On variable soils, Indiana farmer Eric Wappel has found precision agriculture success by varying fertilizer and seeding rates, according to a recent story in Indiana Prairie Farmer magazine.

“We use variable rate application to spread phosphorus, potassium and ag lime,” he notes. “What we put where depends upon soil sample results. Soil sampling comes first. We use hybrids, but also factor in soil types and yield goals when deciding how much to apply where.”

Rates for lime, for example, vary from a half-ton per acre to 2.5 tons per acre, largely due to variations in soils. “If we just applied two tons on the whole field, we would be overapplying lime on half of a field like that,” Eric explains. By putting inputs where they’re needed most, he believes they get their highest yields.

Variable-rate application also comes into play when applying nitrogen for corn, Wappel notes. He prepares many of his own prescriptions. Once prepared, they instruct the computer controller on board the tractor cab which rate to apply where. Here’s an example of how they use variable-rate applications to vary N rates.

“We might average 150 pounds of N per acre,” he explains. “But rates applied may vary from 100 to 200 pounds per acre.”

Varying seeding rate for corn is one of the most important things they do, thanks to the variation in their soil types, Wappel says. He writes prescriptions that vary from 20,000 to 35,000 seeds per acre for the same hybrid

“If there’s a sand hill in the field, we want to drop about 20,000 there,” he notes. Average ground typically gets 31,000 seeds per acre. Since it’s cool and wet and hard to get a stand in muck, the rate there might be 35,000 seeds per acre. On what we call good ground, we’re typically going to about 34,000 seeds per acre.”