Soil testing laboratories are asked to analyze for boron and give recommendations based on the results. The reliable response curves in the US come from the southeast, Georgia, Alabama, Florida, etc., where boron levels are low and responses are common for many crops. The critical soil test level is about 1 ppm for hot water soluble boron. Many soils in the southeastern US contain no pool of active minerals that replace boron lost to leaching and crop removal. In North Dakota, our soils are mostly derived from marine sediments.
Marine sediments are minerals that settled down through oceans, which are relatively high in boron.
As a result, our soils have a store of high boron-containing minerals not found in the southeast. So although a soil test contains less than 1 ppm boron, the number probably means a different response probability than a similar test in Georgia. North Dakota soil scientists are simply not able to predict response because none have been found here. Boron deficient soil would not be expected to achieve these yields. Boron is one nutrient where the line between adequate and too much is very thin.