Nitrate enrichment in groundwater from long-term intensive agriculture: its mechanistic pathways and prediction through modeling.

Nitrate (NO(3-)N) contamination of drinking groundwater is a serious worldwide problem. We studied the mechanistic pathways of the nitrate enrichment in a drinking groundwater system of an intensively cultivated district in India and predicted the enrichment through modeling. Analysis of groundwater samples (3472) showed that the nitrate content during the postmonsoon season (0.87 mg L(-1)) was higher than the nitrate content during the premonsoon season (0.58 mg L(-1)). It decreased with increasing depth of the aquifers sampled (r = -0.38), decreasing N-fertilizer application rate (r = 0.74), increasing average root length of the cropping systems followed (r = -0.54), and their efficacy for N-utilization (r = -0.61). Soil properties (136 representative samples) like bulk density (r = -0.72), hydraulic conductivity (r = 0.56), clay (r = -0.29), organic carbon (r = 0.72), NO(3-)N (r = 0.82), and potentially plantavailable soil N (pAvN) (r = 0.82) added to the variability of its enrichment. Prediction of nitrate enrichment by multiple regression equations with selected mastervariables explained 83.6-85.8% of the variability. Results indicate that potentially plant available soil nitrogen, commonly measured for fertilizer recommendation, may help in predicting nitrate enrichment under long-term intensively cultivated alluvial agroecosystems.