September 6, 2022
Managing soil fertility is a critical component for farmers looking to manage their costs of production. In times when nitrogen or phosphorus might be expensive on the market, it’s tempting to pull back on fertility programs. But that could be a mistake, said Lucas Haag, associate professor and Kansas State University Research and Extension agronomist at Colby.
At the end of the day, there’s still no other crop input for wheat farmers than nitrogen that offers as high of a return on investment, and the economic penalty of being short is pretty steep, Haag said during a Wheat Rx meeting in Phillipsburg on Aug. 9.
And if the wheat market is evolving to start rewarding growers for protein in their wheat, he said the economic penalty for being short on nitrogen can be greater than what you save in application. The key is knowing what your soil already has available, and applying at rates that either maintain that soil fertility or build it in your soil bank for future crops.
Know before you apply
Kansas growers may be used to just applying a standard rate of nitrogen for their wheat crop, but they could be over- or under-applying for the crop’s needs. That can be expensive, Haag said. He offered up some points growers should consider as they’re figuring their application rates:
How much nitrogen does the crop need to meet its yield goal?
How much nitrogen is in the soil profile?
How much organic matter will be mineralized?
How much nitrogen could be volatized?
Will we have carryover nitrogen from soybeans or alfalfa or another nitrogen-fixing crop?
“What we’re left with is our nitrogen recommendation to make sure we’re meeting the maximum uptake needs of that crop,” Haag said.
In an Aug. 25 Agronomy eUpdate from K-State, Dorivar Ruiz Diaz, K-State nutrient management specialist, reminds farmers who have soils prone to leaching to consider the timing of their soil tests. Soil test values from the fall may be different from those in the spring, due to leaching over the winter in these soils.
Ultimately, failure to account for the nitrogen already in your soil can waste the resource, and cause crops to put on excessive foliage, increase susceptibility to plant diseases, inefficiently use soil water and reduce their yield, according to Ruiz Diaz.
Haag also reminded growers to be realistic about yield goals for their region and their soil types. “Taking your highest, best yield ever raised and tacking another 10% onto that, that’s probably not the most economical yield goal,” he said. Instead, shoot for something in between, he added.
Haag also reminded growers that wheat needs adequate phosphorus before it can respond to nitrogen. And he said growers who have recently changed up their crop rotations to include more soybeans, rather than traditional wheat-fallow-wheat rotations, should review their phosphorus removal rates in their nutrient equations. It’s easy to underappreciate how much a good 40- to 50-bushel soybean crop can remove, he said.
“Wheat responds well to starter phosphorus, especially when late-planted,” Haag said. If you’re planting the wheat later, after you’ve harvested soybeans, you can maximize your response to starter phosphorus, he added. And the more frequent wheat appears in a cropping rotation, the more farmers should consider their phosphorus applications.
Ultimately there are obvious economic implications for dialing in the right fertilizer applications, Haag said, but there are environmental implications as well.
Many larger grain companies are trying to get a handle on carbon footprints of the crops they trade. Wheat farmers can help those companies and themselves by showing that they are managing their nitrogen and phosphorus applications.
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