Next to nitrogen, what do you think the most important macronutrient is for corn growth? Would you have said Potassium? A study published by Purdue University and Kansas State University showed that the demand by a corn plant for nitrogen and potassium are very similar. In fact, this nitrogen-potassium balance is essential for boosting global corn yields. So how much do you actually know about potassium and its role in plant growth and development? Read along for a refresher course on potassium. Uses in plants, forms in the soil, and factors affecting uptake will all be covered.
Uses in Plants
Potassium is one of the nutrients with the most diverse application in the plant. While other nutrients have one or two specific functions, potassium is involved in a host of plant processes. In contrast with other nutrients, K is not a part of building the structure of the plant. It is a soluble ion in the plant and can easily be washed out of plant sap and returned to the soil. K is actively involved in:
· Regulation of stomatal opening, affecting amount of CO2 uptake, and conserving energy
· Used in over 60 enzymes, some that are a part of ATP formation, an energy source for the plant
· Aids in high starch grain
· Improves stalk strength and prevents lodging
· Reduces crop diseases, including stalk rots, corn leaf blight, and soybean molds and mildews
· Improves drought resistance
· Necessary for almost every part of protein synthesis
With its diversity, potassium is extremely important for plant growth and development. When deficient in potassium, symptoms can be seen in a variety of ways. In low to moderate deficiencies, a plant will experience a reduction in growth. In more severe deficiencies, foliar symptoms including yellow or burned leaf margins in soybeans, and chlorotic and burnt midribs in corn are possible. Potassium is mobile in the plant and will consequently show deficiency in the older leaves first. Potassium is taken up by plants primarily before reproductive stages, at which time it translocates K already in the plant to where it needs it. Soybeans use a particularly large amount of K and remove more in the grain than cereal crops do. Because of this, our K demand will depend on the prior crop as well as what crop will be planted.
Forms in the Soil
Potassium can be grouped into three segments in the soil.
Unavailable K is the K that is part of the mineral particles of the soil. When we consider that our very soil particles have structural components make up by K, we have an extremely large K content in our soil. However, this K is not available for plants. Over a long time, some of this K will become available for plants. However, is a very slow process and not one we can count on for a continual source of K.
Slowly available K is K that is trapped or bound between layers of clay particles. It is not readily available to plants, but will release some K into the soil each growing season often depending on the saturation of available K. The amount of K in this group depends on the amount and type of clay particles in the soil.
Readily available K is the amount of K that is available each growing season for crop uptake. This is the K that is tested when we send in soil samples and is often called exchangeable K. This K is in the soil solution or bound on the surface of clay particles. Plants will first pull K from the soil solution. The K bound on the clay particles will then release into the soil solution to recharge the levels removed by plants.
To supplement the amount of readily available K, we often apply potassium as potash or potassium chloride to provide the plants with enough K to complete all processes. Plants will uptake as much potassium as possible; they do not limit themselves to the quantity they need. This is called luxury consumption. This will not hurt the plant but will not provide any yield benefit to the plant.
Factors Affecting Plant Uptake
Soil moisture can drastically impact K availability. Dry soils result in more binding of K to clay particles and lower K availability. Wet soils increase K availability. Some sources show a greater response to K application during dry years than in wetter years.
Soil temperature can also affect availability. Colder temperatures slow down plant processes which results in slower uptake by plants as well as less movement by k off of soil particles into the soil solution.
Finally, the amount of air in the soil can also impact availability of K. Less aeration, related to poor soil structure, or saturated soils can result in less K availability.
Thresholds
There are many different sources that give different sufficiency levels for K ranging from 120 ppm to closer to 200 ppm. We’ve found over the last couple years that as we push K levels we are still able to increase yields and economic return. This is a process we are continually looking into and researching more. Are you interested in finding out some optimum K application levels on our operation? Get in contact with us and we will help you set up some field trials! Be looking out for a future blog post covering some of our results of potassium fertilization over the past 5 years.
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