Whenever we consider implementing a new fertilizing practice or replacing an old practice, it is important to think about why we have been using the old practice and whether or not we should expect the new practice to be a benefit under our conditions.   

You may have read recently about some work out of the University of Missouri showing that supplemental boron could improve the root development of alfalfa in an acid soil that had a high level of exchangeable aluminum. The level of aluminum was presumed to be high enough to be toxic and prevent normal root development. Addition of boron was associated with increased root growth and the assumption was that the boron may somehow prevent or alleviate the toxic effects of aluminum.   

Aluminum toxicity should never be a yield limiting factor in alfalfa production. Alfalfa fields need to have a soil pH of 6.2 or higher to maintain an environment rich in bases (like calcium, magnesium and potassium). These are required by symbiotic bacteria that make atmospheric nitrogen available to alfalfa. Since aluminum is not present in toxic concentrations until the soil pH is less than 5.5, alfalfa yield would be low in acid soils because of the nitrogen deficiency caused by inefficient symbiotic bacteria. Adding boron will not raise the soil pH as lime does, and it will not improve the available levels of calcium, magnesium and potassium. So adding boron will not improve yields.   

Boron may increase alfalfa yields if a soil boron deficiency exists. This can easily be determined by collecting surface (0 - 6") and subsurface (7 - 24") soil samples for boron soil tests. To date we have been unable to find a confirmed boron deficiency in an Oklahoma alfalfa field. If you hear of one or believe you have a boron deficiency, please let us know because we would like to have the opportunity to put out a boron fertilizer study.