Tim Schmeeckle is learning to grow corn with less water. Precision-irrigation management is helping him and other farmers apply the right amount of water on every part of the field. Variable-rate irrigation (VRI) adjusts water application depth for differences in soil water-holding capacity, topography and yield potential. The goal is to boost crop production while conserving an expensive and increasingly scarce resource. “Even in a drought year,” Schmeeckle says, “I’m conserving water.”

Schmeeckle grows corn and soybeans on 2,000 irrigated acres near Gothenburg, Neb., in the Platte River Valley. He runs 11 center pivots, pumping water from the Ogallala Aquifer. “Water is our main yield-limiting factor,” says Schmeeckle, whose operation is three-quarters corn. He has no watering restrictions now, but he’s convinced that water allocations are on the way. “It’s not if, but when. I want to know how to raise the same amount of corn with less water.”

Interest in variable-rate irrigation is booming, says Tim Shaver, a soil scientist at the University of Nebraska West Central Extension and Research Center in North Platte. “We’re seeing big potential benefits in semi-arid regions where a lot of growers have water allocations. We think it’s a real promising technology.”

 

Mapping field variations

In 2011, Schmeeckle began working with CropMetrics, a variable-rate irrigation management company founded by North Bend, Neb., farmer Nick Emanuel.

The first step in VRI is mapping field variations. Variable fields offer the most opportunity for improving irrigation management, Emanuel says. “Try it first on your toughest field with the most soil variability, sandy ridges or waterlogged depressions.”

Many of Tim Schmeeckle’s fields vary in both topography and soil texture, ranging from fine sand soils, which can hold about 1 in./ft. of water, to heavier sandy loam and sandy clay loam soils, which can hold 1.4-2 in./ft. water. In fields such as these, “if you water the sandy soils right, you may flood out the better soils,” says Jake LaRue, research and development director for Valmont, maker of Valley Irrigation equipment. “But if you water the better soils right, the sandy soils dry up. So uniform application is not the answer.”

Using RTK elevation data and soil electromagnetic conductivity surveys of Schmeeckle’s fields, CropMetrics created a map of soil water-holding capacity and areas prone to runoff or waterlogging. This data was combined with aerial imagery and yield maps to generate a watering prescription, which was uploaded wirelessly to Schmeeckle’s Valley Pro2 control panel. Once the Rx is loaded, VRI is automatic, Schmeeckle adds – no babysitting required.

As the pivot rotates, the controller adjusts the base walk speed every few degrees. Water flow remains constant, while application depth increases or decreases with walk speed. On heavier soils or low spots prone to ponding, the pivot travels faster, applying less water. On lighter soils or droughty ridges, the pivot slows down, applying more water.

Each center pivot irrigation circle can be sliced into as many as 180 pie-shaped prescriptions. VRI speed control is “a low-cost way to match irrigation application depth to soil type,” Emanuel says. The software works with any electric-drive center pivot that has position-based speed control. Older pivots can be upgraded with GPS and wireless telemetry for $1,500-2,500, LaRue adds.