Nitrate Movement in the Soil Profile under Irrigated Agriculture: A Case Study

The study was conducted at the research station of Sindh Agriculture University Tandojam where four irrigation methods installed during 2000 were utilized. The irrigation methods included traditional flooding (through basins and furrows) and micro irrigation (through trickle and sprinklers). The soil samples were collected at 0.3, 0.6, 0.9 and 1.2 m depths for nitrate nitrogen analysis. The results from two-year study showed high NO3-N concentrations at all sampling depths under basin and furrow methods, which could be attributed to free percolating water under these methods. In contrast, the NO3-N concentrations remained concentrated only in the top 0.3 and 0.6 m depths under trickle and sprinkler irrigation methods due to insignificant water movement towards deeper depths. The results further demonstrate that the NO3-N concentrations exceeded the threshold limit (i.e. 10 mg l-1 set by EPA) under basin and furrow irrigation methods but remained below the threshold limit under trickle and sprinkler irrigation methods, at 1.2-m depth. The availability of NO3-N at 1.2-m depth suggests that it will continue to move towards deeper depths under traditional methods, and consequently contaminate the shallow groundwater. The people drinking this contaminated groundwater are likely at substantial health risks