Effect of Nitrogen Fertilizer Rates on Soil Available Nutrients and Soil Enzymatic Activity Variation Characteristics in Cotton Field

The effects of nitrogen fertilizer rates on soil available nutrients and soil enzymatic activity variation characteristics in cotton field were studied in this paper.The results showed that nitrogen fertilizer rates could improve soil available nutrients and enzyme content at topsoil(0~20 cm) layer.The soil available nutrients contents increased gradually from seedling to blooming stage,decreased dramatically at boll-forming stage,and then increased gradually at opening stage.The profile distribution of enzymatic activity of soil: nitrogen fertilizer mainly affected urease distribution in topsoil layer,and phosphatase in 20 to 40 cm layer.Through correlation analysis: maximum of alkaline nitrogen content appeared later a growth stage than urease activity,but in all the variations trend of soil alkaline nitrogen was similar with urease.In a growth stage,the contents of soil organic matter,nitrogen,phosphorus and potassium had significantly positive correlation with the urease activity.The significant or very significant correlation existed between available phosphorus and phosphatase,enzymatic activity and available potassium.Nitrogen-free treatment: urease and phosphatase activity at seedling stage was significantly higher than others stages.