Nebraska cover-crop trials test irrigation and nitrogen savings

By Nathan Brooks

Two cover-crop trials drilled in November at the University of Nebraska-Lincoln’s West Central Research, Extension and Education Center near North Platte are testing whether cover crops can cut irrigation, retain applied nitrogen and make financial sense for Nebraska farms.

The first-year study, funded by a North Central Sustainable Ag Research and Education grant, compares a monocrop of rye with a mix of five species. Rye established the quickest. That is an establishment observation from an active trial, not a harvested yield, final water-saving result or profitability finding.

Research lead Abia Katimbo, a UNL irrigation management specialist, is examining Nebraska’s water-quality and water-quantity problems. He said growers in western Nebraska have encountered pumping shortages in some areas, based on how much they could previously apply to fields.

The need extends beyond Nebraska. Farmers across the country are trying to produce with less as groundwater supplies decline and input prices rise.

What does cover cropping change for farm margins?

Katimbo framed the test in three parts: irrigation, nitrogen and economics. “Can the cover crop reduce irrigation and nitrogen requirements, but also do the economics make sense?” he asked.

Farmers also want to know whether cover crops fit their systems, reduce water demand or add to it, and save fertilizer or require more nitrogen. Katimbo said most research suggests cover crops can trap off-season precipitation for use in spring.

The economics remain unresolved. No measured cost or return figure has emerged from the first-year project. Any reduction in irrigation or fertilizer expense would need to offset the cost of adopting another crop practice, and the trial has not yet supplied those figures.

In western Nebraska, where some growers have already pumped less than in previous seasons, retaining more precipitation could affect how much irrigation their cash crops receive.

Can delayed termination hold more water?

Katimbo’s team is testing when to terminate the cover crop because the date affects how much water the soil reserves for the cash crop. One stand was terminated one week before planting and another one week after planting.

The after-planting termination produced more biomass. Soil-moisture probes also showed more water stored in the soil when termination came one week after planting.

Those are preliminary field-condition readings in an ongoing trial, not final harvested results. Katimbo said biomass is the deciding factor: without enough growth, a cover crop cannot capture all available water and nitrogen. The team will continue monitoring the water requirements of the fields as the trial advances.

Will cover crops keep nitrogen out of groundwater?

The researchers also are testing whether cover crops capture excess nitrogen applied to fields. If cover crops use residual fertilizer, less nitrogen should enter the groundwater supply.

The study addresses concern about nitrates in drinking-water wells. Katimbo said high nitrate levels in well water have shown a correlation with increasing cancer cases.

What role does irrigation technology play?

Katimbo runs the N-Mobile Irrigation Testing Lab, an outreach program that works with producers to improve irrigation efficiency through technology. It helps estimate crop water use at different growth stages and supports decisions about when and how much to irrigate, including before crops become stressed.

“You don’t only have to grow the cover crop; you need to have the technology that can give you an estimate of how much the crop is using at different growth stages,” Katimbo said. “Farmers need to make decisions based on data.”

The program also examines whether integrating water-saving technology into a farming operation makes economic sense. Katimbo argues that extending the life of aquifers requires regenerative practices such as cover crops, paired with technology showing how much water crops actually need.

Growers should not treat the trial as proof that a rye or mixed cover can replace irrigation or fertilizer. What the year-one work changes is the decision framework: producers can pair cover-crop and termination choices with soil-moisture measurements and crop-specific water-use estimates. As the trial progresses, the team will keep testing whether later termination, greater biomass and better irrigation data can conserve water, retain nitrogen and pay for themselves.