Study finds crops can tolerate much thicker layers of chaff


Capital Press

It seemed intuitive to Amber Moore when she started a three-year research project that leaving a layer of chaff and stubble would stymie sugar beet growth and reduce yields.

However, it took a much thicker layer of debris than Moore anticipated to adversely affect her experimental crop.

Moore, extension soils specialist and assistant professor with the University of Idaho, said results of the collaborative project should help growers who strip-till their beet fields understand the optimal level of debris they can leave behind.

Strip-tilling involves disturbing only the portion of soil where the seeds are planted.

In Moore's study, beets were planted in strip-tilled fields following wheat in the first year, barley in the second year and oats in the third year. Debris was baled off and returned to the fields at varying depths. She expected to see yield losses during the first two years, when fields were planted under chaff layers spread at 1, 3 and 6 tons per acre. Yields remained strong up to 7 tons per acre, however. She didn't notice any significant decline until the debris rate was about 11 tons per acre, causing yield losses of 2.5 tons per acre.

"Our recommendation is don't leave more than 9 tons per acre or anticipate potential yield losses," Moore said, adding the type of grain she followed seemed to have no impact on her beets.

Moore advised growers to remove or disperse the thick trails of chaff and stubble left in the wake of their harvesters.

"It needs to be addressed. You can't just ignore the residue trails. They are causing yield losses," Moore said.

Strip-tilling, which doesn't require soil to be physically cultivated to control weeds, became an option to sugar beet growers with the advent of Roundup Ready seed, explained Mark Duffin, executive director of the Idaho Sugar Beet Growers Association. Strip-tilling helps growers reduce fuel costs, retain soil moisture and prevent erosion, he added.

"The company is encouraging the growers to look into this and consider it," Duffin said. "Different growers are trying it and having different degrees of success with it."

Moore's research also produced surprising results regarding nitrogen application methods with strip-tilling. She found no significant difference between knifing nitrogen in to a 6-inch depth and broadcasting it from above, which Moore hypothesized would be less effective because the residue would pose a barrier.

"That nitrogen application really surprised me and I suspect that was because we had a wet spring," said Kerry Bowen, who farms in the Mini-Cassia area, adding excess water likely helped the nitrogen seep into the soil. "Everything else (with Moore's research) was right on what I expected."

Bowen strip-tills about half of his beet fields, particularly those with sandy soils where strong winds would whisk away as much as 20 percent of his crop in the past. His combine is fitted with a spreader to ensure an even distribution of stubble and he follows that up with a baler and sells the bales to the dairy industry for bedding.

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