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Nitrogen Losses from Soils of the North Carolina Coastal Plain¹

ABSTRACT

Nitrogen balances were measured for a moderately well-drained and a poorly drained soil in the North Carolina Coastal Plain to evaluate the effect of drainage on the fate of unutilized fertilizer N. Approximately one-half of the fertilizer N applied to each soil was not utilized by the crop.

Most of the nitrogen lost by surface runoff from both soils was organic nitrogen associated with the sediment. However, there was a measurable increase in loss of nitrogen from fertilized plots as compared to unfertilized plots. The poorly drained soil (27% organic matter) had approximately 50% less surface runoff than did the moderately well-drained soil (2% organic matter). However, the concentration of N in runoff from the poorly drained soil was almost twice as great resulting in nearly identical N losses from the two soils. Much of the total surface loss of N from corn (Zea mays L.) occurred during the first few months after planting.

During the winters after the 1972 and 1973 harvests, an average of 46 kg NO₃-N/ha moved from the moderately well-drained soil by subsurface drainage. A portion of this loss entered surface waters directly via tile outlets. The remainder was thought to enter a shallow aquifer and is believed to ultimately move with the water to nearby surface streams. It is unlikely that denitrification removed significant amounts of N from the moderately well-drained soil.

An average of 16 kg NO₃-N/ha was removed from the poorly drained soil by subsurface drainage during the two winters. The smaller loss from the poorly drained soil was thought to result from denitrification of residual NO₃ in the shallow ground water.

Key Words: soil nitrogen balance • denitrification • nitrogen in drainage waters

¹ Paper Number 4504 of the Journal series of the North Carolina Agric. Exp. Sta., Raleigh, NC 27607. The work upon which this publication is based was supported in part by funds provided by the Office of Water Resour. Res. Inst. of the Univ. of North Carolina as authorized under the Water Resources Research Act of 1964.

² Graduate Research Assistant, Associate Professor, and Professor, respectively, Soil Science Dep., North Carolina State University.

Received for publication October 16, 1974.