ABSTRACT:
Dissolved N and P concentrations in surface and subsurface flows were measured from three corn-cropped watersheds in southwestern Iowa from 1974 through 1983. One watershed was tilled conventionally while the other two were till-planted, all on the contour. One of the till-planted watersheds was terraced, with underground pipe drains to remove excess water from the terrace channels. Each of the watersheds was fertilized at recommended N and P levels for optimum corn production. Losses of NO3-N, NH4-N, and PO4-P in surface runoff were low, representing less than 2% of the annual fertilizer application. However, NO3-N and NH4-N concentrations in surface runoff from the till-planted watersheds sometimes exceeded water quality standards. PO4-P in surface runoff from each of the watersheds always exceeded the water quality standard, and was especially high from the till-planted watersheds. NO3-N losses in subsurface flow represented more than 85% of the total NO3-N losses in both subsurface and surface flows. The highest annual NO3-N loss in subsurface flow was 74.4 kg/ha (66.4 pounds/acre) from the nonterraced, till-planted watershed in 1983. NO3-N concentrations in subsurface flow from this till-planted watershed have exceeded the water quality standard since 1977.
Footnotes
E. E. Alberts is a soil scientist and R. G. Spomer is an agricultural engineer with the Watershed Research Unit, Agricultural Research Service, U.S. Department of Agriculture, 207 Business Loop 70 East, Columbia, Missouri 65203. Research was conducted in cooperation with the Iowa Agricultural and Home Economics Experiment Station.
- Copyright 1985 by the Soil and Water Conservation Society
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