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Wet conditions in early spring can result in a loss of nitrogen (N) from the soil root profile. Rain may delay planned sidedress N applications. Pre-tassel N (PTN) applications can be used to deliver N just prior to or during the period of high demand for N in the plant. Corn plant nitrogen (N) requirements are large during the rapid growth phases (V8 thru V14) and greatest during grain fill stages. Recommended PTN applications rates typically range from 15 to 25% of total N applied to corn.1 PTN applications should be used to provide rescue N to the crop or to supplement a multiple N application strategy.
To determine N losses or crop needs prior to application, use a pre-sidedress nitrate soil test and take composite 12 to 24-inch soil samples throughout the field or within predetermined management zones.2 Optical sensors or aerial imagery can be used to assess N deficiencies and estimate needs.3
High-clearance equipment, set up to deliver N into or on the soil, can be used to band UAN while minimizing leaf burn, hydrolysis, and volatilization. Broadcasting urea with a urease inhibitor is an option but research has shown that leaf burn can be severe and reduce yield potential. Banded urea applications can help reduce injury and volatilization.
PTN applications may help recover yield potential but depending on the duration and severity of the N deficiency some yield loss may be irreversible. N deficiencies need to be detected early and PTN applications made soon after detection to provide N in time for maximum corn utilization. PTN applications have been made as late as tasseling with some success.4 Applications after tasseling are not recommended. Soil uptake of N slows after tasseling as the plant relies more on remobilized N from vegetative storage to grain.
1 Slaton, N., Roberts, T., DeLong, R., Massey, C., Parvej, M., Dempsey, R., Fryer, M., and Hayes, S. 2013. Corn yield response to nitrogen fertilization strategies with and without a pretassel application. University of Arkansas Extension Service. http://arkansasagnews.edu. 2 Bly, A. 2015. Pre Side-Dress Nitrate Test (PSNT) for Corn. iGrow. South Dakota Sate University. 3 Solari, F., Shanahan, J., Ferguson, R., Schepers, J., and Gitelson, A. 2008. Active Sensor Reflectance Measurements of Corn Nitrogen Status and Yield Potential. Agronomy Journal 100: 571-579. 4 Miller, R., Nielsen, B. and Camberato, J. 2011. Response of corn to late-season nitrogen application. https://www.agry.purdue.edu. Web sources verified 06/22/2016. 160701082332