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Item Investigating the impacts of agricultural land use change on regional climate processes in the northern North American Great Plains(Montana State University - Bozeman, College of Agriculture, 2021) Bromley, Gabriel Trees; Chairperson, Graduate Committee: Paul C. Stoy; Jack Brookshire (co-chair); Tobias Gerken, Andreas F. Prein and Paul C. Stoy were co-authors of the article, 'Recent trends in the near-surface climatology of the northern North American Great Plains' in the journal 'Journal of climate' which is contained within this dissertation.; Andreas F. Prein, Shannon Albeke and Paul C. Stoy were co-authors of the article, 'Simulating the impacts of agricultural land use change on the climate of the northern North American Great Plains: validating a convection-permitting climate model' submitted to the journal 'Climate dynamics' which is contained within this dissertation.; Andreas F. Prein, Shannon Albeke and Paul C. Stoy were co-authors of the article, 'The decline in summer fallow in the northern plains cooled near-surface climate but had minimal impacts on precipitation' submitted to the journal ' ' which is contained within this dissertation.; Andreas Prein and Paul C. Stoy were co-authors of the article, 'Recent enhancement of thermodynamic environments in the northern North American Great Plains' submitted to the journal 'Geophysical research letters' which is contained within this dissertation.The northern North American Great Plains (NNAGP) is the area defined by the Upper Missouri River Basin and the Canadian Prairies. It is a semi-arid region categorized by large stretches of grassland, pasture, and crops. During the last century and extending to the present day, a standard agricultural practice was to utilize a wheat-summer fallow rotation schedule, where the fields were left unplatted and an herbicide was often applied to keep weeds at bay. Concerns over soil health and profitability have led to the systematic decline of summer fallow, and nearly 116,000 km 2 that used to be fallow during the summer in the 1970s are now planted. An observational analysis discovered that from 1970-2015, during the early warm season, the NNAGP have cooled at -0.18 °C decade -1, nearly the same magnitude as the annual global warming rate. The near-surface atmosphere also moistened, evidenced by a decreasing vapor pressure deficit (VPD) trend, and monthly mean precipitation increased in excess of 8 mm per decade. Monthly mean convective available potential energy (CAPE) increased by 80% at Glasgow, MT and by 35% at Bismarck, ND based on atmospheric sounding observations. To test whether a reduction in summer fallow is responsible for these observed changes, a set of convection-permitting model experiments were performed over the NNAGP. Two sets (4 total) of three-year simulations were driven by ERA5 data with the vegetative fraction adjusted using satellite estimated fallow amounts for 2011 and 1984. The control simulations were extensively validated against an ensemble of observations with large temperature biases in Winter by ~ -3 °C and Summer by ~3°C. The areas where fallow area declined from 1984-2011 were cooler by about 1.5 °C and had a lower VPD by 0.15 kPa compared to where it did not. CAPE increased where fallow declined from 1984-2011 but so did convective inhibition (CIN). These findings insinuate that the observed change to monthly mean precipitation cannot be explained by summer fallow reduction alone. Trends in observed low level moisture transport show that the Great Plains Low Level Jet has been intensifying, bringing increased moisture to the NNAGP and partially responsible for the precipitation increase.Item Impacts of crop rotations and nitrogen fertilizer on soil biological factors in semi-arid Montana(Montana State University - Bozeman, College of Agriculture, 2021) Fouts, Willa Constance; Chairperson, Graduate Committee: Catherine A. ZabinskiEvaluating the effects of cropping and fertilizing techniques is key to informing agricultural best practices. We must continue monitoring how we manipulate soils in order to preserve and cultivate high-quality soil ecosystems that can support us in the face of climate change and widespread soil loss and deterioration. We assessed the effects of common agricultural practices in Montana by measuring biological indicators of soil quality in the 18th year of a field plot experiment with 100% and 50% the recommended rate of synthetic nitrogen (N) fertilizer and crop rotations incorporating wheat, fallow, and legumes. The biological indicators measured were four soil extracellular enzymes, potentially mineralizable N (PMN), and microbial biomass. We sampled once in spring 2020 and subsampled in the fall. We also tested whether enzymes and PMN were correlated to aboveground plant residue, which was represented by the sum of the dried plant mass from past two years left on the plots after harvest. Plant residue was positively correlated with the C, N, and S-cycling enzymes and to PMN. The positive correlation between PMN and residue reflects that increased biomass inputs could increase easily mineralizable N. Soil with the high N-rate had a slightly higher geometric mean enzyme activity. This could be from the resulting increase in plant residue. The high N-rate treatment slightly decreased soil PMN but was not affected by crop rotation treatments. Fallow systems