Phosphorus, sulfur and zinc nutrient-uptake patterns hint at why extra fertility may pay off, says Bender, whose graduate work has focused on corn nutrient uptake. Unlike most other nutrients, phosphorus, sulfur and zinc accumulation is greater during grain-fill than during vegetative growth stages. This suggests that an assured season-long supply is critical for balanced crop nutrition and optimum grain fill, he says. In corn, half of total uptake of the three nutrients occurs after flowering. That contrasts with nitrogen, two-thirds of which is absorbed at silking.

The late-season demand for key nutrients suggests that grain yield could be lost if they are in short supply. The percentage of phosphorus, sulfur and zinc, as well as nitrogen, contained in the grain, highlights its critical nature. In the neighborhood of 60% of total nitrogen, sulfur and zinc taken up during the growing season is contained in the grain. Phosphorus tops out at 79%. In comparison, the percentage of potassium and boron in the grain is at 33% and 23%, respectively.

Among major and macronutrients, sulfur may present a special challenge. While a large percentage of most nutrients taken up by grain is mobilized from plant tissues, most sulfur in grain is taken up from the soil.