Degree Day Modeling and Economic Considerations of Insects and Weeds in Sheep Grazed Alfafla, Grain, and Range Production Systems

Project Overview

Project Type: Research and Education
Funds awarded in 2011: $206,700.00
Projected End Date: 12/31/2014
Region: Western
State: Montana
Principal Investigator:
Dr. Hayes Goosey
Montana State University

Annual Reports


  • Agronomic: wheat, grass (misc. perennial), hay
  • Animals: sheep


  • Animal Production: feed/forage, grazing management, grazing - rotational, stocking rate, winter forage
  • Crop Production: conservation tillage
  • Education and Training: demonstration, extension, farmer to farmer, mentoring, networking, on-farm/ranch research, youth education
  • Farm Business Management: new enterprise development, budgets/cost and returns, value added
  • Natural Resources/Environment: habitat enhancement, wildlife
  • Pest Management: biological control, cultural control, economic threshold, integrated pest management
  • Production Systems: agroecosystems
  • Sustainable Communities: community planning, public participation, urban agriculture, urban/rural integration, employment opportunities


    Concerns about intensive, chemically-based agriculture have precipitated a call for ecologically-based practices. We investigated the ramifications of two such practices. First, we investigated targeted sheep grazing for cover-crop termination. Second, we compared the community dynamics of carabid beetles (Coleoptera:Carabidae), a group of beneficial insects in agroecosystems, among three vegetation systems in alfalfa (Medicago sativa L.) production.

    Cover-crops are grown to improve soil quality and reduce erosion. While cover-crops do not provide a direct source of revenue, integrating livestock grazing to terminate them could provide alternative revenue. We conducted a two year study of the impacts of terminating cover-crops with sheep grazing on soil quality, weed and carabid communities, and crop yield in a diversified vegetable market garden. In 2012 and 2013, we seeded a four species cover-crop that was terminated by either tractor mowing or sheep grazing following a completely randomized design. In 2013, we planted spinach, kohlrabi, and lettuce into previously grazed or mowed plots following a split-plot design. The cover-crop provided forage worth $24.00 – $44.00 ha-1 as a grazing lease. There were no differences in soil chemistry, compaction, temperature, or moisture between grazed and mowed plots. Despite temporal shifts in weed and carabid community structure, we found no differences in those communities between termination methods. Finally, cash crop yields did not differ between either strategy. Our results suggest that this practice can provide an economic benefit for producers without detrimental agronomic or ecological consequences.

    Alfalfa is the third biggest crop in Montana by gross revenue. As a perennial crop, it can allow for high populations of pest and beneficial insects. Practices that favor predatory insects could enhance biological control of pests. We conducted a two year study investigating carabid community dynamics and habitat preferences of common carabid species under three habitat management strategies: monoculture alfalfa, barely nurse-cropped alfalfa, and uncultivated refugia. Our results indicate that carabid communities vary among the three systems. Barley nurse-crop systems had greater total carabid activity-density than either of the other two systems, which suggests that nurse-cropping may be an effective habitat management strategy to enhance carabid populations.

    Agriculture in the twenty-first century must balance increased demands for food, fuel, and fiber with the need to reduce adverse environmental ramifications such as eutrophication of water bodies, decreases in biodiversity, and degradation of soil structure (Foley et al. 2005). To achieve this balance, Reganold et al. (2011) call for transformative innovations that alter the entire management regime in agroecosystems. They contend that the status quo of incremental innovations aimed at altering only a single component of the entire management regime will not suffice to achieve agronomic and ecological sustainability. Here, we have investigated two ecologically-based management practices to help bring such changes to fruition. In our first study, we investigated the agronomic and ecological effects of integrating sheep grazing for cover crop termination. In our second study, we investigated the use of nurse crops as a habitat management practice for conservation of carabid beetles. Both practices have the potential to be important components in ecologically-based management and reduce reliance on off-farm synthetic inputs.

    Integrating sheep grazing for cover-crop termination could be an economically- and agronomically-beneficial practice in horticultural vegetable production. The use of cover-crops and their termination represents an integrated, ecologically-based weed management strategy (Liebman and Gallandt 1997). We compared the effects of sheep grazing for cover-crop termination with those of mowing on soil quality, forage quality, and cover-crop termination efficacy. In addition, we tested the effects of these two cover-crop termination strategies on weed pressure and crop yield in the subsequent growing season. Sheep grazing was as effective as mowing for cover-crop termination and had no detrimental effects on soil penetration resistance, chemistry, or microclimate. Additionally, weed pressure and cash-crop yield did not differ between cover-crop termination methods. The cover-crop represents a high quality forage that could provide $24.00 – $44.00 ha-1 of direct revenue for producers as a grazing lease. Thus, the integration of sheep grazing could make the use of cover-crops more economically feasible in market vegetable gardens and not have adverse effects on agronomic conditions.

    One concern with any novel land management practice is that it could potentially alter ecological communities, which in turn, may have important consequence for ecosystem services in production systems such as pest management. Thus, we also investigated the ecological consequences of integrating sheep grazing for cover-crop termination by comparing weed and carabid beetle community structure between grazed and mowed plots. We found that despite temporal shifts in both weed and carabid beetle community structure, these ecological communities did not differ between grazed and mowed plots. Our results suggest that grazing and mowing act as similar ecological filters of both weed and carabid beetle diversity.

    Our study adds to a growing body of literature on the agronomic consequences of integrated crop-livestock systems and represents one of a very few studies on integrated crop-livestock regimes in market vegetable gardens. To our knowledge, this is the first study to investigate the impacts of integrated livestock grazing on the community dynamics of associated biodiversity in horticultural vegetable production.

