Influence of Lateral Length and Residual Chlorine Concentration on Soil Nitrogen and Soil Enzyme Activities under Drip Irrigation with Secondary Sewage Effluent

Chlorination has been demonstrated to be an effective method for the prevention and reduction in emitter biological blockage in drip irrigation systems. The injected chlorine dose is generally determined by chlorine concentration at the terminal of the laterals which may lead to a high concentration of residual chlorine at the front of the system and bring detrimental impact to the soil environment and growth of crops, especially in large irrigation units with long laterals. A two-season experiment was undertaken to determine the effects of chlorine disinfection and lateral length on soil NO₃-N, enzyme activities, and maize yield under wastewater drip irrigation. The experiments were constructed with lateral lengths ranging from 20 to 80 m and injection chlorine concentrations at the end of laterals ranging from 2 to 6 mg L⁻¹. Lateral length had a major impact on enzyme activities in the partial growth stage, although the effects of lateral length and chlorine concentration on soil nitrogen content and maize yield were negligible. Enzyme activity and soil nitrogen concentration decreased throughout the lateral length as a result of chlorination. A higher detrimental impact on soil characteristics and maize yield is probably going to result from a high concentration of chlorine and a long lateral length mode. The maize yield peaked at L80 with a concentration of 2 mg L⁻¹ chlorine, while it peaked at L40 with 6 mg L⁻¹ chlorine concentration. A chlorination scheme with long lateral length and low chlorine concentration is recommended in consideration of maize yield and minimizing potential negative effects on the soil environment.