Testing soils to improve yields

Posted March 20, 2015

Even before Florida Georgia Line saluted it in song, Kansas wheat farmers knew the importance of their soil, particularly to their bottom line. But while “you bet your life on it,” too many farmers do not regularly test their soil nutrient levels. If they did, Dr. Dave Mengel, supervisor of the Kansas State University Soil Testing Laboratory and professor of soil fertility and nutrient management, said farmers could more efficiently apply nutrients – saving input costs and maximizing yields.

At Farm Journal’s Wheat College on February 24 in Manhattan, Mengel outlined how producers can best utilize long-term soil testing to develop that critical nutrient management system. But first, Mengel said farmers should start with a soil sample.

Mengel explained every plant requires 17 essential elements, but the relative importance of those nutrients varies between crop species. For wheat, the most critical elements are nitrogen, potassium, sulfur and chloride. In Kansas, Mengel said that sulfur and chloride deficiencies are becoming more common and that low pH levels are an even larger concern.

You Get Your Hands In It

To measure the levels of these nutrients, Mengel recommended taking soil samples at two or three different depths to capture nutrient levels for different elements. This includes a surface sample from 0 to 6 inches to measure pH, lime, organic matter, phosphorus, potassium and zinc. A second profile sample from 0 to 24 inches measures nitrates/nitrogen, sulfur and chloride. Mengel said no-till producers should consider an additional 0 to 3 inches sample to match pH and lime recommendations for no-till fields.

“Take samples early enough that you can develop a nutrient management system,” Mengel said, suggested producers should take samples between November and March. Mengel explained that 10 to 20 soil samples for an average field is ideal.

Moving forward, Mengel suggested producers sample fields regularly every one to three years, depending on crop rotation. He added that producers should sample consistently – that means in the same area at the same time of year.

For test results, farmers can either submit soil samples to their local county extension agent or directly to the K-State Soil Testing Laboratory, based in Throckmorton Hall. Find resources and cost of services at http://www.agronomy.k-state.edu/services/soiltesting/.

To maximize yields, Mengel recommended that producers keep nutrient levels in the most appropriate range for the most sensitive crop in the rotation. K-State will provide recommendations for both plant sufficiency and building soil health back to producers with the results of their soil samples.

Not Just Dirt

But, Mengel cautioned that producers should not rely solely on soil tests for their field monitoring.

“Making decisions on soil tests alone is probably not the best thing to do. There are other tools you can use too,” Mengel said, recommending that farmers also utilize yield maps, topography maps and other information in order to build layers of management for each field.

While regular soil samples are just one tool for monitoring crop health, following Mengel’s recommendation to watch long-term trends in soil nutrients can help farmers minimize cost, maximize yield and build healthier soil for the next generation of dirt lovers. 

By Julia Debes