Evaluation of In‐Season Nitrogen Management Strategies for Corn Production

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.