Improving your crop nutrition program depends on identifying deficiencies and understanding how K interacts with other nutrients, as well as its movement within the soil and plant.
Potassium Plays Many Roles
When it comes to growing a healthy plant, K plays multiple important and different roles. Potassium is part of various chemical reactions in a plant, including photosynthesis, protein synthesis and starch synthesis:
- Photosynthesis: When K is deficient, using sunlight to synthesize foods from carbon dioxide and water, declines and respiration increases. This combination lowers the plant’s carbohydrate supply and overall crop health.
- Protein synthesis: Potassium assists in the process of bringing material to and from the areas where protein molecules are created. For example, K helps with nitrate uptake by the plant’s roots, and brings it to these areas to be turned into protein. Plants need protein to fight off diseases and for protection from harmful chemicals.
- Starch synthesis: Potassium activates the enzyme responsible for this process, in addition to many other growth enzymes. This process allows plants to produce grains rich in starch.
Potassium also helps maintain a plant’s structure (through turgor pressure) and reduces wilting. Without K, these processes cannot fully and efficiently take place within the plant, which can impact the health of the plant, leading to lower yield. It’s important to consider application rate and timing to supply adequate amounts of K to your crops.
Uptake and Availability
Potassium (K) is generally considered to be an immobile nutrient in the soil. More accurately stated, K has limited mobility in the soil, meaning that it is a bit more mobile than Phosphorus (P), but significantly less mobile than other macronutrients like Nitrogen (N) or Sulfur (S). Many soils may have a great deal of total potassium found as insoluble minerals, but only a small portion will be in soil solution or available to a crop during that growing season. Over time, mineral rock can weather and release K into the rooting zone, but rates are often too slow to meet the needs of growing crops. Recent research has started to look at clay types and content to K release rates in different soils.
Identifying soil type and texture helps determine potassium availability to the plant. Soils with higher amounts of clay content and organic matter have higher cation exchange capacity (CEC). Coarser-textured soils typically require greater amounts of K fertilizer due to low CEC. Cation exchange capacity measures the amount of positively charged cations that can be held by a given weight of soil, and affects nutrient mobility and uptake within the soil. Soils with a low CEC have a low number of positively charged ions (including K+) and have limited ability to replenish the K supply needed for crop uptake.
Soil tests that include a measurement of CEC can be beneficial to help determine soil type and the ability of the soil to retain and release nutrients to the crop.