| In recent years, the utilization of crop straw has been becoming lower as the changes of fuel structure in rural areas.The residue burning of crop in field is a serious problem to the environment in modern time. However, it’s an effective way to return the crop stalks to field. That will not only reduce the environment pollution, but also can improve siol fertility condition and physics structure, and promote crop growing. At last, the staw turnover will increase the yield of crop and revenue. But there are some technical problems during the crop stalks to field, such as the methods of crop returning to field, how to avoide the negative effects, etc. In this research, the decomposition law of different stalks at different depth in field had been discussed. At the same time, the impaction of straw mulching (S) and staw mulching+decomposition agent (SD) to soil and crop had been analyzed by field experiment in Purple Hilly Region. The main research conclution as following:1. Studying the decomposition law of wheat and soybean straw in Purple Hilly Region with Wheat-Maze-Bean crops rotation pattern by method of nylon net bag.(1) The decomposition process of wheat straw at different depthes presented following characteristics:the depths of straw returning to field are Ocm (mulching, DO),5cm (D5),15cm (D15), respectively. After36weeks, the decomposition ratio:D5(81.56%)>D15(80.19%)>D0(61%); the releasing ratio of carbon:D15(83.76%)>D5(81.14%)>D0(62.81%); the releasing ratio of nitrogen: D15(43.11%)>D5(40.61%)>D0(19.67%). The the decomposition ratio, the releasing ratio of carbon and the releasing ratio of nitrogen of buried treatments are significantly higher than mulching treatment. The C/N of wheat straw is relative high, and it continuesly kept high level during decomposition process (higher or nearly80). At the last phase of decomposition the C/N declined to about30, but there was no significant difference between different treatments during the research stage.(2) The decomposition process of sobyean straw at different depthes showed following characteristics:all of decomposition ratio, carbon releasing radio, nitrogen releasing raito were D15>D5>D0; after36weeks, the decomposition ratio was62.25%(D0),72.87%(D5) and76.49%(D15) respectively; the releasing ratio of carbon was63.14%(D0),73.19%(D5), and77.15%(D15); the releasing ratio of nitrogen was D15(47.08%)>D5(44.78%)>D0(39.10%). It revealed that the buried treatments (at5and15cm) were signigicantly higher than mulching treatment about the above three indexes. The decomposition rate of soybean straw was fast at the beginning period, especially by buried treatment. The C/N of soybean stalks kept about50, but droping to approximate20at the last phase of decomposition.(3) There were different and similar laws between wheat and soybean stalks. Firstly, the max decomposition rate of wheat and soybean straw both appeared in the first two weeks after returning to field. However, the C/N of soybean straw was obviously lower than wheat straw during their whole docompositon process, so they showed different docomposition rules. The wheat straw decomposed little part during the first16weeks and the decomposition rate kept high level during16to36weeks. But the soybean straw decomposed more than40percent during the first16weeks under buried treatments. The C/N of both stalks is above the ultimate range for microbes living, and it kept going up during the most part of decomposition process. Therefore, the N fertilizer should be applied aproperly, according to the groth satge of crops and the releasing of nutrition of stalks after returning to field. That methord will relief the competition of nitrogen between crops and microbes. So the crops can grow better and the decomposition of straw will be promoted at the same time.2. The infulltion of staw mulcing to soil environment and crop growing and yield in Purple Hilly Region with Wheat-Maze-Bean crops rotation pattern.(1)Straw mulching (S) can significantly increase the number of microorganisms in surface soil, including bacteria, fungi and actinomycetes, by mornitoring during wheat growing season. At0to10cm soil layer, the number of bacteria, fungi and actinomycetes increased by80.6%,137.1%and143.8%, respectively, compared to control group (CK); at10to20cm soil horizon increased by149.0%,34.5%and38.5%respectively. On the other hand the mumber of microbes at10to20cm soil horizon was significantly more than0to10cm soil horizon. Among the three main kinds of microbes, the relationship of number was that bacteria> actinomycetes> fungi.(2) Straw muchling also can obviously enhance the activity of catalase, invertase and urease in surface soil by mornitoring during wheat growing season. The activity of catalase, invertase and urease at0to10cm soil layer by staw mulching treatment increased by51.5%,81.8%and47.7%, respectively, compared to CK. At the same time, the activity of the above three kinds of soil maze was increased by34.2%,87.0%and37.8%at10to20cm soil horizon, respectively. There was no significant difference between different soil horizons.(3) Furthermore, straw mulching can significantly enhance the soil respiration. The soil respiration rate of CK was between0.4and1.9μmol·(m2·s)-1during wheat growing season and the mean value was1.09μmol·(m2·s)-1. On the other hand the soil respiration was between0.5and2.7μmol·(m2·s)-1and the mean value was1.58μ(m2·s)-1; and it was0.6to2.7μmol·(m2·s)-1for straw muching+decomposition agent (SD) with mean value of1.41μmol·(m2·s)-1. Comparing to CK, the soil respiration rate of S and SD increased by45.0%and29.4%, respectively.(4) At last, straw mulching would obviously improve the growth of wheat after Seedling stage. The yields of wheat also increased by23.7%(S) and27.6%(SD) compared to CK. |
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