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Research Highlights

Research Highlights
Improving potassium deficiencies in Kansas soils

Soybean response to P and K, 2019, in Kansas research fields. Photo: Dorivar Ruiz Diaz.

By Carol Brown

It is a given that soybeans need nutrients to grow, especially phosphorus and potassium. But weather and environmental stress situations can cause plants to have shortages in these nutrients. Scientists across the nation are working to improve nutrient usage in all commodity crops, including soybeans.

In Kansas, Dorivar Ruiz Diaz is studying in particular how to improve soybean uptake of potassium to avoid plant deficiency and improve yield. The Kansas State University agronomy professor is hoping to improve soybean yield in regions of the state with known potassium deficiencies, and these areas are growing.

“Potassium deficiency is becoming more common in Kansas, especially in areas where the yields are good as the soybeans can use quite a bit of potassium,” he said. “A challenge with this issue is the tests we currently use to measure soil potassium levels don’t work very well in certain soils.”

Ruiz Diaz is in the second year of a research project to improve diagnostic tools and yield response for potassium management in soybeans. The research project is supported by the Kansas Soybean Commission.

“The eastern part of Kansas has soil types that are heavier in clays and traditional soil testing methods don’t perform well in these conditions,” Ruiz Diaz said. “We’re evaluating different methods to test soils for potassium as well as why soybeans may exhibit deficiencies even when traditional soil tests show sufficient levels.”

Figure 1. Soybean yield with applied K and P.

Several factors can be determined as to why soybeans are potassium-deficient such as soil physical properties inhibiting root development or pests could disrupt nutrient uptake, Ruiz Diaz said. Although his project is focused specifically on soil fertility.

He is conducting soil tests with the widely used ammonium acetate and Mehlich-3 methods, which involves a chemical process in a lab to extract nutrient levels from the soil. He also is testing ion exchange resin strips. These are inserted across soybean fields and stay in the ground for a certain number of days. The strips will provide an indication of how much potassium is available in the field at that time. Results on these soil test comparisons are being reviewed.

Ruiz Diaz’s potassium yield response tests are being conducted on plots at multiple locations across the state. Each location has plots with no applied potassium compared with applied potassium at a high rate of 150 lbs/acre. In 2019, in the areas with potassium deficient soils, soybeans demonstrated increased potassium uptake across the growing season. The best yield increases were in plots receiving higher potassium rates plus phosphorus fertilizer.

Ruiz Diaz is conducting these tests again this cropping season with an added component to evaluate in-season potassium application.

“Typically, potassium is applied pre-plant or even the fall before, but if farmers are seeing potassium deficiency, can we do something in mid-season? What kind of benefits will there be with yield?” he asked. “This year we added plots treated with an in-season application of dried potash fertilizer; and there are encouraging results. Farmers can benefit from this repair application.”

Figure 2. Soybean yield (bu/ac) with in-season K application; average of four locations in 2019.

Ruiz Diaz’s research is showing positive results for fields that have some potassium deficiencies. Kansas farmers are benefitting from the research results through increased yields. Possibly, his research results could be applied to other regions where similar deficiencies and soil types occur.

To find research related to this Research Highlight, please visit the National Soybean Checkoff Research Database.