03 Apr Calcium Management in Alfalfa
Wouldn’t you adopt a technology that both increased alfalfa yield and improved quality of the forage? Learning to manage calcium should become part of your alfalfa management plan for this reason.
Alfalfa is a forage crop grown across the U.S. as high value and protein crop sought after by dairies, sheep, cattle, and horse owners. A high relative feed value (RFV) exceeding 180 to 200 makes it very sought after by commercial dairies. With proper management and fertility, yields can reach 8 to 10 tons per acre. Management is the key to high yield and high-quality alfalfa production. This includes maintaining good soil conditions and drainage while supplying the right amount of nutrients based on tonnage goals. Having an intentional management strategy like this can help increase profitability.
As a crop, alfalfa removes large quantities of nutrients from soil. Historically, phosphorus and potassium are the most important followed by calcium (Ca), magnesium (Mg) and sulfur (S).
Calcium plays a vital role in the health of all plants and animals. In cattle, horses and sheep, it helps regulate muscle movement and is a component of bones and teeth. Many producers rely on alfalfa to provide part of their animal’s Ca requirement. And only 30 to 40% of the total calcium in alfalfa is available to livestock because much of the Ca is tied up as calcium oxalate, which has a low availability.
Calcium is absorbed in relatively large amounts by alfalfa, about 30 to 40 lbs. per ton. A 6 to 8-ton crop requires 200 to 300 lbs. of available Calcium. However, due to ample soil exchange reserves, deficiencies are rare. The requirement for calcium is nearly as large as the requirement for potassium and greater than phosphorus. Calcium is a key component of cell wall structure and is important for structure and standability. Deficiency symptoms first appear as interveinal chlorosis followed by whole leaf bleaching.
Potassium (K) is routinely added as a fertilizer nutrient since alfalfa has a high requirement (up to 300 lbs. potash for a 8-ton yield). 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 followed by a decline in Ca uptake. Alfalfa will take up more K than needed for optimum growth and yield and cause a shortage of available calcium in the plant. Unfortunately, there isn’t much you can do to correct preferential K uptake. That’s why its important to make Ca more available and reusable in the plant.
If you strive for high quality alfalfa, you also must assure enough calcium is bioavailable in the plant. Only 30 to 40% of the total calcium in alfalfa is available because most is bound as calcium oxalate – an undigestible mineral. This bound calcium isn’t available for reuse in the plant or available to livestock that consume the forage. Making more calcium available in the plant and to livestock that consume should be part of an alfalfa management plan.
Modulating calcium and enabling it to be more mobile and available in plants is a key benefit of Plant Impact’s Fortalis®. Calcium, which may show sufficiency by tissue tests, isn’t always available to meet demand at sites of growth such as leaf axils, flower buds, or fruiting bodies. Since calcium could be considered immobile, alfalfa plants can’t naturally recycle it to support new growth.
Plant Impact has been testing the use of Fortalis on alfalfa to improve calcium mobility. Their preliminary testing shows that Fortalis can increase yield and perhaps digestibility by keeping calcium more available. I did a preliminary pilot study on our farm in Nebraska in 2018 and found a significant increase in bale count with the third cutting and a slight increase in bale count with the fourth cutting. However, I didn’t measure feed value or digestibility. Plant Impact is planning more conclusive testing in 2019 so stay tuned for further results.
Dan Davidson is a PhD agronomist, part-time farmer and soybean expert from Nebraska who consults with soybean checkoff and industry on crop production, marketing, and product development projects.