IN THE FIELD Field day attendees watched equipment made to incorporate fertilizer for off-season application while only disturbing a small amount of soil in each field row. Farming systems, available equipment, location, and other factors will also determine timing of nutrient application. In reality, some fall and spring application will have to occur. Knowing what conditions are important in the fall or spring to prevent nutrient loss is the way to improve nutrient efficiency and protect water resources.
Considerations for fall
APPLICATION IN THE OFF-SEASON When applying nutrients outside of the growing season, certain practices can help minimize losses. by Amber Radatz
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utrient applications, from either manure or fertilizer, come with an ever-growing list of items to consider before, during, and after application. Many of these considerations are related to field characteristics or weather and changing seasons. Since 2001, the Discovery Farms programs in Wisconsin and Minnesota have collected and analyzed water quality data from privately owned farms to develop solutions with farmers for the best ways to protect and preserve water quality resources. Discovery Farms is a farmer-led, water quality research and outreach program led by the University of Wisconsin-Madison Division of Extension in Wisconsin and the Minnesota Agricultural Water Resources Center in Minnesota.
There is tremendous power in understanding the conditions that lead to runoff and risk for nutrient loss. Using that knowledge to make small tweaks can pay big dividends toward achieving sustainable levels of nutrient loss.
Depends on the nutrient The best time outside of the growing season to apply nutrients depends on the nutrient of concern. In general, nitrogen is best applied close to when the growing crop will use it. This favors spring application. For phosphorus, spring applications can be a higher risk due to elevated moisture conditions and larger storm events, which correspond to more surface runoff. This favors phosphorus application during the drier conditions of fall.
6 | Journal of Nutrient Management | August 2021
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Fall can be an excellent time to apply fertilizer or manure. Compared to spring, fall usually has drier conditions and more time for fieldwork. Drier conditions lead to a lower risk of loss via surface runoff. However, without a few extra targeted management steps, fall application can lead to elevated loss of nitrogen. For applications of fertilizer or manure with high levels of nitrogen, waiting for the soil to cool below 50°F reduces the amount of nitrogen that might be converted to the nitrate form. The reason for this slower conversion of nitrogen in the soil is attributed to reduced microbial activity because of cooler soil conditions. Nitrogen in the form of nitrate moves freely with water. It is easily leachable through the soil profile and lost to shallow groundwater or subsurface tile drainage before the intended crop can utilize it. Nitrification inhibitors can provide a week or two of protection in the fall if soil temperatures haven’t dropped below 50°F. Products with known efficacy for inhibiting nitrification are dicyandiamide, nitrapyrin, and pronitradine. These chemical compounds temporarily reduce populations of bacteria in soil that are responsible for converting different forms of nitrogen to nitrate. If nutrient application is earlier in the fall where longer protection is needed for higher soil temperatures, cover crops can be planted to take up some of the applied nitrogen. Spring can also be an excellent time for fertilizer or manure applications. Surface runoff risks are higher, though, because soils are typically wetter and storms are more intense and frequent. jofnm.com
7/22/21 9:22 AM
