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Abstract
A three year continuous corn experiment was conducted to evaluate the use of soil nitrate nitrogen determination as a means of modifying nitrogen recommendations for corn. Three rates of nitrogen (84, 168, 252 kg/ha) were used. Nitrate nitrogen contents of the soil profile to 60 cm depth were determined several times over the three year period.
The rainfall distribution and crop demand for N appeared to have the greatest effect on soil nitrate levels at any given sampling. Quantity of nitrate nitrogen in the soil profile near planting of corn had no significant effect on corn grain yields. The analyses of samples showed seasonal and treatment changes. There were some significant carryover effects on corn yields but these effects were not measurable using only soil nitrate analysis. Coefficients of variation for the nitrate measurements went as high as 100% and were not due to laboratory procedures. The sample variability, difficulty of sampling and lack of relationship of results to corn yields makes nitrate determinations on the Udollic Ochraqualf an impractical operation for use in modifying nitrogen recommendations for corn.
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A contribution of the Missouri Agricultural Experiment Station. Journal Series No. 9497.
Professor of Agronomy, former research specialist and former graduate assistant, Department of Agronomy, University of Missouri, Columbia, MO 65211. WCR is now crop breeder, Weaver Popcorn Co., New Richmond, IN 47967. GDH is Extension Area Agronomist, Montgomery City, MO 63361.