Annual Legumes in Fallow as an Integrated Crop/Livestock Alternative in the Central Great Plains.

Final Report for SW98-071

Project Type: Research and Education
Funds awarded in 1998: $173,979.00
Projected End Date: 12/31/2002
Matching Non-Federal Funds: $181,000.00
Region: Western
State: Wyoming
Principal Investigator:
James Krall
University of Wyoming
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Project Information


Within the region, Medicago rigidula has the greatest potential for "ley farming". It has the necessary winter survival potential, seed survival and staggered seed-softening. Annual forage pea rotated with cereals might help sustain the dryland agriculture. Austrian winter pea/sheep grazing produced more than twice the profit of wheat/fallow. Identification of pea lines for optimum winter survival has advanced to a farmer cooperator evaluation phase. Further selection should generate adapted peas of multiple market classes. No-till legume green manure increased soil carbon. With biomass additions limited by lack of moisture, no-till was critical to the storage of soil carbon and nitrogen.

Project Objectives:

1. Determine the feasibility of utilizing ley cropping systems to integrate livestock into the winter wheat-summer fallow rotation (WY).

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

3. To evaluate the economic effectiveness of incorporating alternative legume crop and livestock grazing rotations with a traditional winter wheat-fallow system (WY).

4. Demonstrate the effectiveness of incorporating legumes into the agroecosystem through on-farm research and demonstrations, field tours and media dissemination (WY, CO).


A. Background Rationale:

Most Wyoming and Colorado dryland cropping systems still include fallow, which contributes to non-sustainability. Peterson and Westfall (35) concluded that summer fallowing, as currently practiced, is having a negative impact on dryland agroecosystems. Adverse effects include decreased soil organic matter, declining soil fertility (particularly N fertility), inefficient use of the water resource, possible root zone leaching of nutrients (especially nitrate-N), the formation of saline seeps, susceptibility to both wind and water erosion, and the potential for surface and ground water pollution.

The 14-month fallow period associated with the wheat-fallow system (WF) is notoriously inefficient. Usually less than 25% of the precipitation received during fallow is stored in the soil for the subsequent wheat crop. Unfortunately, even no-till WF is still inefficient in terms of water conservation (34). Weed control with tillage leaves a bare soil surface during the latter part of the fallow period and into the wheat seedling growth period, which encourages erosion, by wind and water. Furthermore, tilled summer fallowing stimulates soil organic matter losses compared to annual cropping (22). By substituting herbicidal weed control for tillage farmers can decrease erosion, but this usually increases cost, and the net result can be less profitable than conventional tillage fallow systems (33,36). A 1996 economic review of the Great Plains concluded that more intensive crop rotations can increase returns, decrease financial risk, decrease erosion potential, and remain in compliance with 1990 Farm Bill requirements (15). Inefficient water use is a given in currently used dryland systems, which in turn can impact water quality. As much as 55 ppm nitrate has been reported in ground water beneath crop/fallow cultivated land (14). Intensifying the cropping system is the primary solution to this problem. Soil organic matter declines result in a need for supplemental N for the cereal crops. The most logical cropping system modification to add N, is a legume/cereal rotation. The legume phase of the rotation can be a grain legume, forage or green manure/cover crop. Establishing legumes on fallowed fields also offers the possibility of producing sufficient ground cover to prevent erosion during susceptible phases.
Livestock grazing on public lands is another pertinent issue. As political pressures mount, there is concern that fewer grazing acres will be available. Annual forage legumes grown on the approximately 3 million acres of annually fallowed land in Colorado and Wyoming (11) have the potential to replace much of the forage that could be lost. Diversification to a livestock/crop production enterprise also should encourage maintenance of CRP as pasture for livestock, rather than cultivation.
A 1996 review on the outlook of integrated dryland crop and livestock systems on the Great Plains reported that integrated systems are agriclimatic zone specific, and represent a potential ecologically and economically sustainable form of agriculture (27). Scientists and producers need to identify and develop appropriate integrated systems that fit the natural resource base.