had lower enzyme function overall, indicating a lessened fertility and decomposition rate compared to continuously cropped treatments, which keep the soil covered with a crop for more months out of the year. The positive correlations of plant residue, along with the general lower performance of the fallow systems, especially the tilled fallow rotation, support that aboveground biomass inputs are a driver in soil ecosystem function. Continuous no-till crop rotations have increased aboveground plant organic matter, which could increase nutrient cycling and decomposition, and thereby soil biological quality and fertility.Item Surface-atmosphere exchange of carbon dioxide, water, and heat across a dryland wheat-fallow rotation(Montana State University - Bozeman, College of Agriculture, 2015) Vick, Elizabeth Segourney K.; Chairperson, Graduate Committee: Paul C. Stoy; Paul C. Stoy was co-author of the article, 'The influence of dryland agriculture wheat-fallow rotation on the exchange of carbon, water, and heat with the atmosphere' submitted to the journal 'Journal of agriculture, ecosystems and environment' which is contained within this thesis.Summerfallow - the practice of keeping a field out of production during the growing season - is a common practice in dryland wheat (Triticum aestivum L.) cropping systems, including those of Montana. It is currently unknown how seasonal patterns of carbon dioxide, water, and heat flux between ecosystems and the atmosphere differ between fallow and wheat. This study quantifies the impact of dryland wheat vs. chemical fallow agricultural management practices on these important surface-atmosphere exchanges using the eddy covariance method across a winter wheat - spring wheat - fallow rotation in the Judith Basin, MT. I used a suite of meteorological sensors to measure relative humidity, air temperature, soil moisture, wind speed and direction, incident and reflected shortwave radiation, upwelling and downwelling longwave radiation, crop height, and soil heat flux to further quantify the impacts of this cropping sequence on biophysical attributes of the land surface and to model turbulent fluxes. Both wheat fields were carbon sinks on the order of 110 to 205 g C m -2 during the April to September study periods of 2013 and 2014, while the fallow field was a carbon source to the atmosphere on the order of 135 g C m -2 during the April to September study period of 2014. Evapotranspiration (ET) was over 100 mm greater in a spring wheat field than in a simultaneously measured fallow field during the 2014 study period, and modeled maximum daily atmospheric boundary layer height was up to 800 m higher in fallow compared to spring wheat. Results demonstrate that fallow has a detrimental impact to soil carbon resources yet is less water intensive, with consequences for regional climate via its impacts on atmospheric boundary layer development and global climate via its carbon metabolism.Item Pea in Rotation with Wheat Reduced Uncertainty of Economic Returns in Southwest Montana(2015-01) Miller, Perry R.; Bekkerman, Anton; Jones, Clain A.; Burgess, Macdonald H.; Holmes, Jeffrey A.; Engel, Richard E.Pea (Pisum sativum L.) is increasingly being rotated with wheat (Triticum aestivum L.) in Montana. Our objective was to compare economic net returns among wheat-only and pea–wheat systems during an established 4-yr crop rotation. The experimental design included three wheat-only (tilled fallow–wheat, no-till fallow–wheat, no-till continuous wheat) and three no-till pea–wheat (pea–wheat, pea brown manure–wheat, and pea forage–wheat) systems as main plots, and high and low available N rates as subplots. Net returns were calculated as the difference between market revenues and operation and input costs associated with machinery, seed and seed treatment, fertilizer, and pesticides. Gross returns for wheat were adjusted to reflect grain protein at “flat” and “sharp” discount/premium schedules based on historical Montana elevator schedules. Cumulative net returns were calculated for four scenarios including high and low available N rates and flat and sharp protein discount/premium schedules. Pea–wheat consistently had the greatest net returns among the six systems studied. Pea fallow–wheat systems exhibited greater economic stability across scenarios but had greater 4-yr returns (US$287 ha–1) than fallow–wheat systems only under the low N rate and sharp protein discount schedule scenario. We concluded that pea–wheat systems can reduce net return uncertainties relative to wheat-only systems under contrasting N fertility regimes, and variable wheat protein discount schedules in southwestern Montana. This implies that pea–wheat rotations, which protected wheat yield and/or protein levels under varying N fertility management, can reduce farmers’ exposure to annual economic variability.Item Weed population dynamics in diversified cropping systems of the Northern Great Plains(Montana State University - Bozeman, College of Agriculture, 2004) Hulting, Andrew Gerald; Chairperson, Graduate Committee: Bruce Maxwell.Small grain/fallow-based cropping systems of Montana and the Northern Great Plains are largely viewed as unsustainable from both an economic and environmental perspective. As a result, interest in alternative cropping systems has increased. A component of these alternative systems is increased crop diversity, but a major obstacle to adopting more diverse