Boron Management Basics

Soils in the Great Lakes Region are naturally low in boron. Over 60% of the samples analyzed at ALGL are rated as either low or very low, which is less than 0.6 ppm. Most crops respond best at a soil test level around 1.0ppm. While boron may only make up a small percentage of crop biomass, it can have a big impact on yields when applied correctly.

Boron is critical in building cell walls. So, it is important in all growth stages, but the greatest demand for boron is early in the reproductive stages when corn is forming pollen tubes and soybeans are flowering. Foliar boron applications need to be targeted a couple of weeks ahead of entering reproduction. Early season applications may not last long enough to maximize the benefits, and late season applications are not likely to produce a response.

Managing boron availability can be challenging. Boron is taken up by plants as boric acid, H₃BO or H₂BO₃^-₃. Being an acid, boron availability is greatly reduced on alkaline soils. Also, being a negatively charged anion means that it is prone to leaching. Foliar products should be used on alkaline and/or well-drained soils.

Broadcasting dry boron fertilizer products can be effective but needs to be applied carefully. Common application rates for boron target from 0.5 to 2.5 pounds per acre and common products range from 10-15% actual boron. This means that a very small amount of product needs to be uniformly spread over a large area. Boron can very easily become toxic even with a small over-application. A simple overlap in a spread pattern has the potential to lead to toxic levels. Some crops can experience toxicity at 2-3 ppm in the soil while corn and soybeans can tolerate boron levels up to about 5 ppm. In the case of an over-application, liming the area can be an effective means to reduce the availability of the boron.

Since boron toxicity is a very real concern, it is advisable to utilize foliar and broadcast application methods. Boron should not be used in any banded applications such as in-furrow, 2x2, or sidedress. The concept of banding fertilizer is to saturate a small zone in the soil to ensure availability, but in the case of boron it could easily lead to toxicity.

Contact your regional ALGL agronomist if you have questions about boron management.