Nitrate pollution of ground water and impacts of nitrogenous fertilizers and irrigation on dynamics of NO3-N movement in soils of Punjab, Pakistan

Increase in N application rates may eventually raise the potential groundwater N-pollution. This survey study was conducted by Soil Chemistry Section, ISCES to assess the NO3 contents of soil from 0 to 120 cm depth with different intervals. For this purpose, the soil and water samples were collected from Okara, Vehari Sialkot, Chiniot, Hafizabad, Sahiwal and Multan districts. The results showed that nitrate leaching occurred but it is only up to 2 feet soil depth. The NO3-N contents were maximum at two upper depths (i.e. 0-30 cm and 30-60 cm) and then decreased gradually downward. The highest average NO3-N content was found at 0-30 cm soil depth and the lowest were found at 90-120 cm. The data also revealed that mean NO3-N content at 0-30, 30-60, 60-90 and 90-120 cm depths were 16.85 +/- 4.05, 15.21 +/- 4.77, 9.94 +/- 3.36 and 6.54 +/- 2.62 mg kg-1, respectively, whereas NO3-N content at same depths were ranged from 11.50-26.20, 6.53-21.15, 5.24-16.12, 1.45-9.36 mg kg-1, respectively. The results regarding underground water samples (tube well) from the same sites from all the three districts showed that NO3 were found in all the water samples but it was only in traces and their concentration were not much higher to create the health hazardous problem owing to NO3 leaching. The data showed that the highest NO3 contents did not exceed than 8.61 and 10.6 ppm in Multan and Sahiwal districts respectively, which were much lower than permissible limit i.e. 50 ppm (FAO). Similarly, the nitrate content in underground water are well below the maximum admissible limit of WHO i.e. 50 mg L-1.