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NITROGEN MANAGEMENT

Evaluation of In-Season Nitrogen Management Strategies for Corn Production

^a Dep. of Agronomy, Kansas State Univ., Manhattan, KS 66506-5501
^b Dep. of Agronomy, Iowa State Univ., Ames, IA 50011-1010
^c Farm Services Agency, Epworth, IA

^* Corresponding author (ruizdiaz{at}ksu.edu).

Nitrogen is an important and costly input for corn (Zea mays L.) production. With rising prices and environmental concerns, producers are looking for ways to better manage N fertilization. A project designed to evaluate in-season N management strategies for adjusting N rate was conducted in 30 Iowa cornfields from 2004 to 2006. Nitrogen rates applied preplant or early sidedress (PRE-N) and corn plant sensing with a chlorophyll meter (CM) to detect N stress was used to determine as-needed in-season post sensing nitrogen application (POST-N). Field-length strips were replicated three times with six N treatments: zero-N control, 67 kg N ha^–1 (reduced PRE-N rate), 67+ (reduced PRE-N rate plus POST-N), 134 kg N ha^–1 (agronomic PRE-N rate), 134+ (agronomic PRE-N rate plus POST-N), and 268 kg N ha^–1 (PRE-N non-N limiting reference rate). Nitrogen deficiency stress sensing was partially successful, with 70 to 80% correct N deficiency detection. Mean yield increased 0.5 Mg ha^–1 across all sites with the POST-N applied to the 67 kg N ha^–1 PRE-N rate. The 67+ POST-N strategy had a similar total N applied as the agronomic 134 kg N ha^–1 PRE-N rate, but the yield was 0.5 Mg ha^–1 lower. This indicates yield potential loss and poor recovery from the POST-N applications. Economic return comparisons indicated that the agronomic 134 PRE-N rate and 134+ POST-N in-season strategy were similar and had higher return than the 67+ POST-N strategy. The agronomic PRE-N rate, with confirmation of N stress and determination of additional N need through plant sensing, was a more cost effective in-season strategy than starting with the reduced PRE-N rate.

Abbreviations: CM, chlorophyll meter • EONR, economic optimum nitrogen rate • POST-N, in-season nitrogen applied after plant nitrogen stress sensing • PRE-N, nitrogen applied preplant or early sidedress • RCM, relative chlorophyll meter • UAN, urea-ammonium nitrate solution.

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Received for publication May 19, 2008.