Study shows benefits of manure use
By John O’Connell
KIMBERLY, Idaho — A single application of dairy manure can significantly improve soil organic matter in farm fields, according to data from the first season of an eight-year University of Idaho study into manure use.
Furthermore, barley yields shot up under the combination of a moderate dose of manure and conventional fertilizer. As manure rates increased, however, barley tended to grow too tall and tip over at the base of the stem, called lodging.
The study by UI Extension soils specialist Amber Moore offers a rare long-term look at the effects of manure use on crops commonly grown in Magic Valley rotations. It’s funded with $85,000 per year from Idaho wheat, barley, potato, sugar beet and dairy organizations.
Miller-Coors donated Moravian 69 malt barley seed, seeking better information about how dairy manure use is affecting malt barley in Magic Valley.
“With the increase in dairies, there’s becoming a huge supply of manure. That manure has a fertilizer value that is pretty substantial. If we can learn to use that tool correctly it can be very beneficial to us,” said Kerry Bowen, chairman of Snake River Sugar Research and Seed Alliance.
In USDA research fields in Kimberly, Moore planted wheat and barley this season using conventional fertilizer in one field and varying rates of manure, plus supplemental fertilizer, in other fields. At 18 tons per acre of manure, barley yielded 150.6 bushels per acre, compared with 139.2 bushels per acre on a field with only commercial fertilizer. Yields began to decline — likely due to increased lodging — at higher applications, dipping to 132.8 bushels per acre at 54 tons of manure.
“If I were a barley grower, I would be very interested in the 18-ton rate, which is not a super low rate,” Moore said.
In wheat, supplemental manure bumped yields slightly, but there was little difference as manure rates increased.
Though she thought it might take a couple of years to detect organic matter improvements from manure, she saw a noticeable difference at every application rate this season. Down to a foot deep, soil organic matter was 1.32 percent in the field with only fertilizer, compared with 1.71 percent at 54 tons of manure per acre.
In barley, growers worry manure may raise protein levels above malters’ standards. In beets, growers fear the slow release of nitrogen from manure prolongs vegetative growth at the expense of sugar accumulation. Moore has test results pending on her barley protein levels, and in next season’s trials, she’ll plant beets and potatoes both immediately following fall manure application and a full season removed from application, with cereals between.
Shoshone grower Chris Taber has found manure is an ideal nutrient source for corn. He uses a growth inhibitor in barley following manure to limit lodging and has found manure elevates barley protein, though he’s never had a batch rejected for high protein attributed to manure.
On a few occasions, he’s planted sugar beets within a year of manure, finding it reduces his sugar levels. Two years removed from manure, however, he’s seen no ill effects on beets, and believes the improved organic matter helps sugar levels. Taber, who applies at 35-40 tons per acre, focuses his manure applications on fields with sandy soils, where organic matter is in shortest supply.