Theses and Dissertations at Montana State University (MSU)
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Item Integrating cover crop mixtures in the northern Great Plains: an ecological assessment on crop productivity, biodiversity, and temperature and moisture conditions(Montana State University - Bozeman, College of Agriculture, 2020) DuPre, Mary Ellyn; Chairperson, Graduate Committee: Fabian D. Menalled and Tim F. SeipelCropping systems can impact crop productivity and functioning of biodiversity in the Northern Great Plains, a region heavily reliant on low diversity crop rotations and off-farm inputs, and a region predicted to experience warmer and drier climate scenarios by mid-century. In three complementary studies, I compared the impacts of cover crop mixtures and termination methods on crop productivity and three forms of the associated biodiversity (weeds, soil fungi, and ground beetles), under varying temperature and soil moisture conditions. First, I assessed the impacts of the presence (cover crops and fallow) and composition (cover crop mixtures) of cover crops, termination methods (herbicide, cattle-grazing, and haying), as a function of temperature and soil moisture conditions on crop yields, and weed communities. A 5-species, early-spring mixture generated cooler temperatures, produced more biomass, and suppressed weed biomass under warmer and drier conditions, compared to summer fallow and the 7-species, mid-spring mixture. However, lower soil moisture and subsequent reduced grain yields following the mixtures, especially under warmer and drier conditions, suggests that continuously rotating wheat with mixtures may not be the optimal method to diversify small-grain cropping systems. Second, I assessed the impacts of the presence and composition of cover crops, termination methods and temperature and soil moisture conditions on fungal communities. The early-season cover crop mixture reduced plant pathogen abundance and enhanced AM fungal richness in both the soil and subsequent wheat root crop. The enhancement of beneficial fungi and fewer plant pathogens may be a proxy to better support ecosystem services through the use of cover crop mixtures. Third, I compared ground beetle communities among cover crops treatments and termination methods. Ground beetle activity density was not impacted by termination methods and was greatest in the early-season mixture at the beginning of the growing season and in summer fallow at the end of the growing season, while the mid-season mixture peaked in the middle. Ground beetle diversity peaked in the middle and differed in community composition earlier in the growing season. These results indicate that cover crop mixtures can act as an ecological filter to ground beetle communities to better support pest regulation. Overall, these studies indicate that cover crop mixtures can support crop productivity and the associated biodiversity with changes to temperature and soil moisture, although, with agronomic and ecological trade-offs.Item Response of soil bacterial communities to cropping systems, temporal changes, and environmental conditions in the northern Great Plains(Montana State University - Bozeman, College of Agriculture, 2021) Ouverson, Laura Tindall; Chairperson, Graduate Committee: Fabian D. MenalledSoil bacterial communities are essential components of the soil ecosystem that support crop production. However, agriculture in semiarid drylands and their associated soil bacterial communities face increasingly warmer and drier conditions due to climate change. Two complementary studies were conducted to assess the response of soil bacterial communities to cropping systems, temporal changes, and soil temperature and moisture conditions in semiarid, dryland agricultural systems of the Northern Great Plains. The first study focused on soil bacterial community response to crop phase in contrasting cropping systems (chemical inputs and no-till, USDA-certified organic tilled, and USDA-certified organic sheep grazed) over a growing season. Organic grazed management supported more diverse bacterial communities than chemical no-till, though diversity in all systems decreased over the growing season. Organic grazed bacterial communities were distinct from those in the organic tilled and chemical no-till systems. An interaction between cropping system and crop phase affected community dissimilarity, indicating that overarching management systems and environmental conditions are influential on soil bacterial communities. The second study evaluated soil bacterial communities in a winter wheat - cover crop or fallow rotation. Observations were conducted in the summer fallow and two cover crop mixtures differing by species composition and phenologies, terminated by three different methods (chemical, grazing, or haying), and subjected to either induced warmer/drier or ambient soil conditions. Only the presence and composition of cover crops affected bacterial community dissimilarity, where mid-season soil bacterial communities were distinct from early season and fallow communities. Bacterial communities responded to an interaction between the presence and composition of cover crops and environmental conditions, but not termination. No treatment effects were observed in bacterial communities in 2019, which could be attributed to above average rainfall. The results of these studies suggest cover crop mixtures including species tolerant to warmer and drier conditions can foster diverse soil bacterial communities compared to