Drought conditions across most of the high-value alfalfa acres in the United States will require closer monitoring of boron availability through the next production season.
In many states, alfalfa is the commodity crop that is most sensitive to boron deficiency. Many of those same states are facing historic drought—a combination that presents intrinsic challenges for alfalfa producers.
Alfalfa requires high inputs
Alfalfa requires high inputs, including water, to achieve high yields. The crop’s water usage ranges from 4 to 7 inches per ton of forage depending upon the environment (soil type) it’s grown in. Alfalfa’s boron susceptibility is, in part, because boron is mobile in the soil and primarily found in the organic matter of topsoil. A plant’s roots readily uptake boron in soil solution as they uptake water. When drought conditions impact water availability in topsoil, the plant is forced to rely on boron found in the subsoil, where levels are much lower. Hence, drought conditions may induce boron deficiency.
Boron deficiency symptoms
When boron deficiency is suspected, it’s important to remember that the visual effects are rarely uniform within a field. And, widespread symptoms may often be a response to drought, rather than true boron deficiency. Tissue testing throughout the growing season is paramount for the long-term success of your stand. Deficiency symptoms are most prevalent on regrowth in July and August, making the new growth in the top portion of the plant appear yellowish (which is why the condition is known as “yellow-top”).
Symptoms can also be mistaken for leafhopper damage, which also occurs late in the production season. To visually determine the cause, look for flowers on the alfalfa plant. Leafhopper damage will not prevent new growth from flowering, boron deficiency will typically prevent the plant from producing new flowers.
Diagnosing boron deficiency
Beyond a visual assessment, knowing your soils’ boron levels are adequate to meet your tonnage goals will require tissue sampling from the top 6 inches of the plant at early bloom. If boron concentration in the tissue is less than 25 ppm, a boron application will help the stand. Additionally, the roots of the crop can help diagnose plant performance issues, especially in drought-stressed crops. If a plant’s roots have restricted growth from prolonged drought stress, they will not be able to secure the water and nutrients a plant needs to flourish.
A standard soil test is also a good tool in determining the boron available to your crop. Because boron availability shifts greatly based on weather conditions, don’t rely on soil testing alone and test within a relatively close timeframe of tissue testing before making soil amendments. Boron application is needed on soil tests indicating less than 0.5 ppm boron.
Applying boron on alfalfa
Application amounts should be based on the yield goals of the stand with the results of both plant and tissue tests factored in. The following graph provides the recommended annual application rates based on tonnage removed:
Established stands should be top-dressed annually and should be split-applied, at higher concentrations, after the first and last cuttings, with other nutrients to reduce the number of passes across the stand. If no other nutrients are applied, a stand’s boron needs can be met with Solubor® sprayed on the stubble after any cutting, or in any spray application. Note: Foliar applications of boron should not exceed 0.5lb/acre/application in alfalfa.
Boron deficiency is hard on an alfalfa crop and can affect the stand’s longevity by impairing cell development. To better understand boron deficiency in alfalfa, read our Alfalfa Crop Guide. The guide offers best management practices (BMP) for fertilizer rate, timing, topdressing, and product. As always, U.S. Borax experts can answer your questions. All you have to do is contact us!