The Effects of Treated Wastewater on Soil Nitrogen Dynamics and Winter Wheat Growth under Different Groundwater Depth

The reuse of treated wastewater for irrigation has become increasingly common in some areas of China due to water scarcity. Treated wastewater has high nitrogen and phosphorus content, which have negative impacts on soil and may pollute groundwater. Lysimeter studies were conducted with different groundwater depths (2m, 3m and 4m) and irrigation water (90mm and 120mm) to assess the effects of irrigation with treated wastewater on soil nitrogen dynamics and winter wheat growth. The results indicated that the nitrate nitrogen (NO3-N) concentration in both soil and groundwater increased substantially after irrigation. The increment of NO3-N concentration in groundwater depended on groundwater depth and irrigation water. When 90mm wastewater was applied, NO3-N concentrations observed in groundwater at three groundwater depths (2m, 3m and 4m) increased separately by 34.7%, 24.9% and 20.9%; while when irrigation water increased to 120mm, the values were 58.4%, 39.0% and 27.2% respectively. This reveals that groundwater depth had a significant influence on accumulation of NO3-N in groundwater, and smaller groundwater depth resulted in a higher risk of NO3-N pollution. Our study also reveals that treated wastewater encouraged winter wheat growth and improved the yield.