Abstract: Under the conditions of high yielding cotton-wheat double cropping system, the effect of the composite root population of wheat-cotton double cropping system on soil enzyme activity and soil nutrient content at cotton rhizosphere and non-rhizosphere zones was studied in 3 treatments, i.e. wheat-cotton double cropping system in which the roots of wheat and cotton mixed naturally (WCRM), wheat-cotton double cropping system in which the roots of wheat and cotton separated with nylon net (WCRN),and wheat-cotton double cropping system in which the roots of wheat and cotton separated with plastic film(WCRP). The results showed that: in the symbiotic period of wheat and cotton, compared with WCRP, the activity of urease, invertase and protease at cotton rhizosphere and non-rhizosphere soil increased in WCRM and WCRN, and the soil enzyme activity in WCRN was the highest one. The soil nutrient content at cotton rhizosphere and non-rhizosphere zones reduced in WCRM, and the soil nutrient content in WCRN was the highest one as a result of yarn net slowed down the nutrient competition of wheat root to cotton root and secretion from wheat root's enhancement at the same time. In full-bud stage, wheat had been harvested, the soil enzyme activity and soil nutrient content at cotton rhizosphere and non-rhizosphere zones improved in different degrees in the composite root population, and WCRM improved the most, it's urease and invertase activity was the highest, and the soil organic matter content and total nitrogen content were higher than WCRP, but lower than WCRN. In wheat-cotton double cropping system, there were not only disadvantage nutrition competition between wheat and cotton at underground part, but also advantage part in which the soil enzyme activity and soil nutrient content at cotton rhizosphere and non-rhizosphere zones improved.

Key words: Cotton, Wheat-cotton double cropping, Roots, Soil enzyme, Soil nutrient