Theses and Dissertations at Montana State University (MSU)
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Item Soil health response to cropping systems in semi-arid Montana(Montana State University - Bozeman, College of Agriculture, 2024) Ashford, Zane Ann; Chairperson, Graduate Committee: Catherine A. ZabinskiTraditional cropping systems in the northern Great Plains (NGP) were dominated by cereal-fallow rotations until the 1970s, resulting in increased soil erosion, decreased soil organic matter (SOM) accumulation, and declines in soil biological activity. Recent shifts toward continuous and more diverse no-till crop production attempt to increase sustainability, diversify economic opportunities, and keep up with the growing food demand without converting more land into agriculture. With a two-year study, I explored the effects of crop types in diverse, no-till, crop sequences on soil health in dryland and irrigated systems on one farm in semi-arid Montana, using biological indicators of potentially mineralizable nitrogen (PMN), soil enzyme activity (beta- glucosaminidase, beta-glucosidase, arylsulfatase, and acid and alkaline phosphatases), and permanganate oxidizable carbon (POxC), a measure of labile carbon. Crop sequences included four crop types -- cereals, oilseeds, legumes, and root crops. Root crops, namely sugar beet, drove soil responses in PMN, evident by increased plant-available N in soils following sugar beet. Soil enzyme activity, an indicator of nutrient cycling capacity, was strongly correlated with SOM, but did not follow a pattern based on crop type. Labile carbon changed in soils between years but did not respond consistently to crops. This research also explored the soil health gap by comparing soil health in cultivated systems to nearby grasslands. In a paired-site comparison on two farms in Montana, biological health indicators were 45% lower, on average, in cultivated soils compared to adjacent uncultivated soils. This difference was consistent with lower SOM averages, offering a simple assessment to quantify the maximum attainable soil health capacity within a specific agroecosystem. Soil acidification, a growing concern for producers across the NGP, contributed to 42% lower soil enzyme activity, based on four enzymes, compared to adjacent neutral pH cultivated soils. Enzyme activity was the only soil health parameter that was lower in acid soils compared to neutral pH soils, demonstrating the sensitivity of soil enzymes. Overall, these results indicate that biological soil health indicators are sensitive to changes in crop production, changing yearly, and provide farmers with the opportunity to fine- tune their management practices to meet their soil health goals.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 Soil legacy effects alter plant volatile emissions in response to diversified cropping systems(Montana State University - Bozeman, College of Agriculture, 2020) Malone, Shealyn Chelsea; Chairperson, Graduate Committee: David K. Weaver and Amy Trowbridge (co-chair); David K. Weaver, Fabian Menalled, Tim Seipel, Justin B. Runyon, Lila Hamburg, Megan L. Hofland and Amy M. Trowbridge were co-authors of the article, 'Cropping systems alter crop volatile cues important for insect pests through soil legacy effects' which is contained within this thesis.; David K. Weaver, Tim F. Seipel, Fabian D. Menalled, Megan L. Hofland, Justin B. Runyon and Amy M. Trowbridge were co-authors of the article, 'Soil microbes alter herbivore-induced volatile emissions in response to cereal cropping systems' submitted to the journal 'Plant and soil' which is contained within this thesis.Soil microbes can influence the emissions of plant volatile organic compounds (VOCs) that serve as host-location cues for insects and their natural enemies. The influence of the soil microbial community on the plasticity of plant VOC synthesis and emissions is particularly important in agricultural settings where crop rotations and management practices cause significant shifts in the soil microbiome. Studies have shown agricultural soils to influence plant-insect interactions through changes in foliar chemistry, but their potential to alter VOC emissions is unknown. To determine the effect of diversified agricultural practices on crop VOC emissions through microbe-mediated soil legacy effects, I measured VOCs from wheat (Triticum aestivum L.) in a series of field and greenhouse experiments. In Chapter II, I determined the effect of the soil microbiome on VOCs in the greenhouse by first measuring VOCs from wheat plants grown in sterilized soil or soil with added inoculum from an agricultural field. Next, to determine the effect of diversified agricultural practices on VOC phenotypes, I measured VOCs from wheat plants in the field in rotation with either fallow or a mixture of cover crops that was terminated by grazing cows. Finally, in Chapter III, I explored the interactive effect of herbivory and the soil microbiome on VOC emissions in a full factorial experiment in which wheat grown in soil inoculum from wheat-fallow or wheat-cover crop rotation that was subjected to larval feeding by the wheat stem sawfly (WSS; Cephus cinctus Norton), a major pest of wheat. Across all studies I found that soils associated with a higher microbial diversity--cover crop soils and inoculated soils--tended to emit more total VOCs and blends that would likely increase pest resistance to the WSS through 1) shifts in key bioactive compounds and 2) enhanced herbivore-induced VOC emissions. Results also suggest that soil microbes may be more likely to alter plant VOCs when plants experience abiotic or biotic stressors. Together, these results suggest that agricultural practices may indirectly influence plant resistance through