Don’t forget to test for potassium, the most important nutrient in beans

• By Fred Miller •

trent roberts
Division of Agriculture soil fertility specialist Trent Roberts shows symptoms of potassium deficiency in rice during a video about the importance of the nutrient in Arkansas row crops — photo courtesy University of Arkansas

Potassium, or potash, is an important nutrient for Arkansas’ major row crops, and a deficiency of it can significantly reduce yields at harvest.

A video, “Potassium Deficiency in Row Crops” from the University of Arkansas System Division of Agriculture, explains the importance of potassium fertilizer to Arkansas crops and how growers can make sure their plants have enough of the nutrient to maximize their yield potentials.

Potassium aids in water regulation in plants, said Trent Roberts, associate professor of crop, soil and environmental sciences for the Division of Agriculture.

“It’s essential for a lot of the pathways tied to water and water regulation, including transpiration, canopy temperature, carbon dioxide capture, and others,” Robert said.

Nitrogen fertilizer is often the focal point of most row crop systems, and potassium is sometimes neglected. “We know if we don’t put sufficient nitrogen on our crops we can’t expect to maximize the yields,” he said. “But most row crops need as much or more potassium in their above-ground tissue as nitrogen.”

Inadequate potassium nutrition can limit yields, similar to inadequate nitrogen, Roberts said. And for legumes, like soybeans, which absorb nitrogen from the air and convert it into a nutrient through nitrogen fixation, potassium becomes the most important fertilizer nutrient for most legumes to ensure optimum yields.

Roberts said light textured soils, like silt loam and sandy soils, tend to be potassium deficient. “These are the ones where proper potassium management is going to be most crucial,” he said.

Clay soils usually have adequate soil-test potassium for Arkansas crops.

“The first step to detecting and correcting potassium deficiency is soil testing,” Roberts said.

Decades of research by the Arkansas Agricultural Experiment Station, the Division of Agriculture’s research arm, has resulted in calibrated soil test-based data that allows the Soil Testing and Research Laboratory to provide accurate fertilizer recommendations, he said. Soil testing, available from the Division of Agriculture’s Soil Testing Program, can help growers know how much potash they need to apply before planting their crops.

“This is the first step to ensuring that potassium will not be limiting and helps get the crop off on the right foot,” Roberts said.

He said farmers should contact their county extension offices to obtain soil testing information, supplies and services.

Growers should follow up during the growing season by scouting their fields to look for signs of potassium deficiency, but beware of “hidden hunger,” Roberts said. Insufficient potassium can cause yield-limiting deficiencies in crops before visible symptoms appear.

Hidden hunger can be avoided by testing tissue samples from crop plants to identify potassium deficiencies during plant growth, he said. These can be submitted for analysis through the county extension offices and will let farmers know if mid-season potash applications are needed.

Often, Roberts said, yields can be recovered if potassium deficiency is detected early in the season and corrected with mid-season potash applications.

In the “Potassium Deficiency in Row Crops” video, he gives more detailed information about the effects and symptoms of deficiency in corn, rice, cotton and soybeans, how to scout for symptoms and ways to avoid or correct it.

Roberts said more information on potassium management can be found in Division of Agriculture fact sheets and crop handbooks. These are available for download from the Cooperative Extension Service: https://www.uaex.edu/farm-ranch/crops-commercial-horticulture/default.aspx

Funding support for the video and potassium research was provided by the Arkansas Fertilizer Tonnage Fees, Arkansas Rice Checkoff, Arkansas Soybean Checkoff, and Arkansas Corn and Grain Sorghum Checkoff programs.

A second video focusing on the more complex interactions of potassium in soybeans will be available soon, Roberts said.

Fred Miller is a University of Arkansas science editor. He may be reached at fmiller@uark.edu.

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