Legume Cover Crops in Fallow as an Integrated Crop/Livestock Alternative in the Northern and Central Great Plains

1994 Annual Report for SW94-006

Project Type: Research and Education
Funds awarded in 1994: $160,000.00
Projected End Date: 12/31/1996
Matching Non-Federal Funds: $79,000.00
Region: Western
State: Wyoming
Principal Investigator:
James Krall
University of Wyoming

Legume Cover Crops in Fallow as an Integrated Crop/Livestock Alternative in the Northern and Central Great Plains



1. Determine the feasibility of utilizing peas as the forage component to integrate livestock into the wheat/summer fallow cropping system (Wyoming).

2. Determine the efficiencies of water-use, biomass and N-fixation when incorporating peas into the wheat/corn/summer fallow cropping system (Colorado).

3. Determine adaptation, water-use, biomass and soil nitrogen contribution of late-summer seeded legumes in the dryland spring wheat or barley/summer fallow rotations (Montana).

4. Demonstrate the effectiveness of incorporating legumes into the agroecosystem through on-farm demonstrations, workshops, field tours and mass media for producers/extension/research and Soil Conservation Services personnel.


In Wyoming, identical Austrian winter pea (AWP) rotation studies with winter wheat were started in 1994 and 1995. Wheat yield was obtained for all rotations (combinations of the two studies) in 1997. The grazed AWP/winter wheat rotation has shown rapid gains in wheat yield going from 19 percent less than the check in 1995 to 8 percent more than the fallow/wheat check in 1997. Additionally, in 1997 wheat grain protein content following grazed peas was numerically higher (1.7%) than wheat grain after fallow. In 1996, the wheat yield was lost to hail. In 1997, lambs grazed fall planted AWP for 21 days in June with a stocking rate of 11.9 lambs/acre. Average daily gain was 0.44 lbs/day. In 1998, lambs grazed fall planted AWP for 14 days in June with a stocking rate of 13.9 lambs/A. Average daily gain was 1.0 lbs/day. Forage available at the start of the grazing was 1,760 lb/A dry matter. Peas continued to grow producing 2,540 lb/A dry matter in the ungrazed exclosure. In the grazed pasture 1,097 lb/A of pea residue was left after grazing. Based on the data from these short-term rotations the net profit from the grazed AWP/winter wheat rotation is several fold greater than from the fallow/winter wheat rotations. With the exception of fallow and grazed AWP all treatments in the 1994 study succumbed to weed pressure. The weeds were the winter annuals downy brome and volunteer rye. The treatment impacted the greatest was continuous wheat. No yield was obtained from these treatments, instead plots were mowed and residue removed. It is encouraging that after three grazing cycles of AWP annual weed pressure appears to have diminished. An assessment of winter annual grassy weed populations in wheat plantings is planned for this autumn. These results must be interpreted with caution as these rotations will need to continue several more years for conclusive interpretation. Recent funding approval by USDA-SARE will allow this to happen.

Wheat-corn-fallow rotations were established at both Sterling and Stratton, Colorado in 1994. All phases of the rotation were present every year. We installed neutron access tubes in each experimental unit to keep a record of the soil water usage by the peas and the amount of water accumulated after pea harvest for the succeeding wheat crop. After corn harvest we experimented with growing peas in the fallow period after corn for cover, nitrogen (N) contribution, and livestock forage. Several scenarios were researched from 1995-1997. By 1997 we had determined that: (1) Austrian winter pea (AWP) planted no-till in the fall after corn harvest, and (2) spring field pea (SFP) and/or AWP planted no-till in the early spring following corn harvest were the most consistent alternatives. In all cases peas were allowed to grow until June, and at that point we removed differing amounts of the peas as forage.

In Montana, all plot research was finished in 1996, therefore, no new field research was initiated in 1997. However the results from Moccasin and the grain protein results from Bozeman and Rudyard were not reported last year. Grain yield at Moccasin was unaffected by the green manure treatments when compared to a fallow check. These yield results were similar to those reported from Bozeman and Rudyard. As was mentioned in the 1996 report, drought conditions during June, July and August reduced expected yields. Grain protein content was not affected by the green manure treatments at Moccasin, Bozeman, or Rudyard. These protein results are similar to those reported last year at the Conrad location. Even though research plots funded by this grant were not reviewed by producers in 1997, they were shown other annual legume research trials at Conrad and Moccasin. Acreage of pea and lentil crops for seed, hay or green manure continues to grow in Montana. Pea and lentil acreage for all uses reported to the USDA-FSA increased from 30,844 acres in 1996 to 42,827 acres in 1997. Grower demand for information has continued to increase with the increased acreage.

Economic Analysis

In Montana, costs for green manure plantings vary with the year and species and should be compared to fallow costs. Thus the number of tillage or herbicide spray operations that the green manure crop replaces is an important factor. If the green manure is planted around July 1, then two or three tillage operations needed for conventional fallow would be eliminated, saving $10 to $15/A (assuming it costs $5/A for tillage). If a late-seeded green manure planting costs around $10 to $15/A and the effects of fallow and late-seeded green manure on the next crop are similar, the amount of N fixed would be “profit.” The second crop following the green manure would be the beneficiary of the accumulated N, and its value would depend upon the price of fertilizer N (assume $0.20/lb of N; however, area N prices vary from $0.18 to $0.30/lb) and the efficiency of converting the organic N from the green manure to an available form (assume 50%). Thus N from the late-seeded green manure would be worth $4.50 to $15/A assuming green manure dry matter yields of 0.75 to 2.5 tons/A and a N content of 3 percent.

In Wyoming, based on the data from the short-term rotations, the net profit from the grazed AWP/winter wheat rotation is several fold greater than from the fallow/winter wheat rotations. Over the four years (1995-98) an average of 160 lbs/acre in total lamb gain was realized, with no bloating problems. At $0.75/lb this was a gross income of $120.32/A.

Potential Benefits

Planting legumes in mid to late season in Montana to replace summer fallow can reduce annual soil erosion losses from 4 to 6 tons/A, increase precipitation efficiency from 20 to 50 percent, prevent excessive precipitation from forming saline seep, and eventually reduce fertilizer N costs from $4 to $15/A.

In Colorado, legumes in the wheat-corn-fallow rotation would provide diversity for weed control purposes, provide extra cover during fallow, and provide a high quality forage for livestock. Unfortunately our data have shown that the Austrian Winter Pea and spring field pea are not economically feasible in this system. Wheat yields are depressed after peas and input costs for the pea crop are high.

In Wyoming, grazed Austrian Winter Pea in place of fallow also provides diversity for weed control purposes, provides extra cover during fallow, and provides a high quality forage for livestock. Net return from grazing was positive. A detailed economic analysis will be possible thanks to recent funding approval by USDA-SARE.

This summary was prepared by the project coordinator for the 1998 reporting cycle.


Gary Peterson

Colorado State Univ.
CO 80523
Grant Jackson

Montana St. Univ.
MT 59425