John Hendrickson

John Hendrickson, USDA-ARS rangeland management specialist from the Mandan, N.D. lab, talks to producers in Sidney.

SIDNEY, Mont. – Perennials have been found to reduce inputs in subsequent annual crops, along with providing many soil quality benefits.

John Hendrickson, USDA-ARS rangeland management specialist from the Mandan, N.D. laboratory, talked to eastern Montana producers about perennials during field days in Sidney.

The Mandan ARS often works with Sidney ARS on projects, especially projects that require drier soils.

Cropping systems have become more diverse, and some are adding perennials to their annual cropping systems.

“As you look at cropping systems, there has been an evolution over time going from more simpler systems to now where there is more crop diversity in systems,” Hendrickson said. “When we look at issues of soil quality, there have been some studies that show using perennials in the crop rotation may give benefits.”

When biofuels were all the rage in the U.S. in 2006, Hendrickson and other scientists set up a project with perennials that, in particular, looked at switchgrass for cellulosic biofuel.

The scientists began the project with rotations of: switchgrass only, intermediate wheatgrass only, spring wheat only, alfalfa and intermediate wheatgrass together, and alfalfa and switchgrass together.

As a check, there was a treatment of continuous annual cropping (spring wheat) that was fertilized with 60 pounds nitrogen (N).

“We had these plots set up that were 30 feet wide by 120 feet long, and we were not only interested in which of the perennial treatments would give annual crops a boost but also how long they had to be in there to provide a boost,” he said.

Every year, the ARS scientists began removing one-fourth of the plots, or 30 by 30 feet of plot area.

“That allowed us to do this project over four years,” he said. “That now only showed us which one of these systems gave the soil a boost but it also showed how long they had to be in the rotation, which turned out to provide an interesting aspect (to the project).”

Mark Liebig, USDA-ARS soil scientist in Mandan, looked at soil attributes of the project.

With his part, Liebig found that when forages were added into the annual cropping system, there were:

- Reduced acidity in the soil, along with soil bulk density.

- Improved soil aggregate stability and other soil health quality parameters.

“What I found especially interesting is we had previously thought only alfalfa would give the soil a boost,” Hendrickson said.

When the scientists added intermediate wheatgrass into the alfalfa, they discovered the soil organic carbon and soil bulk density were “given a good boost as far as our soil quality parameters.”

“Soil quality parameters are good, but is there any benefit to you as a producer?” he asked.

Hendrickson said they looked at the project as “on a fertilizer basis.”

“Each year, when we took out that 30 feet, we did not add any more fertilizer to that,” Hendrickson said. “We split it out and we put it into continuous spring wheat.”

The way the project was set up was they would look at the new continuous spring wheat rotation and compare it to the spring wheat rotation (check) that was fertilized.

“We found that if you have two years of alfalfa or three years of an alfalfa/grass mix, you would get wheat yields that were similar to the fertilized (60 pounds N) spring wheat yields,” he said.

The scientists also looked at the yield benefit of increasing rotations to four years of alfalfa or five years of an alfalfa/perennial grass mixture.

“We had spring wheat yields without N for the next four growing seasons that were similar to our fertilized spring wheat,” Hendrickson said. “The yields weren’t necessarily better, but they were similar to our fertilized spring wheat.”

The one issue with the switchgrass and the alfalfa rotation was the “alfalfa was really competitive with switchgrass.”

“We were concerned about this competition issue early, so when we originally put in this project, we seeded the intermediate wheatgrass and the switchgrass a year before we put in the alfalfa and we did it in alternate rows,” he said.

The scientists planted a row of intermediate wheatgrass and then a row of peas or switchgrass, a row of peas, the year before, and then seeded a row of peas.

The second year they filled in those alternate rows with alfalfa.

“Even doing that, the switchgrass didn’t compete well with the alfalfa over time,” Hendrickson said.

“So you need to think about that.”

Hendrickson said perennials offer many soil quality benefits in the cropping system.

But how do producers go from a perennial to an annual?

“We had another project where we looked at going from intermediate wheatgrass to an annual crop,” he said.

They compared three tillage systems, and one of those was an organic system, which was “too confusing,” so was not continued.

Hendrickson said they compared the other tillage systems, a no-till and a minimum-till system.

“With the no-till, we just sprayed out the intermediate wheatgrass and seeded into that,” he said.

With the minimum-till, they ran an undercutter under it first before seeding.

In general, yields were better with no-till than minimum-till.

“There were a few times when yields were pretty comparable, but generally, no-till was the better option,” Hendrickson said.

During the project, the scientists found that there had been some grazing on the wheatgrass ahead of time.

“We found that grazing would switch your weed populations around. So, if you do have (perennial) areas like this that you want to utilize as forage before you switch to an annual crop, you can use grazing as a way to switch it into the weed populations you may want,” he said.

How do producers transition from annuals to perennials? They set up a project looking at five annual crops.

Scientists found the previous annual crop impacted the biomass of perennials.

In addition, the impact of the previous annual crop was found to be different for cool-season perennials versus warm-season perennials.

For more information on the results of these and other studies on the benefits of perennials, contact Hendrickson at