B. Related and Current Work in the Area:

The Australian Ley Farming System.

In Australia, annual legume pastures integrating dryland crop and livestock production is termed "ley farming" (9,13,42,46). Medic pasture (annual species of the genus Medicago) alternates with wheat in southern Australia. Annual medics regenerate yearly from a soil seed bank, and in the pasture phase of the cycle provide forage for sheep and cattle. In the cereal phase, regenerating medics may briefly furnish forage before being eliminated by seedbed preparation and wheat planting. Medics have largely replaced fallow in the wheat production system. Today, annual medics are the principal legume component on more than 100 million acres in the "wheat-sheep" zone of southern Australia (13). Ley farming provides myriad benefits to Australian agriculture (9,42,46). The benefits include: More profitable cereal production (6); Quality livestock forage (30); Self-regenerating pastures (13,17,44); Integrated pest management (28); Reduced fertilizer inputs (18,44); Water use efficiency (10,43), Quality water (38); Quality air (38); Soil conservation (16,22); Quality soil (10,16); No strip farming (44); and Global benefit (the higher primary productivity of ley farming relative to fallow systems should result in more C fixed and less oxidation of soil organic matter). Annual legumes in rotation with cereals might similarly sustain agriculture on the U.S. Great Plains.

The West Central Great Plains (WCGP).

A limited amount of research directed at annual legumes in winter wheat/fallow systems has taken place in the WCGP. Here we briefly review our own work on four legume farming systems.

Winter Wheat - Austrian winter pea (AWP).

The potential for AWP as a green manure crop has been demonstrated in the western US (29). Beginning in 1989, 40 legume species and cultivars have been evaluated for adaptation and potential adoption as pasture in southeastern Wyoming dryland cropping systems. AWP has consistently expressed excellent potential as a green manure and forage crop in these studies. A three-year study (funded by USDA-SARE 95-034) in which peas were grown during the normal fallow period of the wheat-fallow cropping system, and were grazed by lambs, has shown agronomic and economic promise. Lamb gain averaged 0.52 (range 0.45-0.65) lbs/day with 155 lbs of gain/acre over the three years. The forage crude protein, fiber and digestibility quality traits of peas are equal to or better than alfalfa. A preliminary (three years is insufficient data in a dryland system) economic analysis indicates that the addition of peas and livestock to the traditional winter wheat - summer fallow cropping system may increase net profit 10-fold. The grazed pea crop has used only 1 additional inch (range 0-1.25) of water compared to conventional fallow. The yield of the following wheat crop was reduced 19% in 1995 and 10% in 1997 (in 1996, wheat yield was lost to hail). However, soil quality improvements with an extended period of ley farming are expected, and the negative impact on wheat yield may diminish with time.

Winter Wheat - Summer Annual Medic.

This proposed system utilizes Australian commercial cultivars of annual medic (seed of more than 30 cultivars of 10 different species are readily available). It is an out growth of a single species study established in 1995 at Archer, WY. In the establishment year the snail medic (M. scutellata cv. Sava) pasture produced 0.75 t/acre dry matter and 280 seed/ft2. The following spring approximately 4 seedlings/ft2 emerged in fallow and wheat. By mid-July the dry matter production from the medic pasture was 270 lb/acre with no medic production under wheat. A post harvest precipitation event resulted in establishment of 2.8 plants/ft2 in both pasture and stubble with dry matter production of 135 lb/acre. Limited production levels the season following sowing were expected due to the hardseededness of annual medics. It is expected that an increased proportion of softer seed in the seed bank in future years will result in markedly higher dry matter production. Variable hardseededness and its gradual breakdown ensures a supply of germinable seed in the soil seed bank at the beginning of each pasture phase. To examine environmental effect on hardseededness, a pod burial experiment was initiated in 1996 involving 10 annual medic species, at 4 depths, and to be dug up over a ten-year period.

