Preliminary Research on Soil Nutrients and Bioactivity in Continuous Cropping Cotton Fields of Dryland in South Xinjiang

The nutrient status,enzyme activites and soil microbes were investigated in continuous cropping cotton field in south Xinjiang.The results showed that the total salinity,sodium and potassium salts and exchangeable potassium trended to decline in continuous cropping cotton fields.On contrast,soil nutrients,soil enzyme activates and soil microbes were observed to accumulate.No significant difference was found for available iron,available copper and available zinc in continuous cropping cotton fields.The activities of soil urease,alkaline phosphatase and invertase increased,but catalase activities declined.The majority of soil micro-organism was bacteria in continuous cropping cotton fields,actinomycetes and fungi occupied minor proportion.Numbers of bacteria,actinomycetes,fungi,azotobacteria and phosphate bacteria increased in short-term and decreased in long-term continuous cotton cropping fields,but the number of potassium dissolving bacteria increased in linear manner.Soil invertase,urease and Alkaline phosphatase activities could be cited as a comprehensive index of soil fertility.Path analysis showed that organic matter content,available potassium were two important factors which affect soil micro-organism composition and soil enzyme activities greatly.