Making decisions about nitrogen application can be tough. We’ve found two recent articles from Successful Farming and DTNPF on the topic and combined their recommendations into a handy list of do’s and don’ts.
Gene Johnston of Successful Farming provides some tips about nitrogen from Newell Kitchen, a soil scientist with the USDA-Agricultural Research Service in Missouri. Kitchen says it’s hard to know how much nitrogen apply because it’s an inexact science. In the past, it was common for farmers to err on the high side. He’s concerned that many farmers still do this, despite a lot of research showing that the practice is unnecessary. Up to 40% of all corn acres get 30 pounds of nitrogen that isn’t needed. It can be expensive, and it’s bad for the environment- why not put the time in to get it right?
- Use calculation tools to figure out your economically optimum nitrogen rate, or EONR. One tool, called the Maximum Return to Nitrogen Calculator, allows farmers to enter in their own nitrogen and corn prices.
- Do your own on-farm strip trials. If you live in Iowa or Missouri, you can even get a little help setting them up. Start by giving your test strips an extra 30 pounds of nitrogen from your standard whole-field rate. Give other test strips 30 pounds under, and then compare yields. If both the plus and minus strips are within 5 bushels/acre of your whole field nitrogen rate, then you can assume that you’re close to EONR. If you don’t see a yield increase in the strips where 30 pounds more nitrogen was applied, and you don’t see a yield increase where 30 pounds less was applied, you’re probably using too much. If you see a bigger yield where more nitrogen was applied, you’re probably underapplying.
Emily Unglesbee, a DTN Staff Reporter also provided some key fall fertilizing tips from a podcast on nutrient management from the University of Minnesota Extension. Her article titled, “Fall Fertilizer Tips,” has many things to keep in mind.
- Consider delaying nitrogen application as long as possible, especially in areas where fall urea is considered a best management practice. Phosphorous and Potassium are okay to apply earlier.
- Fall fertilizer application should only begin after the soil temperatures drop below 50 degrees. This helps minimize nitrification, the process where ammonia converts to nitrites, and then nitrates. Nitrates can leach. Even in more northern areas like Minnesota, it isn’t that uncommon now for large temperature swings to occur even into December. So watch the forecasts.
- Pay attention to your soil moisture. Soil that’s too wet or too dry can prevent anhydrous ammonia applicators from getting a good seal. Do one pass and go back. After a few minutes, if you smell ammonia, you know that you’re losing it. If you’re using manure, make sure that you’re fully incorporating it into the soil. Always beware of soil compaction dangers, as liquid manure tankers can be very heavy.
- Watch the wind speeds. If it’s really windy it can be difficult to get the application right.
- Know the limitations of nitrification inhibitors. They are not a “silver bullet,” and only last a few weeks. At warmer temperatures they degrade more quickly, and are less effective. And some ingredients can be more effective than others. For example, the ingredient nitrapyrin, when designed for use with urea or manure, has shown mixed results.
- Take samples. When testing for phosphorous, potassium and zinc, take a soil sample that is 6 to 8 inches deep from several different locations. Sample your manure too. This can help ensure that your calculated application rate is as accurate as possible.
- Don’t always assume that fertilizer nitrogen is related to corn yield. Kitchen says,
“Sometimes, when the right combination of weather and soil conditions comes together, you get 230-bushel yields on just 30 pounds of applied nitrogen.”
- Many of the newer hybrids don’t need more nitrogen. Some varieties have been selected because they use nitrogen more efficiently.
- Don’t apply fertilizer to frozen or snow covered soil– especially phosphorous, potassium and manure. Most manure applications will just end up washing off.
- If you ran out of time to sample your soil before fertilizer application, don’t bother measuring soon after. If you sample the soil too soon after application, your values will be inflated.