In 1997 a time-of-sowing experiment was conducted at Archer involving 13 lines representing 10 different annual medic species. Sava was one of two lines with very short life cycles (36 days to flowering). Other species of annual medic, with longer life cycles, have a greater potential for both forage and seed yield. In 1997, 10 lines of several annual medic species were sown in a new experiment. Next year, as a component of this proposal, this experiment will be seeded to wheat, and a companion experiment will be sown to medics. Importantly, commercially-available strains of Rhizobium effectively nodulated medics.

Winter Wheat - Winter Annual Medic.

Obviously, the WCGP wheat-growing environment differs substantially from that of southern Australia. The most conspicuous difference is the colder WCGP winter temperatures. Successful growth as self-regenerating winter annual pastures in rotation with winter wheat will require levels of cold tolerance unavailable in current Australian cultivars. Fortunately, field examination of 66 potentially winter-hardy experimental lines (develop in WY) during the winters of 1996 and 1997 in southeastern Wyoming (24,26) revealed that M. rigidula and M. rigiduloides show promise as 19 of 28 lines surveyed at one or more location. Strains of Rhizobium that are effective on alfalfa in Wyoming have proven to be especially effective with M. rigidula (19). Also, foliage of the lines has remained green until early February and could provide high quality late fall and early winter forage for livestock grazing. Seed set occurred by early July which will allow two full months of true fallow prior to subsequent seeding of wheat in mid-September.

Winter Wheat - Corn - AWP.

Wheat-corn-fallow rotations have been shown to be both agronomically and economically appropriate for the WCGP (34). However, they still have a lengthy fallow period prior to the wheat crop that has inefficient water storage (31). A three-year study (funded by USDA-SARE 95-034) has been directed at growing field peas, both spring and winter types, during this fallow period, thus creating a wheat-corn-pea rotation. Peas are allowed to grow until June in the summer before wheat planting, and are then harvested for forage.

We have concluded that spring field pea (SFP) is not feasible in this rotation because stand establishment is erratic, and weak competitiveness with summer annual weeds. Austrian winter pea, however, has shown more potential, yielding 3860 lbs/A at Sterling, CO in 1996 and 3500 lbs/A at Stratton, CO in 1995. Above ground biomass N was 84 lbs/A for AWP in 1996, while root N was 40 lbs/A. If the above ground biomass were left in the field, there would be a potential for as much as 124 lbs/A of N for the subsequent crop. We believe the AWP is successful because of early spring growth which competes well with summer annual weeds. Unfortunately wheat yields in the year following the peas have been reduced by as much as 9 Bu/A compared to the no pea treatment, which was the direct result of water use by the peas. Our three years of data under dryland conditions are insufficient to draw any sound conclusions regarding: (1) economic impact, (2) water use efficiency of the whole system, (3) the N budget of the system and (4) effects on soil quality. Continued experimentation with the AWP, using the knowledge we have gained these first 3 years, is needed to determine the sustainability of the system.

In Summary.

Annual legumes form a foundation for economic sustainability in the Australian Farming system (5). Operations are diversified. Producer income is increased as soil improvement and rotational effects boost cereal crop yields, fertilizer and pesticide costs are reduced, and high-quality feed provides a basis for meat and wool production. At the same time, the system is ecologically sustainable, providing numerous benefits to natural resource conservation efforts. Preliminary research results in the WCGP indicate similar economic and ecological benefits might be realized by Wyoming and Colorado dryland agriculture if suitable annual legume systems can be developed to integrate crop and livestock production on the Great Plains. The continuation of experiments we have been conducting in the last 3 years is important. The first 2 years of data are really a function of the previous land management at each site so we are just now seeing the effects of the systems. We have launched a four-pronged attack on the problem.


Click linked name(s) to expand/collapse or show everyone's info
  • Ronald Delaney
  • Robin Groose
  • Larry Held
  • Bret Hess
  • Gary Peterson
  • Dwayne Westfall


Materials and methods:

1. Determine the feasibility of utilizing Ley cropping systems to integrate livestock into the wheat-summer fallow rotation (WY).

