Effects of lateral depth and irrigation level on nitrate and Escherichia coli leaching in the North China Plain for subsurface drip irrigation applying sewage effluent

Abstract

Subsurface drip irrigation is a sound method to apply sewage effluent, but there is a risk of nitrate and pathogen leaching. Field experiments were conducted during the maize growing seasons of 2014 and 2015 in the North China Plain to investigate the effects of lateral depth, irrigation level, and water quality on the deep percolation and the nitrate (NO3–N) and Escherichia coli (E. coli) leaching under semi-humid conditions. The experiments were designed with three lateral depths of 0 cm (D1), 15 cm (D2), and 30 cm (D3) beneath the soil surface along with three irrigation levels of 70% (I1), 100% (I2), and 130% (I3) of crop evapotranspiration requirements. Secondary sewage effluent and groundwater were used as irrigation water. The results indicated that the intensive rainfall caused most of the deep percolation and NO3–N leaching during the maize growing seasons. A high irrigation level usually produced more deep percolation and NO3–N leaching, but no significant difference was found among the treatments. In general, the cumulative NO3–N leaching beyond the root zone increased as lateral depth increased. In addition, the lateral depth obviously influenced the distribution of E. coli in soil, and subsurface drip irrigation usually induced E. coli contamination deeper in the soil. With relatively high nitrate and E. coli concentration, sewage effluent irrigation significantly increased the risk of NO3–N leaching beyond the root zone in the 2014 season, but imposed an insignificant influence on the presence of E. coli in soil. Furthermore, no E. coli was detected in the leachate following an irrigation event with sewage effluent or a rainfall event during the both maize growing seasons. A dripline depth of 15 cm with deficit irrigation can be conductive to reducing NO3 leaching as well as avoiding sewage effluent contact contamination during the maize growing season in the semi-humid region of the North China Plain.