Sheep Grazing as an Agro-Ecological Pest Management Tactic in a Minimum Till Rotational Cropping System: Biological, Ecological, and Economics Considerations

Non-Technical Summary: In 2002, 15.5 million acres of farmland in the 15 western states were rotated into summer fallow with up to 4 applications of herbicides annually for weed control. As zero tillage practices become more common, herbicide use will continue to increase. Currently, mechanical tillage is the only practical alternative to chemical fallow. However, tillage decreases residue cover, resulting in increased soil erosion. Strategic grazing of grain stubble and weeds by sheep offers an alternative to traditional stubble and weed management, and no-till biomass reduction for seed bed preparation with the added benefit of not negatively influencing soil nutrient cycling or increasing erosion potential. In addition, sheep grazing summer fallow may significantly reduce use and thus selection pressure for glyphosate resistant weeds by precluding the need to control weeds with glyphosate. Our goal is the profitable incorporation of sheep into grain production systems to reduce pesticide and fossil fuel use in fallow and stubble management. Our objectives are: 1: Compare two crop systems and three management systems (in 3 year rotation only) on: a) Grain and forage production b) weed composition, c) Population dynamics of two problematic weed species, d) Nitrogen cycling, e) Abundances and diversity of pest and beneficial insects associated with different crops, bordering crops(annual, perennial, and fallow), and fallow treatments, g) Abundances and activities of pollinators associated with alfalfa and flowering weeds. The crop rotations are 1) Continuous spring wheat - long term project control. 2) Three year rotation, spring wheat - spring planted forage pea/hay barley intercrop- summer fallow in a three year rotation with each component present every year. Within the three year rotation the management systems are: 1) No-till with sheep grazing to manage summer fallow, crop residues, and to harvest the forage crop; 2) Minimum tillage with herbicides use to manage summer fallow, forage crop harvest for hay production, and tillage for seed bed preparation; 3) Conventional Tillage used to manage summer fallow, forage crop harvest for hay production, and tillage used for seed bed preparation. 2: Using production, input data, and peer reviewed published results to compare profitability and cash flow of our two crop systems and three management systems. 3: Conduct `on campus' field demonstrations and cooperate with local high school to include student field and lab work in sustainable ag in the biological sciences. Publish and communicate results and potential economic and biological advantages of incorporating sheep grazing of stubble and weeds into a sustainable grain farming system. Our interdisciplinary team of scientists anticipates a positive long term biological and economical outcome from the integrated system of weed management by sheep grazing, and significant reduction in herbicide use in the Northern Great Plains. The proposed system encourages profitable cooperation between diverse agricultural enterprises by linking a source of inexpensive feed for sheep producers with a successful pest control method for grain farmers. <P> Approach: The study site consists of 45, 0.5-acre plots in a grain production system that are highly visible at Montana State University's Fort Ellis research facility 6 miles from Bozeman. Fallow-spring wheat, fallow-winter wheat, and continuous spring wheat, cropping systems have been in place since 2004 and ended in the fall of 2008. Plots that had been summer fallowed using tillage, herbicides, and grazing will maintain the same fallow treatment (in the 3 year rotation) into the proposed study. The continuous spring wheat "control" treatment will be maintained from the previous project. Broadleaf weed control within all cereals will be done post-emergence with appropriate herbicides such as bromoxynil + MCPA (Bronate Advanced) at 1.5 pt/acre. Summer fallow weed control in the Tillage treatment will be done solely by mechanical means. Summer fallow weed control in the minimum tillage with herbicide treatment will be done with tank-mixed glyphosate and dicamba or glyphosate alone, depending on weed species present. In the minimum tillage with herbicide and tillage fallow treatments, pea/barley forage will be harvested in late June for hay production followed by the appropriate late summer fallow treatment. In the no-till with sheep grazed summer fallow treatment, sheep will graze the pea/barley forage starting in June. In the no-till with sheep grazed summer fallow treatment, an appropriate number of sheep at the proper duration and intensity (based on the weed biomass) will be used on each grazed plot. Based upon previous research (Snyder et al., 2007) we anticipate approximately 5 sheep for each 0.5 acre summer fallow plot for 7 to 10 days. We estimate that the stocking rate will double for the pea/barley forage grazing. To achieve the desired weed removal and retain sufficient residual cover, a variable stocking rate, intensity and duration, will be employed for each plot based upon weed and volunteer availability. In previous fieldwork, we have observed that green weeds are the first plant materials consumed by sheep. Therefore, we are certain that we will be able to maintain the appropriate amount of stubble cover to conform to USDA-NRCS soil cover regulations for erosion prevention and Farm Program participation