Some of you have hired lime applied variable-rate across fields for over two decades. Others also use variable-rate fertilizer applications. It helps get lime and nutrients where they should do the most good. More recently, some of you began varying seeding rates of corn and soybeans, and now a few vary nitrogen rates. If variable-rate technology works for these inputs, could it pay when the input is water applied through irrigation?

“We haven’t had any customers try it yet, but we are talking to them about it — there is interest,” says Luke Schnitker, irrigation specialist for Premier Ag Co-op. The co-op serves several counties in south-central Indiana. Variable-rate irrigation boils down to applying the right rate at the right place at the right time, he says.

The company that first introduced variable-rate irrigation is CropMetrics, a farmer-founded company located in North Bend, Neb. Nick Emanuel started CropMetrics because he wanted to share what he had learned about optimizing crop yield and minimizing input costs with others.

The idea behind variable-rate irrigation is simple, Schnitker says. For a fee, CropMetrics writes prescriptions that enable the pivot to apply more water on soils with lower water-holding capacity and less water on soils like loams, which have a higher water-holding capacity.

This concept was developed out of necessity in the West, where water is harder to come by, but it can be used here to cut input costs, optimize yields or both.

Variable-rate irrigation also can be used to even out application on "windshield wiper" pivot systems, Schnitker observes. These are irrigation systems that can’t complete a full circle due to an obstacle. Instead, they apply water out to where the pivot must reverse and then typically apply on the way back, as well.

Here’s an example from CropMetrics, Schnitker says. Instead of applying a full rate in one pass with a windshield wiper-style pivot, or applying a half rate out and a half rate back, you can start out at a quarter rate, program it to apply at a half rate through the middle part of the field, and then reverse the percentages when the pivot heads back the other way. Apply a quarter over the first part, then half, then three-quarters. All parts of the field receive the same amount of water, there’s less chance of getting the pivot stuck, and various areas of the field are treated more evenly with water.