This was accomplished by maintaining existing and establishing two new LEY FARMING rotations with appropriate check rotations in experiments with 4 replications and identifying and developing AWP and medics adapted to the WCGP environment. A large-scale (plots ca. 1 acre) experiment had been in place for several years (funded by USDA-SARE 95-034). Both phases of the rotation (pea and wheat) were present each year. At the out set these rotations were in the third and fourth year with 2 more years remaining. In 1997, 6 summer annual medic varieties of several annual medic species were sown into 970 ft2 plots. Also, 7 winter annual lines of M rigidula and M. rigiduloides were sown in an experiment of similar design. In 1998 a companion experiment was sown to medics. Both phases of the two-year system will be present each year. We determined quantity and quality of Austrian winter pea and annual medics in these LEY FARMING systems, on the basis of both field/laboratory evaluation and livestock performance in grazing trials, especially at times when forage may be of greatest value to WCGP livestock producers (i.e., for late fall and early winter grazing).Collection of primary data on wheat yield and quality, persistence and regeneration of medic, soil water, soil quality, and weather data, together with data on forage yield and quality, provided a scientific baseline for long-term climatological and economic analysis of these Ley Farming systems.

Previously, very promising results have been obtained using seed of two commercially available cultivars of AWP (Pisum sativum ssp. arvens). However, neither of these cultivars was bred specifically for use in the Great Plains and even better results might be obtained with locally-adapted cultivars. Therefore, we established breeding nurseries to evaluate the entire U.S. National Germplasm System collection of arvens, approximately 100 lines in small plots. Promising lines were increased, and used as parents in hybridization experiments to produce even better adapted and more productive progenies. Also, we have noted some genetic variation in arvens cultivars and have a selection program to isolate the best pure-line genotypes within populations. We continued to evaluate diverse lines of M. rigidula and M. rigiduloides. Also, segregating populations derived from more that 25 intraspecific and interspecific hybridizations involving lines of these species will be advanced in our environment using the a bulk-population@ method of plant breeding. This method of breeding self-pollinated crops fully exploits natural selection for adaptation (37).

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

This was accomplished by modifying two existing experiments at Sterling and Stratton, CO and adding some new treatments involving medics. The wheat-corn- Austrian winter pea (AWP) treatments were maintained and the remaining plots that were in spring field pea were used for four new medic treatments. The most winter hardy medics, as recommended from the preliminary Wyoming research were used in the intensive rotation, creating a wheat-corn-medic system. All phases of each rotation were present each year. We maintained the AWP treatments as follows: 1) No peas; 2)100% of pea crop left on soil surface; 3) 50% of pea crop left on soil surface; and 4) 0% of pea crop left on soil surface. The two sites differ in potential evapotranspiration and are part of an existing agroecosystem network.

The following measurements were made: a) Soil water at 21 day intervals by neutron probe through the legume growth period; b) Soil nitrate and ammonium at wheat planting in 1 foot depth increments (automated analysis of KCl extracts; c) Nitrogen content of the forage using a Leco C and N analyzer; d) Legume biomass at harvest; e) Daily climatic conditions by automated weather station; f) Wheat and corn grain yields by plot combine and total biomass by quadrat sampling prior to combine harvest; g) Root mass and N content at legume harvest in the 100% remaining legume treatment. Soil was excavated to a one foot depth in a 1ft2 area and visible roots removed, washed and analyzed for total N content; h) Biologically fixed N value was calculated from the costs of the systems inputs and the value of the forage and N harvested or left in the field; and i) Soil quality evaluations (soil organic matter, structural stability, water infiltration rate, etc.) was made at the end of the 3-year project.

3. To evaluate the economic effectiveness of incorporating alternative legume crop and livestock grazing rotations with a traditional winter wheat-fallow system (WY).

