| A field experiment has been conducted to explore straw decaying regulation and its mechanism of improving soil fertility under winter wheat-summer maize cropping system in Huanghuai area with wheat cultivar of Xinong 979 and summer maize cultivar of Zhengdan 958 from October 2013 to September 2014. Four treatments have been applied namelyfully straw returned with application of conventional fertilization(300 kg·hm-2 pure nitrogen)(SF), straw returned with application of conventional fertilization(300 kg·hm-2 pure nitrogen) and straw-decomposing inoculant(SFD), fully straw returned with application of conventional fertilization(300 kg·hm-2 pure nitrogen) and organic fertilizer(SFM), straw returned without fertilizer as control(CK). By analyzing the effect of straw decomposition promoting measurements on soil physical, chemical and biological traits, crop growth and development, yield formation and straw decomposition characteristics, we try to obtain an optimal straw decomposition promoting measurement in field condition. The main results were listed as below:1. Under winter wheat and summer maize cropping system, straw returning with application organic fertilizer(SFM) and with the application of straw decomposition agent(SFD) can significantly improve topsoil moisture content and nutrient content, improve soil structure, increase soil microbial activity. SFD and SFM treatments can significantly improve > 0.25 mm water stable aggregates proportion and reduce the < 0.25 mm water stable microaggregates proportion in 0-20 cm soil layer. The proportion of water stable aggregates of 0-20 cm soil layer was higher in the summer maize season than in winter wheat season. SFD and SFM treatments also can improve soil moisture, increase the soil alkali hydrolyzable nitrogen, available phosphorus and available potassium content, enhance soil urease, invertase, alkaline phosphatase activity at the winter wheat and summer maize growth period.2. Under winter wheat and summer maize cropping system, straw returning with application organic fertilizer(SFM) and with the application of straw decomposition agent(SFD) can increase crop photosynthesis and grain yield. The leaf SPAD value and net photosynthetic rate(Pn) in blossom stage and filling stage were higher in SFD and SFM than in SF treatment. Straw decomposed more quickly in SFD, SFM and SF than in CK. SFM treatment had the highest aboveground biomass accumulation among all 4 treatments in winter wheat and summer maize growth season. The yield of wheat and maize was higher in SFM and SFD treatments than the others. The significant difference exsited among SFD, SFM and SF treatments in 2014.3. Under winter wheat and summer maize cropping system, straw decay promoting treatment can significantly reduce the annual nitrogen surplus, improve crop nitrogen utilization efficiency, reduce the rate of contribution of soil fertility on Yield and increasing economic benefits of arable land. In winter wheat and summer maize cropping system, SFD, SFM and SF treatments can significantly improve crop nitrogen harvest index, nitrogen physiological efficiency, nitrogen partial productivity and nitrogen input-output ratio. The effect was the best under SFM treatment, and the effect was slightly lower in SFD than in SFM treatment.CK was only straw returned to the field, which caused nitrogen deficiency in farmland ecosystem, while SFD, SFM and SF treatmens showed an nitrogen surplus under nitrogen fertilizer of 300kg·hm-2 based on nitrogen balance analysis. SFD and SFM treatment showed a comparatively lower nitrogen surplus than SF treatment. From the economic perspective, SFD and SFM had higher capital input than SF treatment, while the annual economic benefit and net income was higher than SF treatment for 37.99% and 9.47% respectively. After two consecutive years of experiment, the yield contribution of soil fertility was decreased under SFD, SFM and SF treatments, in which annual fertility contribution to yield in SFM, SFD treatments was reduced by 9.39% and 8.86% respectively, that was significantly higher than in SF treatment.4. The field straw decomposing experiment by nylon bag indicated that maize straw decomposing rate was higher than wheat straw, which were 57.69%-67.79% and 59.10%-67.43% respectively. The annual cumulative straw decomposition rate ranged from 58.37% to 67.07%, and it showed the order of SFM>SFD>SF>CK. The proposal model of non linear regression in maize straw and wheat straw decomposition rate was the best fitting by simple cubic equation with R2 0.984-0.985, R2 0.992-0.999, and straw decomposing treatment with application of straw-decomposition agent(SFD) and organic fertilizer(SFM) showed the shortest compeletly decay time. Maize and wheat straw released 57.51%-68.80% and 56.41%-65.81% nitrogen of its own content and it also showed higher release in SFD and SFM treatments. Thereby, straw decomposing treatment with application of straw-decomposition agent(SFD) and organic fertilizer(SFM) showed the best effect on straw decomposing and nutrient release. |
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