Effects of Long-Term Continuous Cropping System of Cotton on Soil Physical-Chemical Properties and Activities of Soil Enzyme in Oasis in Xinjiang

【Objective】 The objective of the experiment is to study the effect of long-term cotton continuous cropping on soil physical-chemical and biological characters. 【Method】 Both cotton micro-experiment and conventional chemical methods were adopted to study the changes of soil physical-chemical properties and soil enzyme activities under long-term continuous cropping. 【Result】 Results showed that compared with 1 year cropping, both soil organic matter content and soil salt content were increased by 10.56%, 18.09%, 37.34%, 55.64% and 122%, 132%, 124%, 146%, respectively, under 5-20 years continuous cropping, while soil bulk density began to decline. With the time of continuous cropping increasing, the soil alkali-hydrolyzable N content was remarkably raised, but the soil available K content was decreased by 60.4%, 35.9% and 39.8% under 5-20 years continuous cropping, the soil available P content was enhanced in 5-year continuous cropping and then stable in 10, 15 and 20 years continuous cropping. The activities of urase, catalase, protease, invertase and phosphatase decreased in 5-10 years continuous cropping, while those enzyme activities increased in 15-20 years, the soil peroxidase activity increased with the continuous cropping year increasing. 【Conclusion】 In the oasis area of Xinjiang, under long-term continuous cropping, stalk returning can ameliorate soil physical characters, increase soil salt content, but soil N, P, K proportion was imbalanced. The enzyme activity of soil decreased in a short period of time (from 1 to 10 years), the obstacles of continuous cropping were more obvious.