How to Determine Nitrogen Rate Adjustments for Next Year
With this year being so dry - and most likely low yields - producers may wonder about nitrogen rate adjustments for the 2013 corn crop. University of Illinois Assistant Professor of Crop Sciences Fabian Fernandez says as a general rule - corn following soybean needs less nitrogen because the quantity and quality of the soybean residue reduces the amount of immobilization and increases the amount of nitrogen mineralization from crop residue and the soil. However - for areas heavily affected by the drought where the amount of nitrogen taken up was reduced - large amounts of unused nitrate-N are left in the field - which Fernandez says makes it difficult to estimate the amount left. He recommends using a direct method - measuring soil nitrate-N levels. To do this - he says to collect at least a 12-core composite from representative portions of the field at different positions with respect to the crop-row at a depth of two to three feet. The two-foot depth should be adequate where little nitrate movement is expected - according to Fernandez - while the three-foot depth is appropriate where rain may have moved the nutrient deeper. He says the Corn Nitrogen Rate Calculator can be used to calculate the maximum return to nitrogen. Go to extension dot agron dot IA state dot edu slash soil fertility slash nrate dot aspx (http://extension.agron.iastate.edu/soilfertility/nrate.aspx).
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