The economic effectiveness of alternative farming systems was evaluated by first developing enterprise budgets, showing per unit costs and returns for alternative crop and livestock enterprises. The development of individual crop budgets used the same format and procedure used by Agee (1) for estimating costs of producing dryland wheat in Southeast Wyoming. Specifically, input and machinery costs for respective field operations was computed throughout the production cycle (considering both traditional versus new alternative crops in the rotation) with a computerized cost generator developed by Burgener and Hewlett (7). At the next stage, individual enterprise budgets were consolidated into a multi-year whole-farm simulation model to account for potential year-to-year cost and yield interrelationships, similar to a previous simulation model developed by Held and Helmers (23). In addition to evaluating each system with respect to single-point estimates of profitability, the corresponding impacts of year-to-year product price and yield variation with each respective system, was examined in the context of appropriate probability distributions with a monte carlo @RISK simulation approach. The economic analysis was completed on the pea rotations during the grant period. This analysis will also provide the framework for future evaluation of the annual medic rotations.

4, Demonstrate the effectiveness of incorporating legumes into the agroecosystem through on-farm research and demonstrations, field tours and media dissemination (WY, CO).

On-farm Research and Demonstrations.

Two sites have been established on farms in Colorado. These site were used to collect data described in objective 2. Two sites in Wyoming were established with farmers, who after recently visiting Australia, wished to examine the potential of medics (barrel, strand and snail medic cultivars) as partial fallow replacements as green manure. At each site treatments will be compared to fallow-wheat production using 4 replications and large plots. Data collection was as described in objective 1. All sites served as demonstration plots.

Methods in General.

Methodology used were of very well-established techniques for agronomic research, plant breeding, forage quality evaluation, and economic analysis. We encountered no pitfalls beyond the normal vagaries of weather involved in field research. Weather had an impact as during the period of this grant annual precipitation for the region went from near normal for 1999, to below normal in 2000, to much below normal in 2001, and 2002.

Dissemination of Results.

In addition to dissemination of our research at professional meetings, scientific journals, etc. we communicated our results to growers at field days, popular media and extension education programming.

Research results and discussion:

Milestones 1.

Medicago rigidula has the greatest potential for further development as a self-regenerating annual pasture in the dryland-cropping region of southeastern Wyoming.

After extensive evaluations of diverse annual medics (45), we determined that M. rigidula (a species found at high latitudes and elevations in Eurasia, and neither naturalized nor commercialized in Australia) is a promising candidate for winter annual regenerative pasture on the Central High Plains (40,41). This species carries the necessary winter survival potential and seed survival and staggered seed-softening for our environment (25,26,45). An especially valuable characteristic of this species is that is effectively nodulated by readily available commercial alfalfa rhizobia (19). However, establishment practices must be optimized to maximize winter survival ensure long-term pasture regeneration. Seed stocks of M. rigidula line SA10343 have increased to the point that seed is available for those interested in determining it’s region of adaptation on the Great Plains.

Milestone 2.

Annual forage pea in rotation with cereals might sustain dryland agriculture in southeastern Wyoming.

To this end researchers at the University of Wyoming have cooperated with producers to identify viable annual dryland legume cropping options. We have shown that a winter annual legume/sheep grazing agroecosystem (with Austrian winter pea, ‘AWP’; Pisum sativum ssp. arvense) might produce more than twice the profit of conventional wheat/fallow as lambs gained >0.5 lb/day grazing pea pastures and subsequent wheat crops were higher in protein compared to wheat after fallow (8,21,25). Results are promising, but more work must be done before annual legumes become prominent across the Central High Plains landscape. Now grazing studies with cattle, which are more important than sheep on the Central High Plains, are needed.

Milestone 3.

Identification of pea lines (from 80 cross-combinations) for optimum winter survival, and forage and/or grain quality and yield has advanced to a multi-site farmer cooperator evaluation phase.

