Does late-planted corn equal less nitrogen?

By Greg LaBarge, Ohio State University

Reducing nitrogen rates by 10% is a common recommendation when corn planting dates shift to late May and June. The logic is straightforward: warmer soils increase microbial activity, accelerating organic matter breakdown and nitrogen release. In theory, more soil-derived nitrogen should reduce the need for applied fertilizer.

There are few studies on corn N response requirements; in fact, I found only one. Fortunately, it is an Ohio study where researchers tested five hybrids and four nitrogen (N) rates across early (late April/early May) and late (early/mid‑June) planting dates. Their goal was to determine whether hybrid maturity or planting date meaningfully affected the economically optimal nitrogen rate (EONR).

Key Findings Farmers Should Know

• Late planting doesn’t always mean lower N needs.

In 2006, even though late‑planted corn yielded less, its optimum N rate was nearly identical to early‑planted corn — 170 vs. 166 lb N/acre. As the authors put it, “there was… no difference in grain yield between planting dates in the absence of N fertilizer,” showing nitrogen — not planting date — was the limiting factor.… Continue reading