| The objective of this study was to determine the soil physical and chemical properties and enzymes activities of cotton field after different continuous cropping ages in Ugan-Kuqa River Delta Oasis. Results showed that: The soil bulk density, coarse sand and fine sand contents increased with the increase of continuous cropping ages, whereas porosity and the clay content decreased; With the
increase of continuous cropping ages, pH value, salt and potassium contents decreased, whereas the contents of organic matter and alkaline hydrolytic nitrogen increased significantly, as well as available phosphorus content was relatively stable or decreased slightly. These changes resulted in imbalance of nitrogen, phosphorus, andpotassium; With the increase of continuous cropping ages, the
activities of urease, catalase, invertase, protease, and phosphatase increased at first, and then decreased. The changes of soil physical and chemical properties and enzymes activities were significant after 15 years of continuous cropping, except for the activities of protease and phosphatase which changed significantly after 20 years. It is therefore suggested that the maximum year of continuous cotton cropping be 15 years for Ugan-Kuqa River Delta Oasis. |