Theses and Dissertations at Montana State University (MSU)
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Item Integrating crop diversity, forage crops, and targeted grazing to manage Avena fatua L.(Montana State University - Bozeman, College of Agriculture, 2021) Wong, Mei-Ling; Chairperson, Graduate Committee: Fabian D. Menalled and Tim F. Seipel (co-chair)Wild oat (Avena fatua L.) is one of the most difficult weeds to manage in spring cereal crops and causes large economic losses throughout the Northern Great Plains. The continual use of herbicides for wild oat management has selected for herbicide resistant and multiple herbicide resistant biotypes and has left no selective herbicide options for farmers in small-grain fields. To sustain crop production, this thesis aimed to develop ecologically based practices to manage wild oat populations. We evaluated the impact of spring wheat height, seeding rate, crop type, forage termination method, and tillage on wild oat tiller density, biomass, and seed production. Two studies were conducted: (1) from 2017 through 2019 in Bozeman, Montana and (2) from 2018 through 2019 in Moccasin, Montana. The first study examined the combined effect of spring wheat height and seeding rate on its competitiveness against wild oat. We found that the tall near-isogenic wheat line did not have greater wild oat suppression than the short line. Spring wheat seeded at a higher than recommended rate reduced wild oat biomass and seed production only when nitrogen fertilizer was applied. The second study assessed management practices including integrating lentil, fall and spring forage mixture, sheep grazing and tilled fallow, in addition to spring wheat height and seeding rate. Forage mixtures, sheep grazing, and tillage were the most successful tactics in suppressing wild oat growth and seed production. However, wild oat suppression was not different between spring wheat and lentil, regardless of spring wheat height and seeding rate. Our results indicate that spring wheat height was not correlated with increased suppression of wild oat. A higher seeding rate of spring wheat also did not increase wild oat suppression; we suggest that fertilization may be needed to enhance crop competitiveness. Integrating forage crops with sheep grazing has the best potential to reduce the wild oat seed bank. This information can help redesign cropping systems. However, there is a continual need to develop other integrated weed management techniques to limit wild oat growth and seed production and to reduce reliance on herbicides.Item Potential for and implications of cover cropping and grazing cover crops in wheat agroecosystems in Montana(Montana State University - Bozeman, College of Agriculture, 2017) Walker, Robert Matthew; Chairperson, Graduate Committee: Perry MillerGrowing interest in cover cropping may provide a way to recouple crop and livestock production in semiarid Montana. This two-year field study examined edaphic and agronomic implications of cool- vs warm-season cover cropping, with and without grazing, compared to the grower standard practice of chemical-fallow. After one year of cover cropping/grazing, Olsen-P and acid phosphatase activity were higher in cover cropped/grazed treatments than the fallow treatment. Potentially mineralizable Nitrogen was higher in spray-terminated cover crop treatments than graze-terminated treatments, while soil Nitrate-N was statistically lower in cover cropped/grazed treatments than in the fallow treatment. Wheat yields were not statistically different between cover cropped/grazed and the fallow treatments; however, the fallow treatment had higher wheat seed protein than cover cropped/grazed treatments. This research also utilized the Land Suitability Analysis approach to examine four exemplary Montana counties for: 1) warm-season cover crop adoption; 2) integrated crop-livestock adoption; and, 3) warm-season cover crop use as forage in an integrated crop-livestock adoption. Fergus and Fallon Co.'s both contain portions of land highly suitable for warm-season cover crop production, while all four counties have areas where integrated crop-livestock systems appear to be a logistical possibility. The conclusions taken from this research - both the agricultural field experiment and land suitability analysis - will help inform land managers across Montana's agricultural community about these emerging practices in sustainable agriculture.Item Patch dynamics in grazed arid ecosystems(Montana State University - Bozeman, College of Agriculture, 2014) Bao, Sarina; Chairperson, Graduate Committee: Lisa J. RewSpatially heterogeneous, or patchy, vegetation patterns are widely distributed in arid and semiarid ecosystems and their water-redistributing role is of great ecological interests. Studies have shown effects of rain and wind, vegetation interactions, and disturbances on patch pattern formation and dynamics. In the absence of a synthesis, I have undertaken a review to systematically understand effects of these interacting factors in patch pattern formation and dynamics for two types of spotted and banded patterns. These two patterns are widely distributed and have distinctive, yet complementary features that encompass most of the patch pattern characteristics. I found that: 1) wind is as important as rain in patch pattern formation; 2) shrubs have a facilitation effect on the surrounding vegetation via several mechanisms, and 3) grazing disturbances that include foraging, excretion, and trampling have different effects on vegetation dynamics depending on the patch type and amount of annual precipitation (e.g. wet or dry years).Item Reduced grazing impacts on vegetation communities in southern Siberian taiga(Montana State University - Bozeman, College of Agriculture, 2001) Tsagaan, TemuulenItem Characterization and comparison of soils inside and outside of grazing exclosures on Yellowstone National Park's northern winter range(Montana State University - Bozeman, College of Agriculture, 1990) Lane, John RichardItem A survey of soil properties on five ranches practicing intensive time-controlled grazing in south central Montana(Montana State University - Bozeman, College of Agriculture, 1998) Heyneman, John MelvilleItem Effects of short duration, concentrated livestock grazing on soil density(Montana State University - Bozeman, College of Agriculture, 1989) Riggle, Lex AlanItem Toward ecologically-based management : biodiversity and ecosystem functions in intensively managed agroecosystems(Montana State University - Bozeman, College of Agriculture, 2014) McKenzie, Sean Cummings; Co-chairs, Graduate Committee: Fabian D. Menalled and Kevin O'NeillConcerns 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 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 strategies. 