Experimental study of nitrogen leaching pattern in controlled pipe-drainage cotton field

In order to study nitrogen leaching patterns in cotton field under different drainage treatments, a field pipe controlled drainage experiment was conducted at Yajiao Drainage and Irrigation Experimental Station, Jingzhou City, Hubei Province, in 2008. Results showed that under controlled drainage, accumulation of nitrogen loss from surface drainage was larger than that from pipe drainage. Pipe drain outflow reduced by 61.3%–86.9% as the depth of the outlet declined. Nitrogen loss of pipe drainage was mainly influenced by drain outflow. Ammonia nitrogen loss reduced with rising of the drainage outlet depth. Due to increment of the nitrogen concentration, nitrate and total nitrogen loss of 30 cm treatment were larger than that of 50 cm and 80 cm treatments. Depth of drainage outlet was suggested to be between 30 cm and 50 cm, which could reduce both drain outflow and nitrogen loss.