crop rotations is concern about weed management during the transition to the new system. I investigated changes in weed population dynamics during this transition period to some alternative systems in MT. Temporal dynamics of wild oat and redroot pigweed populations as affected by crop rotations and management intensity (conventional vs. reduced input levels) were examined. I found that crop diversity and accompanying crop management practices can be effective weed management tools during the transition to reduced input cropping systems. Crop rotation alone, however, in both the conventional or reduced input systems had little impact on weed populations when it was decoupled from corresponding chemical weed management practices. In addition, I examined the temporal and spatial dynamics of wild oat, Persian darnel, and redroot pigweed as part of the same field study. I quantified metrics that described weed population growth or decline in different crop rotations across conventional, reduced, and organic input cropping systems. A methodology for graphically depicting the combined temporal and spatial dynamics of a weed population was developed. This data set was then used to investigate the importance of variables hypothesized to be important drivers of observed wild oat population dynamics. Using multiple linear regression techniques, the best predictors of wild oat seedling abundance were determined to be wild oat seedling density and proximity to wild oat seedling density the previous growing season. The overall predictive power of our models however was low, but may indicate that wild oat populations persist in cropping systems by continuously forming new colonies in response to management more than any other single factor. Results of these studies highlight the gaps in our knowledge base related to identifying the mix of fundamental ecological processes and management that drive observed weed population dynamics. These results also demonstrate the data requirements needed to develop an understanding of weed population dynamics in agroecosystems.Item Adaptation of Australian ley farming to Montana dryland cereal production(Montana State University - Bozeman, College of Agriculture, 1982) Koala, SaidouItem Assessing changes in spatial and temporal patterns of cropping sequences in northeast Montana(Montana State University - Bozeman, College of Agriculture, 2014) Long, John Allen; Chairperson, Graduate Committee: Rick L. Lawrence; Rick L. Lawrence, Perry R. Miller, Mark C. Greenwood and Lucy A. Marshall were co-authors of the article, 'Object-oriented crop classification using multitemporal ETM+ SLC-OFF imagery and random forest' in the journal 'GIScience and remote sensing ' which is contained within this thesis.; Rick L. Lawrence, Perry R. Miller, and Lucy A. Marshall were co-authors of the article, 'Changes in field-level cropping sequences: indicators of shifting agricultural practices' in the journal 'Agriculture, ecosystems & environment' which is contained within this thesis.; Rick L. Lawrence, Perry R. Miller, Mark C. Greenwood, and Lucy A. Marshall were co-authors of the article, 'Adoption of cropping sequences in northeast Montana: a spatio-temporal analysis' submitted to the journal 'Agriculture, ecosystems & environment' which is contained within this thesis.Initiatives to mitigate the effects of climate change have focused largely on the reduction of greenhouse gas production and on carbon capture and storage technologies. Changes in agricultural management practices have shown the ability to sequester carbon by increasing soil organic carbon and include reduced tillage intensity, decreased fallow, and changing from monoculture to rotational cropping. All have become more common in portions of the Northern Great Plains; but, despite the growth of these practices, it is unknown to what extent farmers have adopted particular cropping sequences or how they have spread temporally or spatially. My purpose here was to investigate the patterns of changing agricultural practices in northeast Montana during 2001-2012 by focusing on the increased adoption of cereal-pulse sequences and the adoption of block-managed cereal-based sequences in lieu of continuous strip-cropping. A method to identify crops via geospatial data and Landsat imagery was developed, and annual crop maps were created. Crop classifications were extracted from the maps for each field to create a 12-character string for the temporal sequence of crops, and specific 2- and 3-yr sequences were identified with a string-matching algorithm. Finally, I examined the observed spatial patterns of sequence adoption to determine if observed spatial patterns were random or were they consistent with the spread and adoption due to social interaction as described in innovation diffusion theory, adoption based on environmental factors, or neither. The major findings were: (1) cereal-fallow rotations, whether managed in blocks or by strip-cropping, no longer dominate the region; (2) there has been a substantial increase in the adoption of cereal-pulse sequences; (3) producers did not adhere strongly to specific sequences; (4) using 3-yr sequences added no additional information than 2-yr sequences; (5) the adoption of these practices was not randomly located but clustered; and (6) the adoption of these practice are not well-explained by innovation diffusion theory, although social interactions might have played