Schmeeckle first tried VRI on a field that falls 45 ft. in a quarter mile, with sandy uplands and heavier-soiled lowlands. In a good year, the entire field would average around 175 bu./acre of corn, but the droughty tops rarely yielded more than 60-75 bu./acre. At the same time, over-watering was an issue in the lower half of the field, resulting in runoff and N loss, Schmeeckle says, not to mention wasted water and energy.

In 2011, Schmeeckle watered the field using a CropMetrics speed control Rx. His Valley irrigation system applied 0.60 in. water as a base rate on the majority soil type, dropped to 0.45 in. on the heavier soils and increased to 0.85 in. on the sandy ridges.

“That may not sound like a big variation,” says Shaver, the University of Nebraska scientist, “but on a 160-acre pivot over time, it adds up.” And in more arid farming regions like western Nebraska, Kansas and Texas, where irrigation is restricted, “every inch of supply is significant,” Emanuel says. “Optimizing water use helps them make the most of their water allocation.”

Schmeeckle’s field yielded 205 bu./acre last year, up 30 bu./acre from the historic average. And yields in the sandy pockets were 100 bu./acre higher than in 2009, he says. VRI “evened out yields across the whole field.”

In 2011, he used VRI management on three pivots. This year, he put another five on VRI. As the 2012 drought worsened, CropMetrics revised Schmeeckle’s watering prescriptions, narrowing the variations from the base rate.

At the end of the season, CropMetrics does a yield analysis to determine VRI benefits for each soil type and landscape position. “It takes a couple of years to fine tune the prescription,” Emanuel says.

 

Soil probe synergy

Schmeeckle combines precision watering with AquaSpy soil-water sensors, which monitor moisture and root activity in real time down to about 36 in. “The key to water-use efficiency is the soil-moisture probes plus variable rate irrigation working in conjunction,” Schmeeckle says, “because without the probes, you could still be overwatering.” Nebraska’s Shaver seconds that. “We think it’s important to use both together. The two technologies need to go hand in hand.”

In August 2011, the water sensors gave Schmeeckle confidence to turn off his pivots during a 105-degree heat wave, while his neighbors took their wells off load management and continued to water. “I could do that because I could see I had moisture at the 16-24-in. level. So I let the first 12 in. dry up and let the corn drink from the 24-in. level that week.”

 

Cost and payback

Schmeeckle pays $10/acre/year on a three-year contract for CropMetrics services, and $1,800-2,200/field/year for AquaSpy soil moisture probes and data service. His costs for pumping and pivot maintenance run $800 to $1,000/revolution. In 2011, he figures his new water management technology saved about seven pivot revolutions. In addition to water savings, VRI boosted his average 2011 corn yields by about 20 bu./acre, he says. “So I feel I’m coming out well ahead on my investment.”

In variable fields, the payback from VRI speed control can be very quick – one to three years, says Valmont’s LaRue. “But in some fields,” he cautions, “it doesn’t make