ABSTRACT:
Nitrate contamination of shallow groundwater has been widely documented in agricultural systems, especially where high rates of nitrogen (N) fertilization are used. In the Coastal Plain region of the Chesapeake Bay drainage basin, lateral groundwater discharge appears to be the major transport pathway of N from cropland into estuarine waters. The most direct approach for reducing subsurface N transport into surface waters as well as the potential for nitrate contamination of deeper aquifers is to control nitrate availability in the root zone. Soil nitrate concentrations in nonirrigated corn production systems were investigated under differing fertilization and tillage practices, as well as in the presence and absence of a rye winter cover crop. Lowest nitrate concentrations in the upper soil profile (0-30 cm) in all treatments were observed following the winter groundwater recharge period. Corn growth reduced nitrate and soil moisture levels during early summer months. But following the relatively brief period of com nitrogen use, microbial processes increased soil nitrate levels dramatically. As a result, quantities of nitrate sufficient to raise nitrate concentrations in the annual volume of groundwater recharge above the proposed drinking water standard (10 mg/l nitrate-N) were present in the root zone following corn harvest in treatments fertilized at presently recommended rates. Autumn soil nitrate levels increased as growing season N application rates increased, but were highest in unfertilized fallow treatments. Growth by rye cover crops planted immediately after corn harvest responded positively to increasing nitrate availability in the root zone, and cover crop uptake removed a major percentage of pore water nitrate from the upper region of the soil profile prior to the onset of the groundwater recharge period. The use of cereal grain winter cover crops may offer an effective management alternative to more drastic measures, such as removing farmland from production or restricting N fertilization rates, for reducing groundwater nitrate contamination and subsurface transport of N into Chesapeake Bay.
Footnotes
K. W. Staver is a graduate research assistant in the Agricultural Engineering Department and R. B. Brinsfield is head of the Wye Research and Education Center and affiliate assistant professor, Agricultural Engineering Department, University of Maryland, Queenstown, 21658. Thus study was conducted by the Maryland Agricultural Experiment Station with financial support through a Cooperative Agreement with the Soil Conservation Service, U.S. Department of Agriculture, and USDA Low Input Sustainable Agriculture Program Contract No. 88-Coop-1 3524.
- Copyright 1990 by the Soil and Water Conservation Society
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