Effects of irrigation with piggery wastewater on nitrate nitrogen dynamics in fluvio-aquatic soil

Effluent of three stages in piggery wastewater disposal process (raw water, effluent of anaerobic tank, effluent of ecological pond and groundwater) which was mixed with groundwater of 1:5 scale (volume ratio) and three irrigation amounts of effluent of anaerobic tank were applied to irrigate winter wheat. Through monitoring the nitrate nitrogen content dynamics and residual, a better type of water source and suitable irrigation amount were found in order to provide theoretical bases for formulating a scientific pattern of irrigation with piggery wastewater. The results showed that soil NO-3-N content of a depth of 0～100 cm soil profile decreased first, and then increased, and decreased finally with the increase of soil layer depth under three different treatments of mixed water. The concentrations of NO-3-N in each soil layer after wheat harvest were higher than original NO-3-N content. The content of accumulated NO-3-N was significantly increased more after harvest than in jointing stage by irrigation with three different treatments of mixed water in a depth of 0～100 cm soil profile. And the variation of the content of accumulated NO-3-N was the smallest in the treatment of eco-pond/groundwater (1:5), so this water was suitable for irrigation. There was a positive correlation between irrigation with different amounts of anaerobic water and the leaching of NO-3-N and NO-3-N residual content, and the better was 500 m3/hm2 in this situation. The irrigation in grain filling stage may greatly increase the NO-3-N content in soil profile, so it is suitable for irrigation with groundwater in this period.