fallow soils. Overall, these studies contribute to a better understanding of how soil bacterial communities respond to soil health building practices in the Northern Great Plains. Cropping systems can foster unique soil bacterial communities, but these effects may be moderated by environmental and temporal conditions.Item Long term multispecies cover crops in semi-arid Montana: soil response and aboveground biomass(Montana State University - Bozeman, College of Agriculture, 2020) D'Agati, Kristen Mary; Chairperson, Graduate Committee: Catherine A. Zabinski; Perry Miller (co-chair); Perry R. Miller, Clain A. Jones and Catherine Zabinski were co-authors of the article, 'Soil biological effects of herbicide-terminated multi-species cover crop mixes, in semi-arid Montana' which is contained within this thesis.; Catherine Zabinski, Clain A. Jones and Perry R. Miller were co-authors of the article, 'Aboveground biomass quality and quantity of long-term multispecies cover crop mixes, in the semi-arid Montana' which is contained within this thesis.; Maryse Bourgault, Perry R. Miller, Clain A. Jones and Catherine Zabinski were co-authors of the article, 'Soil biological response to spraying, grazing, or haying of long-term multispecies cover crops in semi-arid Montana' which is contained within this thesis.Low and variable annual precipitation (250-350 mm) make management strategies that conserve soil moisture imperative for wheat producers in semi-arid Montana. A wheat-fallow rotation was historically the most common dryland cropping system in semi-arid Montana, due to its ability to conserve soil water; however, summer fallow has negative environmental impacts (Campbell et al., 1991). There is interest to incorporate cover crops into a rotation as a partial replacement for summer fallow to enhance soil quality. An eight-yr study explored the effect of cover crops on biological soil properties through aboveground biomass inputs of four plant functional groups: brassica (BC), fibrous root (FR), tap root (TR), and nitrogen fixers (NF) grown as two-species mixes, six-species mixes (three functional groups), a full eight-species mix, and two controls--chemical fallow and sole pea. Cover crops grew for about 60 days, were terminated with glyphosate, then soil samples were taken nine months after termination at wheat seeding. The only difference in biological parameters based on functional group was that mycorrhizal colonization in wheat was higher following FR than BC at one site. Potentially mineralizable nitrogen (PMN) was 1.6-1.7 times higher and microbial biomass was 1.4 times higher in soils from cover crop treatments relative to fallow at one of two sites. PMN was 1.2-1.3 times higher in soils from six-species mixes than two-species mixes at both sites, and six-species mixes produced 1.4 times more biomass at one site. Nitrogen fixers had the lowest C:N ratio of the functional groups at both sites, while FR had the highest at one site. In a second study of cover crop termination, cover crops were grown about 90 days and terminated with one of three strategies: chemically, grazing, or haying. Soils were sampled nine months after termination at the time of wheat seeding. Few enzyme differences and no PMN differences or meaningful patterns were discovered among termination strategies. Minimal differences in biological parameters, even when shoot biomass was removed, may mean grazing or haying could improve net revenue without detracting from soil health. In semi-arid annual systems, water limitations may be the main concern with growing cover crops.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 Multi-species cover crops in the northern Great Plains : an ecological persepctive on biodiversity and soil health(Montana State University - Bozeman, College of Agriculture, 2016) Housman, Megan Leigh; Chairperson, Graduate Committee: Catherine A. Zabinski; Susan M. Tallman, Clain A. Jones, Perry R. Miller and Catherine Zabinski were co-authors of the article, 'Soil water, soil nitrate, and residue quanity associated with cover crop mixtures in the northern Great Plains' submitted to the journal 'Agriculture, ecosystems, and environment' which is contained within this thesis.; Susan M. Tallman, Clain A. Jones, Perry R. Miller and Catherine Zabinski were co-authors of the article, 'Multi-species cover crops: effects on soil biology after one and two rotations in the semi-arid northern Great Plains' submitted to the journal 'Soil biology and biochemistry' which is contained within this thesis.As summer fallow is replaced by cover crops, we aim to address how cover crops influence soil properties. Past studies conducted across the Northern Great Plains have investigated the short- and long- term effects of LGMs on water, nitrate, and carbon storage, soil parameters including potentially mineralizable nitrogen (PMN) and enzymatic activity, and wheat yield. Less knowledge exists regarding similar short- and especially long-term effects of CCMs in the NGP. This four-year study replicated at four sites in Montana allows us to investigate how site characteristics and annual weather patterns can influence the performance of cover crop growth and the subsequent effect on soil quality. Our research approach to building cover crop mixtures using functional group composition rather than species composition aims to make the work more broadly applicable to other regions. Other regions may utilize more adapted legume or brassica species and could still use our results to estimate their effects on soil