Effects of long-term cotton straw return and application of manure on soil nutrients and enzyme activity in cotton fields

Incorporation of straw and manure into soil plays an important role in nutrient management, maintenance of crop productivity, and improvement of soil quality. An experiment was conducted to clarify the effects of long-term cotton straw returning and manure application on soil nutrient and enzyme activities in continuous cropping cotton fields, and to provide scientific evidence for cotton straw returning and manure application. The experiment relied on a long-term experiment (since 2007) in an agricultural system conducted by the Niujiawa Cotton Agroecosystem Experimental Station of the Cotton Research Institute, Shanxi Academy of Agricultural Sciences. Four treatments were established on the base of application of nitrogen and phosphorus fertilizers, namely straw stubble removal (NP), straw returning (NPS), manure application (NPM), and straw returning + manure application (NPSM). The cotton yields of the treatments of NPS, NPM, and NPSM significantly increased by 10.23%, 11.10%, and 26.22% (P<0.05), respectively, compared with that of the NP treatment. The contents of soil total nitrogen, total phosphorus, alkali hydrolyzable nitrogen, available potassium, and available phosphorus in the NPSM treatment significantly increased by 48.76%–60.18%, 91.23%–112.18%, 140.63%–229.17%, 35.86%–60.54%, and 146.92%–483.34% (P<0.05), compared with those of the NP treatment, respectively. NPSM treatment significantly increased soil enzymes activities (P<0.05): urease activity by 118.50%–151.84%, phosphatase activity by 76.81%–93.11%, catalase activity by 30.53%–41.33%, and invertase activity by 83.41%–129.32%, compared with those of the NP treatment. There were significant positive correlations between soil nutrient content and soil enzyme activity. Therefore, long-term straw return with manure application can significantly increase cotton yield, nutrient content, and enzyme activity for soil fertility improvement in continuously cropped cotton fields.