Nitrate Contamination of Groundwaters in Haryana Is Nitrogen Fertilisation Responsible?

摘要

Investigations of randomly collected tube well water samples from Khera Jhanjrola, Mehendwara and Dhankot villages of Gurgaon district revealed that majority of the wells in Khera Jhanjrola (54 %) had NO3 concentration beyond 50 mgL~(-1). Pumping test at different discharge rates suggested that the aquifer was semi-confined and not much variation in nitrate content of pumped water with pumping rate and duration. There was high total N (0.14%) with not much variation in different layers in profile up to 15m and more than 95% of the total N was in organic forms being a result of saturation of the soil's column by nitrate consequent upon irrigations with nitrate rich waters. Available N was < 250 kg ha~(-1) throughout the soil profile of 15m. Organic C at different depths was close to the average value for the whole profile. Results of spatial and temporal variation (pre- and post-monsoon) showed not much variation in the nitrate (slightly higher in pre-monsoon than in the post-monsoon) whereas EC differed considerably. A positive correlation indicated a general increase in NO3 as EC increased. Calibrated and validated model (LEACHN model) predicted leaching to the tune of 3.1 in pearl millet and 9.6 kg ha~(-1) in wheat meaning losses as nitrate to the tune of 13 kg ha~(-1) yr~(-1). Simulated nitrate leaching under normally practised irrigation depth was 9.0 and 32.8 kg/ha for pearl millet and wheat, respectively with nitrate rich waters. With more efficient irrigation (depth of 40 mm), simulated nitrate losses decreased to 6.0 and 13.7 kg/ha for pearl millet and wheat, respectively. In -situ measurement of nitrate movement in the profile, measured values of nitrate leaching at 30, 60 and 90 cm soil depth was 27.86, 28.95 and 23.19 kg/ha, respectively. The model predicted nitrate leaching at the rate of 33.3 kg/ha at 120 cm and predicted and actual measured values exhibited a reasonably good agreement. Results indicated that leaching from fertilisers might not be a major contributing factor to high NO- concentration in groundwater at theselected sites.