Nitrate Concentrations in Deep Soil Cores as Related to Soil Profile Characteristics

Fifteen sites within a 30‐ha study area were studied to determine the effect of soil profile characteristics on nitrate concentrations (NO 3 − ‐N) below the root zone. The N input, crop removal of N, and water management were similar for all sites during the previous 6 years. The soils of the study area were primarily Alfisols and Entisols of fine‐loamy, coarse‐loamy, sandy and sandy over loamy families. Nitrate concentrations varied between sites and with depth. The average nitrate concentrations below the root zone ranged from 4.9 to 15.3 µg/g when expressed on an oven‐dry soil basis. Profile characteristics were significantly correlated with the average nitrate concentrations below the root zone. A regression equation relating average nitrate concentration in the 1.8–8 m depth to control section characteristics explained 86% of the variability of the NO 3 − ‐N concentration and was highly significant. Hence, to minimize ground‐water pollution, soil profile characteristics should be considered in selecting land for high N input whether by fertilization or waste disposal.