Rainy spring weather in recent years has led many growers to move away from fall application of nitrogen (N) and toward spring application. Most growers can get N applied before planting with little trouble. However, research is showing that in many cases, particularly with rainy spring weather, in-season application can give the plant the nitrogen it needs at the time it needs it most. This was true in many locations in 2015. Here are a few issues to consider based on what we’ve learned through last year.
1. Be flexible about nitrogen application timing. It pays to be willing to apply some N by sidedressing after planting.
Based on observations over the past two growing seasons, we often see benefits from multiple N applications, including applications in the late vegetative phases of crop development.
When growers apply all of their nitrogen before planting and heavy rains follow, chances are a substantial portion of that N will be lost. Research by Tony Vyn at Purdue and Emerson Nafziger at the University of Illinois has shown that corn can respond to late-season N applications.
2. In-season application options depend on your equipment.
Most growers can use toolbars with coulters to inject liquid N into the soil after planting (32 percent UAN, for instance). This requires only a small investment, which is much less than potential yield losses if the crop suffers from a lack of N during critical development phases. In fact, DuPont Pioneer research shows modern corn plants take up 37 percent of their N need at tasseling or later. For late-season N application, growers will need highboys or aerial application, which require a greater investment.
3. In-season N application may not be cost-effective every year.
Spring rains can cause a major loss of N. However, in drier years, growers may not see as large a benefit from in-season N application in some soils. Sandy soils tend to lose N easier than soils with higher clay content. In wet years, research indicates that in-season N applications usually offer a benefit
4. Don’t make fall applications when it’s too warm.
In 2015, most growers experienced a warm fall. If you’re going to apply N in fall, consider soil temperatures and weather forecasts. If you apply when soil temperatures are 50 degrees or warmer, you can get rapid nitrification of anhydrous ammonia. An N inhibitor may help, but losses are still possible if soil temperatures remain warm for an extended period of time after application. In this case, rainfall after application can cause significant N losses. The crop will never see a benefit from the application.
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