a role in the early stages; the patterns are more consistent with suitability of the physical environment since available water was strongly associated with whether or not a field was managed with either practice.Item Effects of alternative management practices on the abundance of arthropods in a mixed-crop agroecosystem(Montana State University - Bozeman, College of Agriculture, 2013) Gill, Paramjit Singh; Chairperson, Graduate Committee: Kevin O'NeillWe evaluated the effects of alternative management practices on the abundance and diversity of arthropods in a mixed-crop agroecosystem in studies conducted in 2010 and 2011 at the Fort Ellis Experimental Station near Bozeman, MT. In one study, we quantified arthropod relative abundance in plots across three summer fallow weed management practices (sheep grazing, mechanical/tillage, and chemical herbicide) incorporated into a three-year rotation in two different sets of crops. Arthropod abundance was compared among 1) the spring wheat plots under the three management schemes with the rotational treatments (continuous spring wheat and rotational spring wheat), 2) the pea/hay barley plots under the different weed management schemes, and 3) fallow plots under the three weed management schemes. In a second study, we examined arthropod relative abundance in plots with alternative alfalfa cultivars (Cimarron SR, HayGrazer, and Shaw). Sweep net samples were taken to compare the abundances of the most common insect orders and families (as well as a few abundant species and genera). In addition, baited traps were used to compare the abundance of click beetle larvae or wireworms (Coleoptera: Elateridae) within the different management schemes and treatments. This study demonstrated that the number of arthropods in the continuous spring wheat was lower compared to the rotational spring wheat. Arthropod abundance in the pea/hay barley plots under the three different managements was inconsistent from one year to the other. In the summer fallow plots, abundance of most arthropod taxa was the lowest in the mechanically-treated plots, whereas there was no difference in the number of most arthropods present between the chemical and grazed plots which shows that sheep grazing was equally effective as the application of herbicides in reducing arthropod numbers on summer fallow plots. The abundance of most arthropod taxa did not differ among the Cimarron SR, HayGrazer, and Shaw alfalfa cultivars except for Aphididae, Formicidae, and Ichneumonidae in 2010. Nine species of wireworms were collected from the study site with Aeolus mellilus Say being the most common. In both years, A. mellilus was most abundant in the continuous spring wheat plots compared to the other plots.Item Weed seedbank dynamics and composition of northern Great Plains cropping systems(Montana State University - Bozeman, College of Agriculture, 2007) Harbuck, Kristin Suzanne Bates; Chairperson, Graduate Committee: Fabian D. Menalled.With a growing concern about sustainability of agricultural production systems, interest in integrated weed management systems has increased. Increasing the understanding of weed seedbank dynamics will improve efficiency of management. The objectives of this study were to 1) quantify weed seedbank dynamics in response to seed density and burial depth, 2) determine weed seedbank decay at varying seed densities and burial depths, 3) quantify weed seed predation in wheat and tilled fallow fields, and 4) characterize and compare weed seedbanks in organic and conventional no-tillage production fields. Objective 1 was carried out at Montana State University's Arthur H. Post Agronomy Farm. Seedbanks were established at four densities and two burial depths. Weekly seedling counts were taken for two consecutive growing seasons. Data indicated higher density seedbanks had lower proportions of emergence. Individual species responded differently to depth treatments. We concluded that management affecting seed density and depth will affect seedling emergence. Objective 2 was carried out in the same plots as objective 1. Seedbank samples were used to separate seeds.Item Seeking sustainability for organic cropping systems in the northern Great Plains : legume green manure management strategies(Montana State University - Bozeman, College of Agriculture, 2007) Izard, Erica Jean; Chairperson, Graduate Committee: Perry R. Miller.Soil fertility in organic cropping systems of the northern Great Plains (NGP) is most often achieved through inclusion of leguminous green manures. The objectives in this study were to evaluate the efficacy of pea as green manure; and more specifically, measure the effects of pea green manure type, termination timing and method for soil water use and soil N contribution. A study consisting of winter pea, spring pea, mustard, buckwheat and fallow was conducted at Big Sandy Montana. In Bozeman, MT, termination methods of winter and spring pea were compared. Green manures were terminated at one of two timings, first bloom or first pod. Winter pea was the superior annual green manure in this study, optimizing the soil water conservation and N fertility goals of organic dryland growers in the NGP. Winter pea terminated at bloom also provided the greatest soil N at the end of the green fallow period relative to other green manures. However, pod-terminated winter pea may enhance soil N fertility due to greater N fixation over the long-term.