Texas Tech University

Researcher Awarded USDA-NIFA Grant to Study Potassium Sorption and Fixation in Agricultural Soil

By: George Watson 

The results of the research by Matthew Siebecker and Katie Lewis could help agricultural producers better apply fertilizer to enhance productivity.
The application of fertilizer and how well it is absorbed into the soil is critical to all crop growth, but particularly when it comes to cotton. Being able to uptake the nutrients applied, however, relies on numerous factors, not the least of which are the chemical reactions that occur within the soil upon application.

One of the most crucial of those nutrients needed for growth is potassium. But the bioavailability, or the amount that is effectively taken in by the plant, of potassium can be problematic, particularly due to potassium fixation. Fixation occurs when potassium ions bond with clay particles in the soil. This can limit the amount of potassium available for uptake by the plant.

In an effort to understand the factors that chemically determine potassium fixation in soil, Texas Tech University researcher Matthew Siebecker, an assistant professor of applied environmental soil chemistry in the Department of Plant and Soil Science (PSS), will conduct a series of experiments with nanoparticle and micron-sized silicon and aluminum oxides and clay minerals to better understand these reactions.

To aid in this research, Siebecker and co-principal investigator Katie Lewis, an associate professor in PSS who holds a joint appointment with Texas A&M AgriLife Research, received a $335,489 grant from the United State Department of Agriculture (USDA) National Institute of Food and Agriculture's (NIFA) Cooperative State Research Education & Extension Service.

"We are extremely grateful to the USDA for funding our work," Siebecker said. "One of the main goals is to show at the molecular scale how important plant nutrients like potassium can react with the surfaces of soil clay minerals."

Siebecker and Lewis theorize that the formation of new minerals in soil occurs quickly and acts as a sink to bind tightly with potassium, far more rapidly than previously known. This new mineral formation can occur over several minutes to hours, representing a major shift in the understanding of potassium fixation.

Through their experiments, they hope to determine the extent of the reaction, the rate of the reaction and the effects of temperature on potassium adsorption, surface precipitation and desorption onto and from soil metal oxides and clay minerals. In soils, adsorption is the process where a solid holds molecules tightly onto its surface. Desorption is the release of an adsorbed substance from a surface.

Experiments will be conducted on sorption/desorption of potassium onto and from individual or mixtures of metal oxides and/or clay minerals. Quantification of the dissolved products will be determined, and solid-phase products will be characterized using detection techniques such as X-ray absorption spectroscopy and transmission electron microscopy to reach their results. The data will then be analyzed to determine the changes in potassium chemistry over time.

Siebecker said the project will help advance scientific understanding of the physical and chemical processes that impact potassium fixation and bioavailability. It also will help enhance soil health and agricultural production by improving recommendations on fertilizer application to increase nutrient efficiency.

"Soil chemical reactions impact plant nutrient bioavailability," Siebecker said. "However, a critical knowledge gap is our understanding of how soil minerals, like metal oxides, can impact that bioavailability. This work focuses on that knowledge gap by analyzing the chemical reactions that take place on soil mineral surfaces, which can tightly bind plant nutrients."