microbe-altered VOCs, and these effects are more likely to occur when plants experience additional stressors, such as herbivory or drought.Item Effect of agronomic practices on disease incidence, severity, and impacts in Montana cropping systems(Montana State University - Bozeman, College of Agriculture, 2017) Ranabhat, Nar Bahadur; Chairperson, Graduate Committee: Fabian D. Menalled; Mary Burrows (co-chair)Integrated pest management is at the foundation of sustainable cropping systems. This thesis investigated 1) the influence of alternative host plants and agronomic practices on Wheat streak mosaic virus (WSMV) risk, and 2) how cover crop termination methods influence diseases in grazed organic, tilled organic, and chemical no-till systems. To assess the influence of alternative hosts including volunteer wheat, Bromus tectorum, Setaria viridis, and Zea mays on WSMV incidence and its vector, the wheat curl mite (Aceria tosichella, WCM) movement during the fall, a 'trap plant' capture system was used. In 2013, alternative hosts had similar WCM infestation levels compared to the control in most weeks. In 2014, spring planted B. tectorum and volunteer wheat increased the incidence of WSMV and abundance of WCM compared to control. In a study assessing the impact of planting date and winter wheat variety on WSMV incidence, there was almost no infection of WSMV across resistant wheat varieties. However, Pronghorn, a susceptible wheat variety, had a higher WSMV incidence at the early planting date than recommended and late planting dates. In a companion study of the impact of wheat variety and timing of N application on WSMV incidence, results did not differ across N application timing across resistant varieties. However, early spring N application in 2014 had a higher WSMV incidence compared to fall and late spring N application in Pronghorn and Yellowstone. A study assessing the impact of cropping systems on diseases indicated that disease incidence during the transition to organic period in 2013 and 2014 as well as an established organic year, 2016, was similar at tillering and flowering stages of winter wheat between the grazed organic, tilled organic, and chemical no till system. However, disease incidence was variable between systems at the matured growth stage in 2014 and 2016. In 2015, disease incidence varied between systems at all growth stages. Overall, disease severity was similar in winter wheat between grazed organic, tilled organic, and chemical no till systems, indicating disease is not a major constraint to organic methods of crop production during the transition period.Item Effects of organic and conventional cropping systems on plant diversity and plant soil feedbacks(Montana State University - Bozeman, College of Agriculture, 2015) Johnson, Stephen Patrick; Chairperson, Graduate Committee: Fabian D. Menalled; Zach J. Miller, Erik A. Lehnhoff, Perry R. Miller and Fabian D. Menalled were co-authors of the article, 'Cropping systems modify the impacts of biotic plant-soil feedbacks on wheat (Triticum aestivum L.) growth and competitive ability' submitted to the journal 'Journal of applied ecology' which is contained within this thesis.The reliance on tillage for cover crop termination, weed, and residue management is one of the biggest sustainability challenges facing organic grain farmers. Integrating grazers may be an alternative to tillage for weed management and cover crop termination. We used an on-farm trial to compare tillage-based versus grazed / reduced tillage-based management of organic crops. Our results indicate that using sheep to terminate cover crops andmanage weeds can reduce tillage intensity and provide crop yields weed communities similar to standard, tillage-intensive practices. In addition, growers leasing their land under a grazing lease may be able to increase economic returns. We also implemented a crop rotation study comparing traditional tillage-based organic to reduced-tillage organic with animal-integration, as well as to a no-till conventional system with fertilizer and pesticide inputs. There were no differences in cover crop growth and subsequent winter wheat yielded the same among the three systems. We found little evidence that weed communities differed among the three management systems in the transition to organic period. Generally, shifts in weed communities occurred across all system from one crop to the next, indicating cropping sequence structured weed communities more than divergent tillage and weed management practices Biologically-mediated plant-soil feedbacks (PSFs) are known to alter plant growth, plant-plant interactions, and plant community dynamics in natural systems. Yet, little is known about the magnitude and importance of PSFs in agro-ecosystems. Therefore, we implemented a greenhouse study that investigated the impact of organic and conventional management systems on crop growth and crop-weed interactions as mediated through PSFs. Results indicated that in general, PSFs and plant growth were more positive when soil inocula was collected from organic farms compared to conventional farms, suggesting that cropping systems modify the relative abundance of mutualistic and pathogenic organisms responsible for the observed PSFs. Also, as feedbacks became more positive, crop-weed competition decreased and facilitation increased. Therefore, in annual cropping systems, PSFs can alter plant growth and crop-weed competition.Item Nitrogen fixation by annual legume green manures in a semi-arid cropping system(Montana State University - Bozeman, College of Agriculture, 2011) McCauley, Ann Michelle; Chairperson, Graduate Committee: Clain Jones.There is renewed interest within agriculture to improve and sustain soil fertility. Legume crops can provide an