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Fall nitrogen fertilizer application: The what, where, when and how

By: Fabian Fernandez, Extension nitrogen management specialist Crop harvest is progressing quickly in Minnesota due to the dry conditions. As soon as the crops are out, it is time to start field activities to prepare fields for next year. One of these activities might include nitrogen fertilization. What to apply? In my recent blog post on nitrogen best management practices , I discussed the fact that, for fall applications, the only source that is reliable enough is anhydrous ammonia. This is because all other commercial nitrogen fertilizers have a high potential for loss when applied so far in advance of crop uptake. The reason anhydrous ammonia works for fall applications is that, when ammonia (NH3) is injected, it disperses in the soil, reacting with soil moisture (H2O) within a retention zone, which, depending on soil moisture, can be around three to six inches in diameter. As NH3 reacts with H2O, it forms NH4 and OH-. The OH- creates a temporary increase in soil pH that inhibits
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‘Stick to what you know for sure’: High fertilizer prices call for greater awareness of nitrogen BMPs

By: Fabian Fernandez, Extension nitrogen management specialist With high fertilizer prices, farmers are looking for alternatives to make every pound of nitrogen (N) fertilizer count. To be as efficient as possible with nitrogen, the most important thing to do is to rely on best management practices (BMPs) that have been proven through years of unbiased research. While the discussion is often centered around nitrogen rate, it is important to recognize that nitrogen BMPs encompass much more than just rate. Applying the correct rate of nitrogen while being careless with which nitrogen source you use, fertilizer placement, or timing can lower your nitrogen use efficiency, and therefore your profitability, especially when fertilizer prices are high. In fact, the entire database that we use to calculate the maximum return to nitrogen (MRTN) rate was generated with research trials that use several N rates applied using BMPs. For example, there are no data points from fall nitrogen applicati