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Finding Multiple Uses for Variable-Rate Irrigation

Variable-rate irrigation (VRI) has become one of the latest solutions for conserving water and for meeting new restrictions. Nathan Weathers, who operates Weathers Family Farms near Yuma, Colorado, with his dad, Byron, has other theories on its use.    

“I can’t say we save water,” Weathers says. “However, like variable-rate fertilizer and variable-rate seeding, it allows us to put the resource where it will do the most good.”

Multipurpose Pivots

The Weathers grow nearly 3,000 acres of continuous corn that are harvested as either silage or high-moisture grain for neighboring feedlot customers. In addition to variable-rate seeding, the pair applies sidedress fertilizer at variable rates.

“That’s where we get the jump we need to meet yield goals,” Weathers explains. “We may sidedress 10 to 50 gallons per acre to match seed population and yield potential. Everything else is put on through the pivots.”

Because they rely on fertigation to spoon-feed the crop while also utilizing VRI, they have to be careful not to short it on fertilizer when there’s a change in water flow due to the extension of the corner span or a change in water application due to the prescription.

The solution is the reflex intelligent injection control system. Introduced nearly three years ago by Agri-Inject, reflex provides responsive control of fertilizer or chemical flow into an irrigation system to match changing irrigation conditions.

Weathers says the VRI prescription also corresponds with a few things learned about application during the 2012 drought. “We were working with a consultant to help us monitor our crops,” he says. “He kept telling us we were overirrigating on three pivots. I said, ‘Are you kidding me? We haven’t had rain in two months, and the leaves are curling.’

“His answer would always be, ‘Trust me,’ ” Weathers adds. “We checked with a probe, and, sure enough, the soil was so saturated, we were cutting off oxygen to the roots.”

In contrast, they have fields with sandy soil that need water regularly, even a small amount. However, too much water at once can cause fertilizer to leach through sandy soils. VRI, combined with soil moisture probes, helps solve that problem. 

“Our probes have a salt sensor that goes all the way down,” he says. “When we put fertilizer on, the salt level will spike at the shallow level, then go down as the fertilizer moves through the soil. If we see it stop between levels, we know the plant used it all. We can also tell if the fertilizer keeps going and leaches out.

“When we couple the probes and salt sensors with VRI and the reflex system, it evens it out and makes the whole system work. So far, our yields keep going up and our pounds of fertilizer per bushel keep going down,” Weathers says.

“Flow compensation lets you reduce fertilizer flow where there’s too much and lets you increase it when there’s too little,” says Josh Krautkramer of Agri-Inject. “It makes the acres and gallons of fertilizer proportional. Naturally, the fastest return will be on units with a corner span. Then, you can start working backwards to see where else it will pay.”

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