Location Monitoring Base on Black Soil Fertility and Fertilizer Efficiency as a research platform. The activities of soil urease, catalase, polyphenol oxidase, nitrate reductase and nitrite reductase were determined during the maize growth period. A total of 4 treatments were involved in this study: no fertilizer application (CK), only chemical application (NPK), straw partly replaced chemical fertilizer application (NPKS), organic manure partly replaced chemical application (NPKM).
Results NPKS and NPKM enhanced activities of soil urease, catalase, nitrate reductase and nitrite reductase during maize growth period. The specific trend was NPKM > NPKS > NPK > CK. In contrast with NPK treatment, NPKM and NPKS averagely increased activities of urease by 29 and 21.9%, catalase by 2.7% and 2.2%, nitrate reductase by 39.8% and 24.1%, nitrite reductase by 8.4% and 6.1%. NPKS and NPKM exhibited opposite effects on polyphenol oxidase in contrast with NPK. NPKS averagely increased polyphenol oxidase activity by 15.9%. While, NPKM decreased polyphenol oxidase activities by 9.3% during the maize growth period. The activities of soil urease, catalase, polyphenol oxidase and nitrate reductase all exhibited a trend of initially increasing and then decreasing during the maize growth period, while nitrite reductase activities were increased gradually.
Conclusion Organic substitution of chemical fertilizer enhanced the activities of N transformation related enzymes in soil.
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