Update from the Field: Keep it Cool
Posted by Dave Dyson, Agronomist on November 05, 2019
Fall application of nitrogen has quite a few advantages over a spring application, if done properly. The time savings can be the difference between planting a crop on time or fighting a late-planted crop all season. Growers have had a hard time applying enough nitrogen the last few years due to weather conditions. To compound the situation, anhydrous ammonia had to get side-lined this last year due to the time constraints. This is regrettable because the stability and cost-effectiveness of anhydrous ammonia is second to none. As a result, it’s important growers put together a plan to apply enough nitrogen to feed the 2020 crop.
Let us look at the benefits for applying nitrogen in the fall. The big one is time management. Fall application is beneficial for growers with limited time in the spring. Typically, spring can be wet, and when the ground is fit to apply nitrogen, you should be planting. Applying fall nitrogen will free up time to plant your crop. It will also help to avoid compaction in your fields. Fall soils are usually dryer and lead to less compaction than knifing into wet spring soils. Cost can be a major factor as well, as anhydrous ammonia will be least expensive in the fall.
The only drawback with applying nitrogen in the fall is the chance of losing one of the most expensive inputs in a cropping operation. Once nitrogen is applied to the soil, microorganisms start converting the nitrogen from a stable ammonium form to an unstable nitrate form, Figure 1.
Figure 1: This chart shows the nitrogen cycle. The ammonium (NH4+) is injected into the soil and can either be taken up by the plant or converted to nitrate (NO3-) by the soil microorganisms. A nitrification inhibitor will prevent the NH4+ from converting into NO3-, allowing the plant to absorb nitrogen but not allowing the nitrogen to leach or move into the air through denitrification.
The nitrifying bacteria will continue this conversion until the soil temperature drops down below 40 degrees Fahrenheit. Waiting for the soil temperatures to drop below 40 degrees may be challenging, so the general recommendation is to wait for the soils to drop below 50 degrees Fahrenheit and add a nitrification inhibitor like N-Serve®. I have been checking the soil temperature for the last week, and we are averaging around 45 degrees Fahrenheit in northern Indiana.
Anhydrous ammonia released into the soil acts as a powerful sterilizing agent. It spreads out into the soil, and as it changes from a liquid to a gas, it kills most living things in the soil. This means that microbes need to grow back into the depleted application band. Allowing the microbe population to grow back takes a fair amount of time at cool soil temperatures, providing adequate time for enough bacteria to be present for nitrification to continue.
In conclusion, applying nitrogen in the fall can save you time and money, while reducing compaction normally associated with injecting nitrogen in the spring. There are two significant processes we can employ to safeguard your investment. First, be sure to wait until the soil temperature is below 50 degrees Fahrenheit. Second, apply a nitrification inhibitor with your nitrogen.
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Dave Dyson is a regional agronomist for The Andersons’ Farm Centers which are located throughout Ohio, Michigan, and Indiana. He is an Indiana native and grew up on a dairy farm in Miami County. A graduate of Purdue University with a degree in Crop & Soil Science, Dave has a deep knowledge of various agronomic topics and is committed to helping growers improve their crops. If you have any questions, Dave can be reached at david_dyson@andersonsinc.com.
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