Potassium, also referred to as potash, is the third main element required for plant growth after nitrogen and phosphorus. Potassium is commercially produced by mining evaporite deposits deep in the earth. Potassium is a common element in feldspars, a group of rock-forming silicate minerals. Canada is one of the largest producers of potash globally, as some of the biggest potassium deposits are located in Saskatchewan.
Image courtesy: Taurus Ag
Soils naturally contain potassium in larger amounts than other macronutrients, but most of that potassium is unavailable for uptake by plants. It is recommended to get a soil test before applying any fertilizers to determine macronutrient levels in your soil. If there is a deficiency in available K, you will need to apply some additional amount of soluble K, or incorporate microorganisms that will convert unavailable K into plant available forms. How is potassium present in soil?
This diagram illustrates the quantity of potassium present in the soil in each of its different forms. Exchangeable potassium is present in the lowest quantity while Unavailable potassium (potassium lattice) is the highest quantity, but is not available for plant use. Diagram courtesy of Floodedsoils.
Potassium is usually available in soil in one of 4 forms:
Soil Solution Potassium
Unavailable Potassium can be found in the crystalline structures of feldspars and clay minerals which are incorporated into the soil structure. Very slowly over time, these minerals will break down in the soil and extremely small quantities of potassium will be released into the soil solution.
Fixed Potassium slowly becomes available to plants throughout the growing season. Clay minerals actually have the ability to fix potassium. As soil moisture levels fluctuate in the soil over the growing season, potassium will become trapped in between the mineral layers of clay. When the soil gets wet, some of the trapped ions will be released into the soil solution.
Exchangeable Potassium is readily available and easily absorbed by plants. Exchangeable potassium is found on the surface of clay particles and within organic matter in the soil. This form of potassium is easily released when plants uptake potassium from the soil solution.
Soil Solution Potassium is readily available and has already dissolved in the soil solution. This is the smallest pool of potassium available in your soil.
Potassium gives us an interesting problem as it is present in the soil, but not in forms that are available to the plant. One option for increasing potassium availability is to apply soluble potash fertilizers, though it seems redundant to be adding a nutrient that is already available in your soil. How we do expedite the decomposition of unavailable potassium?
Friends with Benefits – K-Solubilizing Microorganisms
As mentioned, potassium is often present in the soil, but in unavailable forms. How can the potassium that’s unavailable in your soil be made available to plants? Microbes! Plants have naturally evolved with beneficial microorganisms over millions of years. Soil microorganisms are responsible for maintaining the nutrient cycling process in your soil, and creating equilibrium in the soil food web. For the purpose of this article, we are going to focus on the processes used by microorganisms to make potassium available to your plants without having to apply additional, expensive chemical amendments.
Potassium Solubilization with KSBs
Recent research shows that soil microorganisms can be used to solubilize or mobilize potassium in soil and make it available for plant uptake. The microorganisms responsible for this mode of action are referred to as Potassium Solubilizing Bacteria, or KSBs. Examples of KSBs include: Bacillus muciloginosms, Bacillus circulans, and Acidothiobacillus ferrooxidans.
Image courtesy : KSM Diagram by Sattar et al. 2019
As show in the diagram above, there are several modes of actions these microbes use to remove potassium from unavailable sources and make it available for plant uptake. Essentially, KSBs can dissolve silicate minerals and release K in a plant-available form. These processes include: the production of organic and inorganic acids, chelation, exchange reactions, acidolysis, polysaccharides, and complexolysis. Additionally, KSBs and other microorganisms have a significant role in storing K in their biomass, which would be potentially available for plants. Some other microorganisms have the ability to produce other extracellular polymers and compounds that can release K from K-bearing minerals. Some microorganisms also produce a biofilm that accelerates the weathering process of rock material in the soil. Generally, the most valuable mechanisms that KSBs use to increase K availability are:
Lowering pH to dissolve silicate minerals
Enhancing chelation of cations that are bound to potassium
Acidolysis (decomposition of a mineral under the influence of an acid) of the area surrounding the microorganism
Why Use KSBs over Conventional Inputs?
Simply put, KSBs can release potassium that is already present in soil without having to purchase additional inputs, or at least significantly reduce the amount of additional potassium needed, reducing the cost per acre of potassium inputs.
For instance, by applying a smaller amount of potassium in tandem with beneficial microorganisms, the microorganisms will actually increase the efficiency of the potassium applied as the microorganisms will more quickly move potassium into the root zone of plants. Keep in mind that the microorganisms will not only be metabolizing the potassium that has been applied, but will be converting unavailable potassium in the soil into plant available forms.
Additionally, K-fertilizer prices will fluctuate with the market, potentially leaving farmers with a difficult choice of whether to fertilize or not if prices peak. Biofertilizers do not follow the same market trends and tend to be a cheaper up-front cost while providing a higher return on investment through the reduction of other inputs and increased yields.
At Nurture Growth Bio-Fertilizer, we produce a biofertilizer rich in microorganisms that can reduce the overall cost per acre of crop production. Using a patent pending proprietary blend of beneficial microorganisms, our growers have been able to reduce the quantity of conventional inputs used on site by incorporating Nurture Growth biofertilizer into their spray program.
Included in our formula are different species of bacillus, microbes capable of producing organic acids that will interact with unavailable potassium in the soil, releasing the nutrient from the soil particles it is bound by, and making that potassium available to the plant. The plant will then absorb the newly freed potassium either from the soil solution, or by directly absorbing the microbe into its roots. When applied, this microorganism will increase the amount of available potassium in soil, allowing farmers to reduce the amount of potassium inputs they are using.
We invite you to join us this year as we launch a collection of webinars about soil health, the benefits of using microorganisms, and the economic benefits of improving soil health through the use of microorganisms. Join us this month on the 17th at 10am or Mar 18 at 1pm while we discuss the importance of potassium and the role microbes play in mobilizing its availability for healthy plant growth.
Click here to view our upcoming events and register for the webinar series.
In conclusion, if you have any questions about using beneficial microorganisms, or how beneficial microorganisms can reduce your cost per acre on site, please send your inquiry to firstname.lastname@example.org and one of our team members will reach out to you promptly.
Eric is a gradate of the Environmental Science program at the University of Toronto. Coming from the green roof and landscaping industries, he does not hesitate to get his hands in the soil. He is actively searching for new ways to learn about our agricultural systems and get involved with his local agricultural community. Eric is an avid birdwatcher and advocate for environmental responsibility.