and nitrate use throughout the soil profile or their effects on soil biological parameters.Item The effects of sheep grazing for Pisum sativum or Melilotus officinalis cover crop termination(Montana State University - Bozeman, College of Agriculture, 2016) Westbrook, Jasmine Katherine; Chairperson, Graduate Committee: Craig CarrIntegration of sheep grazing into crop rotation systems has been proposed as an alternative to conventional cover crop management techniques. However, the effectiveness of this approach and its impact on subsequent crops has not been evaluated in Montana. This study assessed the use of sheep (Ovis aries) grazing to terminate field pea (Pisum sativum) and yellow sweetclover (Melilotus officinalis) cover crops used in rotation with winter wheat. Cover crops were terminated using either rotational or continuous grazing treatments and their effects on cover crop termination, sheep live weight gains, and winter wheat emergence and yield were quantified. Sheep grazing for cover crop termination was also compared to chemical termination and mechanical tillage. In 2013, yearlings grazed the winter pea cover crop for 32 days. Sheep grazing was an effective termination method (77% dead, 1% live, 22% bare ground). Average daily gains (ADGs) did not differ between grazing treatments with sheep exhibiting ADGs of 0.181 kg day -1 for rotational (230 sheep ha -1)and 0.154 kg day -1 for continuous (57 sheep ha -1) treatments (P = 0.12). Winter wheat seedling emergence post grazing was higher under the continuous grazing treatment (P = 0.017), however winter wheat yield did not differ between treatments (P = 0.91). Results indicated grazing was a viable method for terminating a pea cover crop. In 2014, yearlings grazed the sweetclover cover crop for 40 days. Sheep grazing at stocking densities of 44 and 178 sheep ha -1 did not provide effective termination (40% dead, 34% live, 9% bare groundcover). Average daily gains did not differ between grazing treatments with sheep exhibiting ADGs of 0.177 kg day -1 for rotational and 0.172 kg day -1 for continuous treatments (p = 0.79). Termination was achieved using a second group of sheep at stocking densities of 119 and 477 sheep ha -1. Winter wheat seedling emergence did not differ between grazing treatments (p = 0.95). Winter wheat yield was lower in grazed plots than tilled and chemically terminated plots. Grazing has the potential for effective cover crop termination comparable to tillage or herbicide, but results may vary with cover crop species.Item Influence of a legume covercrop on volunteer wheat, the wheat curl mite, Aceria tosichella (K.) and wheat streak mosaic virus(Montana State University - Bozeman, College of Agriculture, 1998) Carroll, Matthew WyattItem 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 Cover crop mixtures as partial summerfallow replacement in the semi-arid northern Great Plains(Montana State University - Bozeman, College of Agriculture, 2014) Tallman, Susan Marie; Chairperson, Graduate Committee: Perry Miller; Perry R. Miller, Clain A. Jones, and Catherine A. Zabinski were co-authors of the article, 'Multi-species cover crops: effects on soil nitrate, water and wheat yield in the northern Great Plains' submitted to the journal 'Journal of soil and water conservation' which is contained within this thesis.Farmers in the semi-arid northern Great Plains are currently experimenting with multi-species cover crops, or cover crop mixtures (CCMs), as a partial summerfallow replacement and conservation practice, in response to the anecdotal claim that CCMs provide more ecosystem services than their single-species legume green manure (LGM) counterparts. This is in the absence of any published data. We conducted a 2-yr plot scale study from 2012 to 2013 at four on-farm locations in Montana to compare fallow with a pea LGM and nine CCM treatments comprised of four plant functional groups, including nitrogen fixers, fibrous roots, tap roots, and brassicas. Agronomic factors reported include cover crop biomass yield, biomass N yield, soil water and nitrate-N use, and subsequent wheat yield and quality. In addition, soil biological factors measured included; microbial respiration rate, soil enzyme activity, potentially mineralizable nitrogen, and mycorrhizal colonization. Mean cover crop biomass by site ranged from 0.4 Mg ha -1 in a record dry year, to 3.7 Mg ha -1 in a record wet year. Cover crop C:N differed between single-species Pea and an eight-species Full mix only at one site-year with 13.4 and 16.7 measured for each treatment, respectively. Soil water after cover crop treatments was less than Fallow at the time of cover crop termination at three site-years, and was strongly correlated with decreased subsequent wheat yield at three N fertility levels. Surface soils were 5 to 10 °C cooler with Pea and Full cover crops than Fallow from the time of cover crop canopy closure until six to eight weeks later. Soils following cover crops had increased microbial respiration rate at one site, however, no differences in six measured soil enzymes activities were found. Mycorrhizal colonization of wheat increased at one site from 11 to 22% following cover crops when compared with Fallow. Very few differences were observed between the pea LGM and the CCM treatments in all measured factors, indicating little advantage of CCMs over LGMs after one cover crop cycle. However, field observations indicate CCMs may have potential to provide biological pest control and this topic is recommended for further study.