According to the U.S. Drought Monitor at the University of Nebraska-Lincoln’s National Drought Mitigation Center, many alfalfa-growing states are facing abnormally dry or drought conditions.1 Unfortunately, alfalfa has a high water use rate. The crop’s water usage ranges from 4 to 7 inches per ton of forage depending upon the environment it’s grown in.2
How draught can cause boron deficiency
Alfalfa is the commodity crop that is most sensitive to boron deficiency. Its 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.
Spotting boron deficiency in alfalfa
If you suspect boron deficiency, remember that the visual effects are rarely uniform within a field and may look like other conditions. Or, widespread symptoms could be a response to drought, rather than true boron deficiency.
Boron deficiency symptoms are most prevalent on regrowth in July and August, making the new growth in the top portion of the plant appear yellowish—a condition known as “yellow-top.”
Or, your stand could look like you have 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 soil’s boron levels throughout the growing season will help you determine the cause of the symptoms. There are two ways to go about this:
Tissue testing
A tissue test requires 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.
Soil testing
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. Test your soil 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.
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. As always, U.S. Borax experts can answer your questions. All you have to do is contact us!
References
1U.S. Drought Monitor. National Drought Mitigation Center: University of Nebraska-Lincoln; June 2026.
2Goplen, J and Sheaffer, C. 2024. Alfalfa during drought. University of Minnesota Extension.
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