Potassium and Calcium in Alfalfa Hay
Sometimes we get so wrapped up in one aspect of management that we overlook other important aspects. For instance, calcium is an essential nutrient that generally comes from the soil and which most Montana soils have a lot of, but one seldom hears about it. Generally, almost all Montana soils have more than adequate calcium. In fact, soils often have so much calcium that it makes nutrients, such as phosphorus, unavailable.
Calcium and Livestock
Calcium plays a vital role in the health of nearly all plants and animals. In cattle and horses, its major functions include helping regulate muscle movement and acting as a chief component of bones and teeth. Many producers either produce alfalfa as a cash crop or rely on alfalfa hay to provide at least part of their animals' requirements of this necessary nutrient. Consequently, low calcium levels in hay can be a problem. Generally, only about 30 to 40% of the total calcium in alfalfa is available to livestock feeding on the alfalfa because much of the calcium is found as calcium oxalate, which has a low availability.
Calcium and Potassium
Dairy producers in Minnesota have observed low levels of calcium (Ca) in alfalfa hay in recent years. These low levels appear to be associated with high levels of potassium (K) in the soil and alfalfa tissue. This raises questions about possible management practices that might be used to increase the Ca concentration or decrease the percentage of K in the alfalfa tissue. Potassium is occasionally added as a plant nutrient, either to supply potassium, essential for straw stiffness and stem strength, or chloride, which is being looked to more and more as a deterrent of some plant diseases.
The relationship between Ca and K in plant tissue has been documented by past research. Uptake of high amounts of K can reduce the uptake of Ca. As the supply of K in soils increases, uptake of K will increase. Many plants will absorb more K than needed for optimum growth and yield. This uptake above required amounts is known as "luxury consumption."
From a crop production standpoint, there is little that can be done to reduce K uptake by plants. Obviously, it's important to avoid adding potassium to the soil system when soil test values for potassium are high. So, the first step is to routinely get a potassium soil test, especially if your forage quality tests low in calcium. The other thing to remember is that potassium is an inherent component of many soils and is constantly being released during weathering. Since potassium is generally quite mobile in the soil, it can be leached out of the soil with irrigation.The source of potassium used in a fertilizer program does not affect the K concentration in the alfalfa tissue, according to a study at the Irrigation Center in Staples in central Minnesota. The study, which compared potassium chloride, potassium sulfate, and a control, showed that both sources of potassium increased the potassium concentration in alfalfa tissue over the control, indicating that the K concentration is not affected by the source of potassium.