F1 hybrids from 80 cross-combinations among diverse pea lines, including AWP cultivars, AWP Plant Introductions, as well as selected spring pea lines in 1999 (2,3,4,12,32,39). F2 seed was produced in the greenhouse and 17,062 seed were space-planted at Archer WY in fall 2000. 489 selected F2 plants from among 3,292 winter survivors (19% survival, with some F2 families superior to existing cultivars) were single-plant threshed at maturity in summer 2001. Currently 168 F3 lines from 52 of the 80 original cross-combinations are being advanced to the F4 generation and for further selection among and within lines. Uniform lines will be further multiplied for possible seeding (pending funding) in 5ft by 20ft plots in replicated trials on cooperators’ farms and UW-SCAREC sites and for nutritional analyses. Selected lines are either true-breeding or still segregating for various combinations of foliage traits (semi-leafless or ‘afila’, reduced stipules, leafless, acacia-type, etc.), indeterminate and semi-determinate growth habit, purple vs. white flowers (and pigmented vs. clear seedcoat), yellow vs. green cotyledon, and other economic traits (2, 12). We expect further segregation for quantitative traits such as winter-hardiness, time to maturity, and forage and seed yield. Thus, with further selection these materials should generate productive, adapted pea lines of multiple of market classes and for diverse uses on the Central High Plains.

Milestone 4.

Changes in soil C from short term (5 year) legume green manure was apparent in Colorado no-till studies.

Replacing fallow with the Austrian Winter Pea green manure crop increased soil organic carbon in the surface soil at the Sterling and Stratton sites (Table 1). Removing the pea crop as a forage resulted in the same soil C levels as fallow. Management treatment did not affect soil carbon at depths below 2.5 cm depth. It is critical to note that both the Sterling and Stratton sites had no-till management. At Archer, WY, where the systems were tilled, there was no measureable effect of cropping system on soil organic C (Table 1). There was a tendency for the continuous wheat treatment, which returns the most biomass to the soil of the systems studied, to increase soil carbon relative to the other treatments, but it was not significant at the 10% alpha level.

Management effects on total soil nitrogen were a mirror image of the effects on soil carbon but the data are not included in this report. All other chemical, physical and microbiological parameters were unaffected by management treatments at all sites.

We conclude that in our climatic region, where biomass additions are limited by lack of moisture, that no-till management is critical to the storage of soil carbon and nitrogen. We would expect that given enough years the increased soil carbon levels would translate into improvements in both physical and microbiological soil properties.

Research conclusions:

Austrian Winter Peas for Dryland Grazing With Lambs

The measurable number of acres or animals that will be impacted may both be measured in the hundreds of thousands. Today, alternative crops such as sunflowers and proso millet replace 20-25% of fallow in Wyoming. Annual legumes might exceed this level of production. An especially important animal impact of legume pastures is to reduce confined feeding. The measurable economic impact to farm and ranch families and communities is impossible to predict precisely. So far, our economic analysis of grazed AWP in place of fallow favors the replacement of fallow with a return of an extra $8/acre (21). Based on a 20-25% fallow replacement this means an additional $320,000 to $400,000/yr for the agricultural economy of southeastern Wyoming alone. Adoption of these practices in adjacent states would result in substantially larger returns.

Participation Summary

Research Outcomes

No research outcomes

Education and Outreach

Participation Summary:

Education and outreach methods and analyses:

A copy of a newspaper article published in a major Wyoming newspaper the "Casper Star Tribune" was submitted with the 1999 report. Also submitted 1999 was the proceedings paper from an invited presentation given at the SARE "Farming and Ranching for Profit, Stewardship and Community" conference in Portland, OR and an abstract from the Western Crop Science Society meeting in Powell, WY. A copy of a brochure on the Australian study tour, copies of handouts provided to growers attending conferences was provided along with an ASA abstract was submitted with the 2000 annual report. We are attaching three American Society of Agronomy, Charlotte, NC abstracts for two invited presentations at the Medic symposium, and a poster presentation. A reprint of an Agronomy Journal article on the performance of annul medics, a copy of an extension circular on grazing of Austrian winter pea that is in press, and copies of two UW-Reflections magazine articles on annul forage legumes are also attached.

Education and Outreach Outcomes

Recommendations for education and outreach:

Areas needing additional study

Areas Needing Additional Study and References

Areas Needing Additional Study

(1) Expansion of the Austrian winter pea grazing/wheat system to encompass beef production.
(2) Determine optimum medic ‘ley’ establishment practices.
(3) Identification of pea lines for optimum winter survival, and forage and/or grain quality and yield.


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