This University of Minnesota Extension blog post (Dan Kaiser, 2020) examines whether boron (B) deficiency is a problem for Minnesota crops, including corn and soybean. Boron is needed in small quantities and, since deficiencies are not widespread across the Corn Belt, data establishing reliable tissue sufficiency thresholds is lacking, making recommendations difficult to generate without an actual deficiency to calibrate against.

For corn specifically, a three-year AFREC-funded study (ending 2018) across nine irrigated and nine non-irrigated Minnesota locations broadcast boron at 3 lb/acre. Average corn grain yield was the same with or without boron at all locations. Leaf boron concentrations as low as 4 ppm at the V10 growth stage showed no yield increase, so the study could not establish a lower sufficiency threshold for tissue B in corn; the need for boron fertilization in corn was concluded to be less widespread than recent reports suggested.

For soybean and dry bean, these crops are highly sensitive to boron toxicity, so boron fertilizer application should generally be avoided. Multiple Minnesota soybean research trials found yield was not increased at most sites, and was actually decreased at a few sites. Boron toxicity symptoms have also been observed in dry bean following foliar boron application. Reports of low soybean/dry bean tissue boron from sandy soils have occurred, but there is insufficient evidence to support boron application, and tissue tests are not considered a reliable indicator of true B deficiency in these crops.

Overall recommendation: outside of sandy soils, boron deficiency is unlikely in Minnesota field crops, and growers should be cautious applying boron given toxicity risk, particularly for soybean and dry bean, where excess boron can reduce yield.