Nitrogen Carryover From Corn

WI-MN Cooperative Extension Agricultural Weather Page

Introduction

In late winter and early spring, some soils in Wisconsin may hold a significant quantity of nitrogen left over from the previous crop. This residual nitrogen should be accounted for when deciding fertilizer needs, to avoid excess applications. The "Preplant Soil Nitrate Test" (PPNT) is the best way to determine how much, if any, nitrate carried-over from the previous year. In the PPNT soil samples are taken as early as possible in the spring to a depth of two feet, and sent to a soil analysis laboratory for testing.

In some years, however, we can be fairly certain that there was little nitrate in the soil profile at the end of the crop, and/or overwinter precipitation leached any residual to below the rootzone of the next corn crop. In order to save the work and expense of performing the PPNT when there is little likelihood of carryover, Larry Bundy and Mattias Vanotti of the Department of Soil Science, University of Wisconsin-Madison devised a calculation to identify years when the PPNT is not useful. The predictive relationship was based on the evaluation of long-term cropping trials at the University of Wisconsin-Madison College of Agricultural and Life Sciences Agricultural Research Station at Lancaster, WI. Descriptions of the calculation were published in:

Bundy, L.G., M.B. Vanotti, T.W. Andraski, and P. G. Widen. 1993. Predicting 1993 nitrate carryover in Wisconsin. Proc. Wis. Fert., Aglime and Pest Mgmt. Conf. 32:213-222

Three factors were found to account for most of the year-to-year variation in nitrogen carryover:

nitrogen rate applied during the previous growing season,
soil moisture status during August of the previous growing season, and
overwinter percolation (October-April) through the soil.

August soil water and overwinter percolation was estimted using a computer simulation model of hydrology called GLEAMS (Version 1.8.55), developed by the USDA/ARS. Carry-over nitrogen was assessed both by soil analysis and the yield of oat crops which were grow on residual soil nitrogen.

Nitrogen Carryover Calulator

We have created a version of the model that can be accessed over the World Wide Web. Beginning in November of each year, the model will estimate the current amount of residual nitrate in field, providing guidance for the decision to perform the PPNT prior to planting the next spring. The user must supply the soil name, county, and amount of nitrogen fertilizer applied to the previous crop.

	UNDER CONSTRUCTION

Creation of this Web-accessible version of the N carryover calculator was funded by the
WISCONSIN FERTILIZER RESEARCH COUNCIL
For more information on nitrogen carryover research,
contact Larry G Bundy at the Dept. of Soil Science, Univ. of Wisconsin-Extension
Larry Bundy, lgbundy@facstaff.wisc.edu