棉花连作对渭干河-库车河三角洲绿洲土壤理化性质的影响

以渭干河-库车河三角洲绿洲连作5、10、15、20 a和25 a的棉田土壤为研究对象，对棉田土壤的理化性质和酶活性进行分析。结果表明： 随着棉花连作年限的增长棉田土壤容重增大、孔隙度下降，粗砂和细沙含量增加，粘粒含 量下降，其变化连作15 a极为明显； 随着连作年限的增长盐分含量和pH值逐渐降低，有机质和碱解氮含量大幅度升高，速效磷比较稳定或略有减小，而钾的含量显著下降，致使氮、磷、钾比例失调，其增减变化连作15 a极为显著； 随着连作年限的增长脲酶、过氧化氢酶和转化酶的活性呈现先升后降的趋势，连作15 a都达到最高值，蛋白酶和磷酸酶活性也呈现先升后降的趋势，但其活性连作20 a达到最高值。 由研究结果可以得出研究区棉花连作年限不宜超过15 a，棉花连作年限超过15 a时，会导致土壤容重增大、孔隙度下降，土体紧实板结，结构性差，土壤养分含量失衡，酶活性降低，土壤质量下降等连作障碍，使得棉花产出和效益受到影响。

Effect of continuous cotton cropping on soil physical and chemical properties in Ugan-Kuqa River Delta Oasis

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.