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 system, which suggests that nurse-cropping may be an effective habitat management strategy to enhance carabid populations.Item 20th Century forest-grassland ecotone shift and effects of livestock herbivory(Montana State University - Bozeman, College of Agriculture, 2005) Sankey, Temuulen Tsagaan; Chairperson, Graduate Committee: Cliff Montagne.I studied 20th Century lower forest-grassland ecotone shift in the Centennial Valley in southwestern Montana, USA and the Darhad Valley in northern Mongolia and investigated the effects of livestock herbivory on ecotone dynamics. A total of 525 aspen (Populus tremuloides) and 1,703 Douglas-fir (Pseudotsuga menziesii) trees were cored and 10,168 seedlings were counted at five sites along the ecotone in the Centennial Valley. A total of 2,968 Siberian larch (Larix sibirica) were cored and 4,709 seedlings were counted at five ecotones in the Darhad Valley. Tree-age distribution was constructed to determine 20th Century tree establishment. Tree age and location within the ecotone were correlated to describe the process of ecotone shift into the adjacent grassland. To examine livestock herbivory effects on ecotone shift, the number of new trees was correlated with ten different levels of cattle grazing intensity during the last 60 years in the Centennial Valley and with five different grazing regimes during the last 80 years in the Darhad Valley. Three different types of ecotone shift into the adjacent grassland were documented: forest boundary shift, densification, and fairy ring establishment. No evidence of ecotone shift upslope towards the forest was found. Grazing intensity had a complex relationship with tree encroachment. Aspen and Douglas-fir tree encroachment was low at medium levels of grazing intensity, but aspen establishment was higher at low and high grazing levels and Douglas-fir establishment was higher at low grazing levels. Siberian larch tree encroachment was higher at low and high grazing intensities by sheep and cattle, but it was lower at low and medium grazing levels by goat-sheep and goatsheep- cattle mixes. My results implied that grazing can both facilitate and inhibit tree encroachment. I propose a model of grazing effects on tree encroachment that integrates both inhibition and facilitation effects of grazing disturbance. I also propose a conceptual model of lower forest-grassland ecotone shift and a conceptual model of ecotone shift and livestock herbivory effects. My models suggest that grazing can be used as a tool to maintain the equilibrium between forest and grassland vegetation and to increase or decrease forest expansion.Item Soil carbon and nitrogen and greenhouse gas emissions affected by sheep grazing under dryland cropping systems(Montana State University - Bozeman, College of Agriculture, 2012) Barsotti, Joy Lynn; Chairperson, Graduate Committee: Cliff Montagne.Sheep grazing to control weeds during fallow may influence soil C and N and greenhouse gas emissions by consuming crop residue and returning feces and urine to the soil. An experiment was conducted to evaluate the effect of sheep grazing compared to tillage and herbicide application for weed control on soil total C, total N, NH 4-N, and NO 3-N contents at the 0-120 cm depth from 2009 to 2011 and greenhouse gas (CO 2, N 2O, and CH 4) emissions from May to October, 2010 and 2011 under dryland cropping systems in western Montana. Treatments were three fallow management practices (sheep grazing [GRAZ), herbicide application [CHEM], and tillage [MECH]) and three cropping sequences (continuous alfalfa [CA], continuous spring wheat [CSW], and spring wheatpea/barley hay-fallow [W-P/B-F]). Soil samples were collected with a hydraulic probe after crop harvest and greenhouse gas samples at 3 to 14 d intervals with a static chamber. Soil total C was greater in CSW and W-P/B-F than in CA at 5-30 cm but was greater in CA and CSW than in W-P/B-F at 60-90 cm. Soil total N and NO 3-N contents were greater in CSW and W-P/B-F than in CA at 5-120 cm. Soil NH 4-N content varied with treatments and years. Soil temperature and water content at 0-15 cm were greater in CHEM with W-P/B-F and GRAZ with CA than in other treatments. Greenhouse gas fluxes peaked immediately following substantial precipitation (>12 mm) and/or N fertilization, regardless of treatments. Total CO 2 flux from May to October was greater in GRAZ with CA but N 2O flux was greater in CHEM and GRAZ with CSW than in other treatments in 2010 and 2011. Total CH 4 flux was greater in CA than in CSW and W-P/BF in 2011. Net global warming potential and greenhouse gas intensity were greater in CHEM with CSW than in other treatments. Continuous spring wheat increased soil C and N storage and available N at subsurface layers compared to other cropping sequences. Because of higher N 2O emissions and lower C sequestration rate, global warming potential and greenhouse gas intensity increased under continuous spring wheat with herbicide application for weed control.