Corn Growth and Yield Responses to Pre-Plant and in-Season Nitrogen Combinations.

Increased variability in spring and summer weather and degradation of Great Lakes Basin water quality require improved corn (Zea mays L.) nitrogen (N) management strategies. In-season N applications may help synchronize N availability with corn uptake but further investigation is needed to validate different combinations of pre-plant and in-season N strategies. Field experiments were initiated in 2014 to investigate corn response to N management programs involving multiple N-placements, timings, and sources applied at a single N rate at two Michigan locations. Nitrogen management programs were grouped into three strategies utilizing broadcast pre-plant incorporated (PPI) N, starter N applied in-furrow (7.8 kg N ha^-1), or starter N applied 5 cm beside and 5 cm below the furrow (44.8 kg N ha^-1). Treatment combinations within the in-furrow and banded starter N strategies included sidedress at V4-6, V10-12, or 50/50 (split) V4-6 and V10-12, while PPI strategies involved 100% urea, 25/75 mix of urea with polymer-coated urea, and poultry litter applied at 2.24 Mg ha^-1 plus sidedress N V10-12. Treatments were arranged in a randomized complete block with four replications including a non-treated control. At site 1, the in-furrow starter N strategy delaying sidedress N application until V10-12 decreased mean grain yield 6.9-7.8% as compared to the V4 or split sidedress N application. Banding starter below and to the side of the furrow at V10-12 decreased grain yield 4.1-6.3%. At site 2, collectively the PPI N strategy resulted in a 3.6-4.8% yield increase as compared to the other strategies with similar yield reductions to delaying sidedress N applications until V10-12. Due to limited N losses, first year data suggest that a lack of numerous, large ( > 25mm) precipitation events may have reduced the opportunity for positive yield gains when applying V10-12 sidedress N applications.