Effects of carbon content on transport and transformation discipline of nitrogen in soil with wastewater irrigation

To understand the impact of carbon content on nitrogen transport and transformation in wastewater irrigation systems, soil column experiments were conducted. Soil columns with ryegrass growing in them were irrigated with primarily treated effluent (high carbon content) and secondarily treated effluent (low carbon content). Samples of irrigation water, soil solutions from 10, 40 and 70 cm beneath soil surface, and drainage were collected during each irrigation event for analysis of ammonia, nitrate and total nitrogen. Dry matter yields of ryegrass were recorded and total nitrogen in them were measured. The results showed that about 34% of the nitrogen from irrigation water was uptaken by crop, 62% was removed through denitrification or deposit in the soil nitrogen pool. The amount of nitrogen that infiltrated into soil deeper than root zone was only 3% - 4% of the amount in irrigation water. For the dry matter yield and the amount of nitrogen utilized by crop, columns irrigated with high carbon content wastewater were better than columns irrigated with low carbon content wastewater. Higher carbon content was benefit to the transformation of nitrogen, its uptaken by crop and removal through denitrification.