Corn and soybean take up relatively large amounts of phosphorus (P) and potassium (K), and much of this P and K ends up in the grain that is taken off the field during harvest. In order to keep soil nutrient levels from dropping over time, the amounts removed need to be replaced by applying fertilizer or manure. In order to know how much nutrient a crop removes, we need to know how much there is in a bushel of harvested grain.

We have been receiving reports since corn harvest began this fall about an unusual phenomenon: yields of the outside 8 to 24 rows on the south or west edges of corn fields show lower or much lower yields than corn farther into the field. The damage tends to be relatively uniform down or across the field, and is on field edges that border a soybean field, road, ditch, or another short-growing crop (such as forage legumes or grasses) other than corn.