Variation of nitrogen concentration in drainage water from paddy fields under controlled irrigation and drainage

Taking ditch-pond wetland system into account, with two treatments, namely controlled irrigation drainage and conventional shallow-wetting irrigation with no drainage regulation, nitrogen concentrations in drainage water from paddy fields were monitored and the variations of nitrogen concentrations were investigated. The results showed that comparing with conventional shallow-wetting irrigation during the whole growth period of rice, total nitrogen (TN), NO3--N, NH4+-N concentrations under controlled irrigation were reduced by 12.08%, 20.33% and 13.51%, respectively; comparing with conventional drainage, TN, NH4+-N and NO3--N concentrations under controlled drainage was reduced by 2.21%, 7.08% and 20.92%, respectively. TN, NH4+-N and NO3--N concentrations from inlet to outlet of the wetland were lowered by 16.8%, 14.4% and 50.9%, respectively. TN, NH4+-N, NO3--N concentrations in the wetland attenuated exponentially with time. Overall, the measures of controlled irrigation, controlled drainage and the ditch-pond wetland system are effective in removing nitrogen in drainage water from paddy fields.