Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu
This project evaluated how planting timing and starter nitrogen (N) plus sulfur (S) applications influence early-season growth, nutrient uptake, and yield in corn. Corn was planted in April, May, and June with five starter N+S rates, and monitored using tissue testing and drone based canopy sensing.
Planting timing was the primary driver of yield. Mid-May plantings produced the highest yields, while April and June were significantly lower. Starter N+S improved early tissue N and S—especially in April and May when cooler soils limited mineralization—but these benefits did not translate into yield increases. June-planted corn showed the lowest tissue N levels but minimal response to starter fertilizer, suggesting warmer soils supplied sufficient early-season nutrients.
Overall, starter N+S enhanced early nutrient status but had limited influence on final yield compared with planting timing and in-season N uptake. These results highlight the importance of aligning nutrient strategies with planting date and seasonal conditions.
Figure 1. a) Yields by averaged across starter treatments by month where differences are significant at alpha = 0.05 and b) yields by N/S rate each month, where there were no significant differences.