Dry conditions and the winter that wasn’t is accelerating nutrient management decisions. Should farmers be applying fertilizer now?
“If phosphorus, potassium or lime didn’t get applied last fall, this could be a good time to get that done,” according to Dr. Dan Kaiser, University of Minnesota Extension nutrient management specialist. Without any rainfall, however, the fertilizer will just sit on the soil surface. Since it needs time to dissolve, there is some risk of loss before that occurs.
Farmers could also consider applying anhydrous ammonia. Nitrification inhibitors (NIs) could help prevent nitrogen loss, particularly in south central Minnesota. As we get closer to planting, the advantage of applying anhydrous with an NI decreases.
What about urea? “The thought of applying urea right now concerns me,” states Kaiser, “even if it was applied with a urease inhibitor.” The lifespan of a urease inhibitor spans roughly two weeks, so the potential for volatility losses would significantly increase as the inhibitor degraded. In addition, there might be enough moisture for the urea to start dissolving in the dry conditions, but it might not be enough to incorporate it. Because the loss potential is so high, an early application of urea is not recommended. Anhydrous ammonia would make more sense at this point and would be a safer bet for an early application.
“Crop producers might also consider taking preplant nitrate soil tests (PPNT) this spring before planting and any nitrogen applications,” states Jeff Vetsch, researcher at the University of Minnesota Southern Research and Outreach Center. This soil test measures residual nitrogen and can help determine how much fertilizer nitrogen is needed for this year’s crop. “However, I would wait until April to take the samples, if I could, in case there are leaching events between now and then,” he adds. The PPNT is recommended in western Minnesota, due to its drier climate. In south-central, southeastern and east-central Minnesota, the PPNT is recommended if conditions favor residual N, such as a history of manure, corntinous corn or low levels of precipitation.
Potassium has a dynamic nutrient cycle, much like nitrogen, with soil test levels fluctuating as much as 100 ppm over the growing season. If there’s moisture, water moving through the residue will leach some of the potassium out, but that differs by crop. In drier years, the amount of K that is leached out of crop residue is reduced and soil test K values can also decline. However, Kaiser predicts that we’ll see some recovery with wetter years. The bottom line is to trust your soil test results and try to sample at the same time to minimize the effects of seasonal variability.
Nutrient cycles are complex and managing them to optimize production and minimize environmental impacts is key. “In the final analysis, it comes down to whether there are enough nutrients for the crop to optimize yield,” concludes Kaiser.
For more information from University of Minnesota Extension, visit extension.umn.edu/crop-production.