| The research was carried out in experimental farm of Yangzhou University during the years2010-2011. This study investigated nutrient release characteristies of wheat straw and effect of entire wheat straw returning. This provides a theoretical basis to develop a supporting fertilization technique for the mechanical wheat straw returning under high-yield cropping and ecology of field. The main results are as follows:1. The decomposition characteristic of wheat straw. The peak value of decomposition of wheat straw was observed during the first month after straw application under different treatments. The decomposition rate of straw was faster in the first30days, the cumulative decomposition rates of wheat straw was31.74%-52.16%, and then slowed down until the end of the experiment, the cumulative decomposition rates of wheat straw was4.34%-11.28%at this stage. Increasing nitrogen fertilizer could promote the decomposition of straw. The decomposition rates were respectively increased by14.07%,17.18%(clay soil) and8.30%,11.40%(sandy soil) under the nitrogen level of225kg/hm2and300kg/hm2. The decomposition rates of clay soil treatment were higher than sandy soil treatment. Nutrient release of wheat straw was consistent with decomposition dynamics. As for the nutrient release rate, it could be arranged with respect to nutrient release rate in this sequence:K>P>C>N. After90days, C, N, P, K release rate of wheat straw were respectively42.83%-51.33%,40.51%-47.62%,53.59%-62.75%and91.97%-93.82%. Nitrogen fertilizer and clay soil could promote the nutrient release of straw. The proportion of between carbon and nitrogen declined after straws returned to the field.2. During the first month after rice replanting, the contents of DOC were increased significantly under straw returning treatment, the soil surface particularly. The contents of DOC of straw returning treatment were two times than straw removing treatment. But the value of Eh, pH were decreased significantly at this stage. There were highly significant or significant negative correlations between the contents of DOC and the value of Eh, pH. Correlation coefficients were respectively-0.999**,-0.826*. Increasing nitrogen fertilizer could reduce the contents of DOC, while could promote the value of Eh, pH. There were not significant differences between nitrogen fertilizer treatments. The contents of clay soil DOC were higher than sandy soil, and the value of Eh, pH were entirely lower. The contents of soil nitrogen and activities of urase and hydrogen peroxidase were entirely increased significantly after straw returning. Compare with straw removing treatment, the activities of urase and hydrogen peroxidase of straw returning treatment were respectively increased by10.12%,21.19%(clay soil) and9.76%,19.78%(sandy soil). Increasing nitrogen fertilizer could promote the contents of soil nitrogen and activities of urase and hydrogen peroxidase. The effects of applying with straw and nitrogen fertilizer on them were significant. The contents of clay soil nitrogen and activities of clay soil urase and hydrogen peroxidase were entirely higher than sandy soil. Jointing, heading and maturity, there were highly significant correlations between the activity of urase and the contents of soil nitrogen. Correlation coefficients were respectively0.922**,0.932**,0.899**; there were highly significant or significant correlations between the activity of hydrogen peroxidase and the contents of soil nitrogen. Correlation coefficients were respectively0.670*,0.695*,0.667*.3. In comparison with straw removing treatment, the number of stems and tillers were lower under straw returning treatment during the early growth period, while the straw returning increased the percentage of productive tiller. Biomass accumulation significantly increased under straw returning treatment during the late growth period.Biomass accumulation significantly of straw returning treatment was increased by11.79%(clay soil) and11.49%(sandy soil) during the late growth period. Increasing nitrogen fertilizer could promote the number of stems and tillers and biomass accumulation. In comparison with sandy soil treatment, the number of stems and tillers and biomass accumulation were higher under clay soil treatment.4. Accumulation of nitrogen to content of total nitrogen uptaking was31.74%(clay soil),31.28%(sandy soil) under straw removing treatment from jointing to heading; accumulation of nitrogen to content of total nitrogen uptaking was24.56%(clay soil),24.13%(sandy soil) under straw removing treatment from heading to maturity. Accumulation of nitrogen to content of total nitrogen uptaking was34.51%(clay soil),34.09%(sandy soil) under straw returning treatment from jointing to heading; accumulation of nitrogen to content of total nitrogen uptaking was26.23%(clay soil),26.10%(sandy soil) under straw returning treatment from heading to maturity. Increasing nitrogen fertilizer could promote the content of nitrogen. The effects of applying straw with nitrogen fertilizer on the content of nitrogen were significant. In comparison with sandy soil treatment, the contents of nitrogen were higher under clay soil treatment. In comparison with straw removing treatment, ANRE, ANUE, PNUE were respectively increased by4.25%-5.10%,4.46%-5.48%and0.19%-0.37%under straw returning treatment.5. In comparison with CK, yield of straw returning treatment were respectively increased by3.78%and3.15%under clay soil and sandy soil treatment. The effects of applying straw with nitrogen fertilizer on yield of rice were significant. Under the nitrogen level of225kg/hm2, yield of straw returning treatment were respectively increased by3.97%(clay soil) and3.29%(sandy soil). Under the nitrogen level of300kg/hm2, yield of straw returning treatment were respectively increased by4.11%(clay soil) and3.42%(sandy soil). There were significant differences between treatments. In comparison with sandy soil treatment, yield of rice were higher under clay soil treatment. The straw returning reduced panicles per area, and increased the spikelets per panicle, filled-grain percentages and1000-grain weight. |
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