Abstract:

【Objective】 The purpose of this study was to investigate the effects of wheat-residue application on soil physical and chemical properties and enzymatic activities in soil as well as their relations. 【Method】 A mid-season japonica rice cultivar Yangjing 9538 was grown in field. Three treatments of N-fertilizer application, farmers’ N-fertilizer practice (FFP), SSNM based on chlorophyll measurement (SPAD) readings, and no nitrogen application, and with or without wheat residue application (the straw was incorporated into soil) were conducted. Organic acid content, pH value, respiration rate, and enzymatic activity in soil were determined. 【Results】 The peak value of decomposition of wheat-residue was observed during the first month after rice transplanting. The contents of organic acids were increased significantly at mid-tillering and panicle initiation stages. Activities of urase and hydrogen peroxidase were enhanced initially and then decreased, and showed a peak value at 30 and 60 days after transplanting, and varied with development and growth stages. The activity of alkaline phosphatase in soil showed two peaks. The value of pH declined significantly, while the contents of organic acids were increased, under wheat-residue incorporation, and there was a negative correlation between them. The straw application increased the activities of urase, hydrogen peroxidase and alkaline phosphatase, organic matter content and respiration rate, while reduced ion contents of Na+, Mg2+ and Ca2+ in soil. Increase and decrease of the enzymatic activities and ion contents were associated with the decay degree of wheat-residue. Urase activity was higher under FFP than SSNM. There was no significant difference in other measurements of soil between FFP and SSNM. Activities of urase and alkaline phosphatase were significantly correlated with organic matter content and contents of total N, P and K. Hydrogen peroxidase activity was significantly correlated with the total N content, but not significantly correlated with the contents of total P and K in soil. 【Conclusion】 The results suggest that wheat-residue application could improve soil fertility through increase of organic matter content, enhancement of activities of enzymes, and reduction of contents of Na+, Mg2+, and Ca2+ in soil.

Key words: rice, wheat residue incorporation, soil, enzymatic activities, respiration rate, ion, organic matter