Water is also a potential source of nitrates, says Paul DeLaune, assistant professor, environmental soil science, at the Texas AgriLife Research Center at Vernon.

He discussed water quality at the Red River Crops Conference at Altus, Okla.

“Nutrients in irrigation water may offer a fertility advantage,” he says. But producers must sample irrigation water sources to determine the amount of nutrients available.

Some studies show available nitrogen levels equal to $48 per acre in nutrient savings. He also warned that nitrate concentrations in irrigation wells may be environmental issues, if allowed to get into drinking water or freshwater streams. As either resource or drawback, producers need to know if they have nitrates in their irrigation — and if they do, how much.

“As a resource, nitrates in irrigation water can be credited to crop needs,” DeLaune says. “Producers may supply a significant amount of nitrogen in the growing season through irrigation water, and it is immediately available.”

Applying 12 inches of water at 20 parts per million of nitrogen in irrigation water equals about 55 pounds per acre. Depending on the crop and other conditions, producers may reduce fertilizer application by 40 percent, just by crediting nitrate in irrigation water.

A 2011 trial showed potential to supply 100 percent of crop needs through irrigation water. “We irrigated heavily because of a season-long drought,” DeLaune says.

He breaks down the figures: Crediting from 39 pounds to 149 pounds of nitrogen per acre from well water, and using a cost of 60 cents per pound, savings would be from $23 to $89 per acre. Adding residual soil nitrate to the formula could increase available nitrogen significantly.

Determining how much residual nitrogen is available in the soil and how much is available through irrigation water offers both economic and environmental advantages, specialists say. Crediting residual nitrogen reduces the need for supplemental fertilization and reduces production costs. Reducing the amount of nitrogen applied to the soil also decreases potential for leaching into underground water and into nearby streams.

The critical factor, however, is doing the testing and then measuring the advantages of what’s already available.


More on crop management:

Managing crop nutrients through soil testing

Consider resistance in weed management strategies

Increasing wheat yield requires genetics, management