Several farmers recently reported they didn't see a pay-off for variable-rate seeding in corn. That refers to the practice of varying seeding rates, usually according to soil types in the same pass across the field. It can be done manually, but since it's easy to forget to switch back and forth, it's usually more effective if done by inserting a prescription into a computer program powered by GPS coordinates to change seeding rate on the go.
Some say it saves seed over all. Others say it puts more population on the better ground so that it will yield more. However, some say that when it's all totaled yup, you wind up using as much seed and you can't tell a yield increase either.
Bob Nielsen, Purdue University corn Extension specialist, has generally not found an advantage for variable rate seeding. The only exception is if you have ground that is so poor and low in cation exchange capacity that the optimum yield, or highest yield possible, would be say, 130 bushels per acre. If the rest of the field is more normal soil, he would go along with writing a prescription to drop seeding rate on the soil with a low yield cap, say at 35,000 seeds per acre, and using a higher rate, like 32,000 seeds per acre, on the rest of the field. He sees no advantage for going over 32,000 seeds per acre in terms of higher yield at this time on any soil type.
Ed Vieck, Vincennes, has some of the soil type Nielsen refers to- he has 'sugar sand' or watermelon sand- it is pure sand from the surface down. Some of it is irrigated, some isn't. Even irrigated it can't perform with the better ground because of its' low water-holding capacity.
"Variable rate corn seeding has paid off for us because we have such differences in soil within the same field," he says. "In some cases it may only vary for several acres in the corner of a field that is a different type of soil. Overall, though, I believe that being able to vary the rate on corn seeding rate pays off in our situation."