Spring is officially here, and with it the uncertainty of spring rains or late snow showers. For many Nebraska farmers, finishing preparation for planting or waiting on the starting line to plant is the number one priority. Nitrogen (N) management may not be the most important thought crossing their minds. But, now is a great time to think about N management for this upcoming season. The uncertainty of spring weather is a constant reminder that there are things we can and cannot control. We certainly cannot control the weather, or how much rain we get, but we can control how much N we apply and when. The best way to think about N management is managing risk.
Nitrogen is a mobile nutrient in the soil that can be lost through:
- leaching below the root zone with excess moisture,
- denitrification to the air in waterlogged soils (ponded water situations), and
- volatilization of urea-containing fertilizers that are not incorporated by moisture within several days of application.
Corn needs N to grow and yield well, so ensuring N stays in the root zone and available to the growing crop is essential. So, what is the best way to manage the risk of losing N? Ideally, small amounts of N would be applied many times throughout the season. This essentially mimics fertigation; however, if fertigation is not available, there are many other options.
The best option will, of course, depend on your operation, but minimizing exposure risk of your applied N is essential to reducing the amount of N needed to reach an economic optimum rate. In other words, sidedress most of your N in season if at all possible when the crop is actively taking up N (V8-VT growth stages) (Figure 1).
Nitrogen will still need to be applied early in the season. In that case, consider using inhibitors. Our colleagues at North Dakota State University have an excellent resource that goes through the various inhibitors and their efficacy: Nitrogen Extenders and Additives (SF 1581) by soil scientist D.W. Franzen.
But, how do we choose a rate of N to apply?
Fertilizer Suggestions for Corn (Nebraska Extension EC117) is an excellent resource that walks a user through calculating an N rate for the upcoming season using the UNL algorithm. We also have an Excel calculator, the UNL Corn Nitrogen Calculator for Nebraska, that helps step through this same algorithm. It and other soil management resources are available in the Soil Management section of CropWatch.
But, with all methods, there are fail points. The UNL algorithm is an effective guide to determining N rate, but it is only a starting point. Conditions change during the season and if they become conducive to N loss, appropriate management will be needed to react and adjust.