Effective nitrogen application for fall crops

By Scout Nelson

Fall is a crucial time for fertilizer application, but warm temperatures and dry conditions can pose challenges. Applying nitrogen (N) fertilizers too early in fall can lead to losses, reducing efficiency and increasing costs. Soil temperatures play a critical role in deciding the best time for fertilizer application.

According to research, the general guideline is to wait until soil temperatures at a 4-inch depth fall below 50 degrees Fahrenheit during the early morning hours. This reduces the risk of nitrogen being transformed into nitrate, which is easily lost through leaching or denitrification.

Warm weather can push soil temperatures back up, making it risky to apply fertilizers too early. Experts recommend checking soil temperatures regularly or using data from local agricultural weather networks.

There are different guidelines depending on the type of fertilizer and application method. Anhydrous ammonia can be applied soon after the soil temperature consistently falls below 50 degrees Fahrenheit. Banded urea applications should wait about a week, while broadcast urea should be delayed for at least two weeks.

Nitrification inhibitors can be used to reduce the risk of nitrogen losses. They help slow down the conversion of ammonia to nitrate, especially in delayed soil freezing conditions. However, these inhibitors should not be used to apply fertilizers earlier than recommended. Nitrapyrin works best with anhydrous ammonia, while DCD is effective for urea products.

Delaying nitrogen application later into the fall and splitting it between fall and spring can help reduce losses and improve efficiency. Following these science-based practices will maximize crop yield and make fertilizer application more effective.

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