    In addition to our study of integrating sheep-grazing for cover crop termination, we conducted a two year study examining the drivers of carabid community dynamics and the effects of vegetation structure on the habitat preferences of common carabid species under contrasting habitat management practices. Our results indicate that carabid communities vary among monoculture alfalfa, barley nurse-crop, and uncultivated refuge fields. Barley nurse-crop fields had greater total carabid activity-density and species richness than either of the other two system, which suggests that nurse-cropping may be an effective habitat management strategy to enhance carabid populations.

    Project objectives:

    Research Questions, Objectives and Justifications

    This research attempts to determine (1) How management practices and environmental factors act as ecological filters that determine within-field levels of biodiversity, and (2) the ramifications that those practices have for associated ecological functions, namely moisture retention, net primary production, crop production, and nutrient cycling. Specifically, my research asks three main questions: (1) Do management practices that seek to reduce off-farm synthetic inputs alter the associated biodiversity of agroecosystems, (2) Do those practices alter the ecological conditions and functions necessary for production, and (3) Does cropping diversity and stability change associated diversity?

    We conducted two complementary studies to address these questions. First, we assessed the effects of sheep grazing and mowing as methods of cover crop termination on plant and carabid beetle community structure as well as soil physical and chemical properties in small-scale cropping systems. Second, we compared the weed and carbid communities among an alfalfa (Medicago sativa L.) monoculture, an alfalfa – hay barley (Hordeum vulgare L.) polyculture and an adjacent uncultivated hayfield. We selected carabid beetles and plants as our study taxa because of their ubiquity and importance in agroecosystems. Carabid beetles and plants are useful study organisms because they represent multiple trophic levels, they have trophic interactions with each other, their populations respond differently to agronomic management practices, and they represent two important suites of associated biodiversity.

    Ecological Consequences of Integrating Sheep Grazing for Cover-Crop Termination in Small Scale Cropping Systems

    Objective 1: Assess the impact of cover-crop termination approaches in differences in soil physical and chemical properties including nutrient status, penetration resistance, temperature, and moisture.

    Justification for Objective 1: Sheep grazing may have important consequences for soil chemical and physical properties such as accelerate nutrient cycling though inputs of labile forms of nutrients in urinate or feces (Thiessen Martens and Entz 2011). Also sheep trampling may compact the soil, thus altering soil aggregation and porosity. These perturbations could, in turn, affect water infiltration and root penetration (Zhao et al. 2012). We believe it is imperative to evaluate how termination cover crops with sheep grazing versus with mowing affects soil quality because such changes could have important consequences for cash-crop growth in successive seasons.

    Objective 2: Assess differences in plant and carabid beetle community structure between grazed and mowed cover-crops.

    Justification for Objective 2: Targeted sheep grazing and mowing as methods of cover-crop termination represent distinct ecological filters. Mowing may favor one suite of species, while grazing may favor another. Carabid beetles and plants are ubiquitous and economically important in agroecosystems. Carabid beetles are considered beneficial because they are generalist predators on a variety of pestiferous arthropods (Lovei and Sunderland 1996, Sunderland 2002) and many species are seed-predators of weeds (Lee et al. 2001, Menalled et al. 2007). Understanding changes to the carabid community is especially important for ecologically-based management because such changes may have important ramifications for conservation biocontrol of pestiferous organisms. Weeds are often blamed as an impediment to production because they compete with crops for resources (Aldrich 1987). However, weeds may confer valuable ecological benefits such as habitat for pollinators (Carvalheiro et al. 2011), and enhanced nutrient cycling (Shennan 2008). Assessing the response of the plant community to the two methods of cover-crop termination will elucidate whether sheep grazing directs plant species assemblages toward more beneficial or more insidious weed species.

    Objective 3: Quantify differences in cash-crop yield in the season following cover cropping between grazed and mowed treatments.

    Justification for Objective 3: Ultimately, economic viability will determine whether producers adopt an agronomic practice. Sheep grazing may affect important factors for crop yields such as soil quality (Sulc and Tracy 2007, Bell et al. 2011, Thiessen Martens and Entz 2011) and/or the biological community. Quantifying crop yield is crucial because it is one of the most important factors determining whether integrating sheep grazing for cover crop termination is economically viable.

    Effects of Cropping Habitat Heterogeneity on Carabid Beetle Community Structure

    Objective 1: Characterize the carabid beetle community structure among different cropping systems.

    Justification for Objective 1: Crop stability and diversity are an ecological filter for associated biodiversity. Understanding how increased vegetation structure affects carabid beetle communities will help alfalfa growers choose cropping strategies that enhance ecologically-mediated pest suppression.

    Objective 2: Identify changes in vegetation structure that may influence carabid habitat selectivity.

    Justification for Objective 2: Changes in vegetation structure can alter the resources available to and the environmental condition imposed on carbid beetles. Identifying how such resources and condition change in response to altered vegetation structure may elucidate the mechanisms by which such habitat management influences carabid beetle habitat selection in alfalfa agroecosystems.

    Assisting Public Schools with Introducing Sustainable Agriculture Concepts in the Classroom

    Objective 1: Assess the knowledge gained and behavioral changes of Life Science students exposed to green house modifications and curriculum chages which incorporate sustainable produciton in to the classroom.

    Justification for Objective 1: There is an increasing disconnect between production practices and the world population as a whole. Therefore we worked with a local public school to independantly assess student knowledge and behavioral changes pre and post-exposure to greenhouse modifications.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.