alternative nitrogen (N) input to a cropping system through biological N fixation. The contribution of N from legume cropping systems depends on the quantity of N fixed and soil processes that influence soil N availability. The primary objectives of this project were 1) to evaluate the effect of planting and termination time on biomass production and N fixation by two legume green manure crops; and 2) to investigate the role of soil P availability on legume growth and N fixation. A two-yr dryland field study was conducted with three treatments: legume (field pea and lentil), planting time (spring and summer [2010 only]), and termination time (flower, intermediate [2009 only], and pod). Two methods, ¹⁵ N natural abundance and N difference, were used to quantify N fixation. In 2009, N fixed by spring-planted lentil was higher by pod than flower (P=0.03). There was no difference in N fixed by spring-planted pea among termination times, likely because of reduced precipitation during the middle of the growing season. In 2010, both spring-planted crops fixed more N by pod than flower (P<0.01) and more N was fixed by spring-planted crops than summer-planted crops (P<0.01). A greenhouse study was conducted in an unsterilized, low P soil (8 mg kg-soil -¹) with three treatments: legume crop (field pea or lentil), P fertilizer (0, 4, or 8 mg P kg -¹), and arbuscular mycorrhizae fungus (AMF) inoculum (AMF-, AMF+). Shoot biomass was sampled at flower, and N fixation was estimated with ¹⁵ N natural abundance method. Fertilization increased biomass yield and tissue N and P uptake for both crops (P<0.01) and increased N fixed by pea (P<0.01). Inoculation with AMF had little effect on measured parameters; however, there was an increase in pea biomass and N uptake in the AMF+ versus AMF- treatments at the 4P rate. Several variables that affect N fixation in semi-arid cropping systems were identified in this project, however further research assessing the effect of other soil and environmental conditions on N fixation and the cycling of fixed N in an agroecosystem is needed.Item Sustainable cropping systems for the Northern Great Plains : energetic and economic considerations(Montana State University - Bozeman, College of Agriculture, 2012) Burgess, Macdonald Hugh; Chairperson, Graduate Committee: Perry Miller.; Perry R. Miller and Clain A. Jones were co-authors of the article, 'Pulse crops improve energy intensity and productivity of cereal production in Montana, USA' in the journal 'Journal of sustainable agriculture ' which is contained within this thesis.Reliance on non-renewable resources is among the fundamental challenges to agricultural sustainability. Quantification of inputs in units of embodied fossil energy offers insight into sustainable use of these resources. Metrics of intensity, efficiency of non-renewable energy inputs to agriculture have been proposed for optimization in search of sustainability in the face of energy scarcity. Such analyses have found controversial results however, and further theoretical understanding is necessary. The research presented here focuses on approaches to sustainability targeting the semiarid northern Great Plains of North America. The 4 million ha of cropland fallowed in this region every year represent both a challenge to sustainability and an opportunity to address that challenge. Long identified as unsustainable when accomplished by tillage and without fertilizer input, the summerfallow-wheat crop production system is also energy-efficient by definitions that do not account for changes in soil fertility. It is shown here that accounting for lost soil N as an energy input to crop production partially resolves this paradox, but no strategy for energetic valuation of systems that build soil quality is apparent. Alternatives to summerfallow considered here include pulse crops (e.g. pea and lentil) grown for grain, forage, or as cover crops. In research conducted on farms already growing pulses, the largest effect on cropping system energy productivity was due to increased wheat yield rather than a reduction of inputs. In plot-scale research addressing a wider variety of production practices, neither system-level energy intensity nor productivity provided more insight into energy price exposure than basic economic analyses.Item Nitrous oxide emissions from a Northern Great Plains soil as influenced by nitrogen fertilization and cropping systems(Montana State University - Bozeman, College of Agriculture, 2006) Dusenbury, Matthew Paul; Chairperson, Graduate Committee: Richard E. Engel.Agriculture has been identified by the Intergovernmental Panel on Climate Change (IPCC) as the major anthropogenic source of N₂O emissions. Field measurements of N₂O emissions are limited for cropping systems in the semi-arid Northern Great Plains (NGP). The study objectives were to determine temporal N₂O emission patterns for NGP cropping systems, and estimate fertilizer N induced emissions (FIE) and contrast with IPCC default methodology. No-till (NT) wheat (Triticum Aestivum L.)-fallow, wheat-wheat, and wheat-pea (Pisum sativum L.), and a conventional till (CT) wheat-fallow all with three N regimes (200 and 100 kg N ha-1 available N, unfertilized N control); plus a perennial grass system (CRP) were sampled over two years (15 Apr 2004 - 14 Apr 2006) using static chambers. Nitrous oxide emissions over two years were 209 to 1310 g N ha-1 for the cropping systems. Greatest N₂O emission activity occurred following urea-N fertilization (10-wk) and freeze-thaw cycles. The sum for these periods comprised 73-84% of total emissions. Emissions were positively correlated with urea-N fertilization rates and increased rapidly when water-filled pore was > 50%.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.