Nitrate nitrogen in surface waters as influenced by climatic conditions and agricultural practices

Subsurface tile drainage from row-crop agricultural production systems has been identified as a major source of nitrate entering surface waters in the Mississippi River basin. Noncontrollable factors such as precipitation and mineralization of soil organic matter have a tremendous effect on drainage losses, nitrate concentrations, and nitrate loadings in subsurface drainag e water. Cropping system and nutrient management inputs are controllable fa ctors that have a varying influence on nitrate losses. Row crops leak subst antially greater amounts of nitrate compared with perennial crops; however, satisfactory economic return with many perennials is an obstacle at presen t. Improving N management by applying the correct rate of N at the optimum time and giving proper credits to previous legume crops and animal manure a pplications will also lead to reduced nitrate losses. Nitrate losses have b een shown to be minimally affected by tillage systems compared with N manag ement practices. Scientists and policymakers must understand these factors as they develop educational materials and environmental guidelines for redu cing nitrate losses to surface waters.