NEVADA, Mo. — “I brought it up to test.” University of Missouri Extension agronomist Pat Miller often hears that when farmers talk about crop fertilizer applications.
“I do not think it means what you think it means,” Miller says, quoting the movie “The Princess Bride.”
According to Miller, people who say that usually mean that they made a one-time fertilizer application recommended by a soil test.
But MU bases soil test recommendations on an eight-year buildup, Miller says. This recommended application replaces what is removed plus one-eighth of the fertilizer needed to bring the soil fertility to a good level, according to the yield goal.
“Fertilizer recommendations should be applied every year for eight years to ‘bring it up to test,’” she says. “The exception is for perennial forages where too much nitrogen and potash prevent germination of small seeds. Recommendations are reduced for the year of establishment.”
Miller says it is also important to know the correct crop and yield goal. A crop code for straight cool-season grass will recommend nitrogen. But if grasses have a good stand of clover, they do not need nitrogen. Applying it is a waste and encourages the grass to crowd out the clover, she says.
An unrealistically high yield goal may suggest too much fertilizer and a low yield goal could result in underfertilizing and underperformance. Years of little to no fertilizer cannot be fixed by a one-year application, she says. It may take several yearly applications before you see much additional crop growth, especially with phosphorus and potassium.
Soils with a low pH can tie up nutrients, so make it a priority to apply lime to those fields, Miller says. Lime also works slowly, and it can take several years to see results.
For more information, check out the MU Extension guide “Interpreting Missouri Soil Test Reports” at extension.missouri.edu/g9112. For questions, contact Miller at 417-448-2560 or millerpd@missouri.edu, or contact your local MU Extension agronomist.
Learn more about how to submit soil samples at soilplantlab.missouri.edu.
— Pat Miller
Agronomy Specialist
University of Missouri Extension
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