| Research on effects of different amount of straw returning treatments on soil water,physical and chemical properties, crop productivity and WUE was conducted in semi-arid areas of southern Ningxia from 2007 to 2010. The results had a great theoretical and practical significance for improving the system of straw returning cultivation techniques; expand soil water storage capacity and providing a scientific basis for crop and soil fertilizing system in semi-arid regions. The main conclusions are as follows:1. The results of four years field experiment show that the application of straw returning can significant increase soil water storage. In the fourth experiment year (2010), follow the amount of straw returning from high to low, compared with CK, soil water storages(depth 0～200 cm) increased 4.56%, 3.01%, 2.52% and 6.44%, 4.42%, 2.28% respectively at the sowing and heading stage, soil water storages in high straw returning treatment is significant higher than CK(P<0.05); soil water storages(depth 0～200 cm) increased 6.26%, 5.04%, 3.77% and 9.44%, 7.05%, 5.30% respectively at the filling and maturity stage; soil water storages in high and middle straw returning treatment is significant higher than CK(P<0.05). In 0~200 cm soil layer, follow the amount of straw returning from high to low, compared with CK, the soil water storage is increased 22.25 mm, 17.97 mm and 12.65 mm respectively at the whole growth period of millet, straw returning treatment is significant higher than CK(P<0.05).2. The application of straw returning can increase nutrient obviously: In 0~20 cm soil layer, follow the amount of straw returning from high to low, compared with CK, soil organic carbon increased 24.16%, 20.78% and 9.50% (P<0.05) respectively; total nitrogen increased 38.89%, 25.93% and 18.52% (P<0.05) respectively; total phosphorus increased 11.11%, 9.26% and 5.56% (P<0.05) respectively; total potassium increased 3.60%, 2.97% and 2.66% respectively; available nitrogen increased 70.16%, 52.63% and 39.67% (P<0.05) respectively; available phosphorus increased 25.09%, 21.40% and 16.49% (P<0.05) respectively; available potassium increased 26.65%, 23.34% and 17.36% (P<0.05) respectively. Effects on soil nutrient under different straw returning treatments decreased with deeper layer.3. Three different levels of soil labile organic carbon decreased with deeper layer in soil; effects of straw returning treatment getting better and better with the prolonged time of treatment. In 0~20 cm soil layer, follow the amount of straw returning from high to low, compared with CK, labile organic carbon increased 29.30%, 40.76%, 30.57% (P<0.05) and 50.48, 46.62%, 35.05% (P<0.05) respectively; highly labile organic carbon increased 57.89%, 47.37%, 21.05% and 76.19%, 61.90%, 33.33% (P<0.05) respectively; middle labile organic carbon increased 41.67%, 43.75%, 27.08% (P<0.05) and 51.92%, 48.08%, 32.69% (P<0.05) respectively; CMI increased 35.61%, 45.45%, 35.45% (P<0.05) and 57.40%, 53.43%, 41.96% (P<0.05) respectively. Both 20~40 cm and 40~60 cm soil layer, showed the same trend.4. Obviously changes in rates and cumulative mineralization of organic carbon as affected by different straw returning treatments. The mineralization rates and accumulative mineralization increased with more straw returning and this affect in every straw returning treatment is significant higher than that of CK. On the seventh day of the incubation, mineralization rates of organic carbon have obviously difference between all treatments. In 0~60 cm soil layer, follow the amount of straw returning from high to low, compared with CK, daily average mineralization content increased 46.79%, 39.45% and 33.77%(P<0.05) respectively. With the incubation time prolonged, there was no significant difference between all treatments in soil CO2 production rate. After 49d of the incubation, CO2 cumulative emissions between 516.85～1968.06 g/kg and decreased with deeper layer, all treatments have no significant difference.5. The application of straw returning can affect soil enzyme activity obviously: In 2010 the soil layer of 0~60 cm, follow the amount of straw returning from high to low, compared with CK, soil catalase activity increased 4.82%, 3.22% and 2.63% respectively, high and middle straw returning treatment is significant higher than CK (P<0.05); soil urease activity increased38.68%, 34.89% and 22.95% (P<0.05) respectively; soil alkaline phosphatase activity increased 99.05%, 71.41% and 48.58% (P<0.05) respectively; soil invertase activity increased 90.12%, 80.94% and 53.45% (P<0.05) respectively. Additionally, the research also showed that, soil enzyme activity has enrichment effect on soil surface.6. The research showed that straw returning can decrease soil bulk density and increase soil porosity after four years experiment. In 0~60 cm soil layer, follow the amount of straw returning from high to low, compared with foundation soil, soil bulk density decreased 3.37%, 3.13% and 1.21% respectively, soil porosity increased 2.93%, 2.60% and 0.86% respectively, CK changed little. We also find that in 0~20 cm soil layer, straw returning can significantly increase the content of >0.25 mm soil mechanical aggregates and soil water-stable aggregates, enhance the stability of soil aggregates.7. Four-year experiment period, the straw returning treatment more stable on crop yields, and always higher than that of CK. Follow the amount of straw returning from high to low, compared with CK, in 2009 grain yield of corn increased 30.72%, 29.18% and 12.51% (P<0.05) respectively, the water use efficiency increased 41.10%, 35.89% and 21.28% (P<0.01) respectively; in 2010 grain yield of millet increased 27.45%, 23.18% and 11.53% (P<0.05) respectively, the water use efficiency increased 35.79%, 29.53% and 15.57% (P<0.05) respectively.Integrated the results of these four years, experiment, in the short term middle straw returning treatment can increase crop yield significantly, but in the long period, high straw returning treatment is superior. |
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