Theses and Dissertations at Montana State University (MSU)
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Item Pulse crop management to enhance biological nitrogen fixation in the northern Great Plains(Montana State University - Bozeman, College of Agriculture, 2022) Baber, Kaleb Wade; Chairperson, Graduate Committee: Clain Jones; Clain Jones, Perry Miller, Sydney Atencio, Samuel Koeshall and Peggy Lamb were co-authors of the article, 'Lentil nitrogen fixation response to fertilizer and inoculant in the northern Great Plains' submitted to the journal 'Agronomy journal' which is contained within this thesis.; Clain Jones, Kevin McPhee, Perry Miller and Peggy Lamb were co-authors of the article, 'Assessment of nitrogen fixation among pea and lentil varieties in the semiarid northern Great Plains' submitted to the journal 'Agronomy journal' which is contained within this thesis.Pulse crop production has increased dramatically in Montana and the surrounding northern Great Plains over the past few decades. Through N fixation, pulse crops, including pea and lentil, can reduce N fertilizer requirements, both by replacing non N-fixing crops and positively contributing to soil N pools for subsequent crop uptake. Three studies were conducted in Montana over three years to investigate pulse crop management practices that enhance N fixation of pea and lentil. The first study investigated lentil N fixation response to fertilizers and inoculant types. Inoculant and S fertilizer each increased N fixed by lentil in 40% of site-years, but response was not well correlated with cropping history or soil sulfate-S levels. In one site-year, N fixation appeared to continue increasing at the highest tissue S concentration while seed yield plateaued below that highest level, indicating that S fertilizer could increase the soil N benefit of lentil even if a yield response is not expected. Potassium fertilizer nor inoculant type influenced N fixed. The second study assessed differences in N fixation among lentil and pea varieties. Amounts of N fixed varied in 75% and 50% of site-years for lentil and pea, respectively. Differences among varieties were sometimes large, up to 45 kg N ha-1. Two lentil varieties, CDC Richlea and Riveland, were frequently among the top N-fixers, while no pea varieties consistently fixed more N than others. Correlations between N fixed and seed yield ranged from weak to moderate, and pea more frequently had positive relationships than lentil. The third study evaluated N fixation response of two pea varieties to inoculant formulations. Inoculant formulation did not impact N fixed by either variety, and the uninoculated treatment performed as well as the inoculated treatments. This suggests producers may not need to inoculate pulse crops to achieve sufficient N fixation when effective rhizobia populations exist in their fields. These results contribute to the researchers' understanding of N fixation by pulse crops in the region. Together, these studies can help producers in the northern Great Plains better manage pea and lentil, improving both economic and environmental sustainability of the region's cropping systems.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.Item Symbiotic nitrogen fixation and establishment of six Montana native legumes species(Montana State University - Bozeman, College of Agriculture, 2005) Metcalf, Sarah Jean; Chairperson, Graduate Committee: Jeff Jacobsen.Legume species have been known to increase soil N content and are incorporated into land restoration seed mixes in hopes of improving degraded soils and plant communities. The goals of this project were to determine effects of soil type, soil moisture, inocula and fungicide treatments on legume establishment, N2 fixation capacity and plant biomass for six individual native legume species. In potted greenhouse studies, legumes were grown in five field soils to verify nodulation without inocula. In a second phase, plant biomass was measured in two soils at two moisture contents (60 and 80% of field capacity). The efficacies of Rhizobia inocula and fungicide treatments were also tested. The greenhouse studies were used to supplement data gathered at three field sites around Montana. Native soils contained Rhizobia that were specific to many of the plant species tested and induced nodulation. Soil moisture content, inoculation and fungicide treatments had less effect on nodulation and biomass than the soil characteristics. Fungicide treatments benefited establishment of Lupinus argenteus, and had mixed effects on Astragalus canadensis and Dalea candida. Benefits were dependent on soil nutrient content, microbial biota and other characteristics. Shoot biomass at each field site also varied significantly; in general A. canadensis had the highest nodulation and biomass, while Dalea purpurea and D. candida typically had the lowest biomasses and nodulation. This research should assist land managers in selecting species to suit a wide variety of ecological conditions and land restoration scenarios.Item Pollinators of slender white prairieclover(Montana State University - Bozeman, College of Agriculture, 2008) Pearce, April Marie; Chairperson, Graduate Committee: Kevin O'Neill; Sue Blodgett (co-chair)Slender white prairieclover (Dalea candida) is a perennial angiosperm, grown at Bridger plant materials center (BMPC) for reclamation purposes. Interest in the pollinators and pests of this plant developed at BPMC following the death of a 5year old stand. The objectives of these experiments were to (1) determine the diversity and identify the potential pollinators on D. candida and other cultivated and non-cultivated angiosperm species using sweep samples and pan traps; (2) determination of pollen load size and composition of individual insects collected on angiosperm plant species; (3) use of different size exclusion cages to determine the general sizes of insects most important for pollination of D. candida at BPMC; and (4) determine the composition of the community of cavity-nesting Hymenoptera species at BPMC by using trap nests. The overall diversity of BPMC was much higher than expected in a monoculture agriculture area, with a total of 102 Hymenoptera taxa collected. Hill's #2 index was used to determine the diversity of different angiosperm plants and revealed that D. candida had the highest diversity. Analysis of pollen loads via the proportion of "pure" vs. mixed loads (PBP) and mean proportion of conspecific pollen (PCP) revealed conflicting results between the two measures, but there does appear to be some floral constancy occurring, especially in D. candida. Kruskal-Wallis tests of differences in exclusion cage treatments revealed that there are differences in pollination efficacy and the size subset allowed to reach the flowers. Emergences from trap nests revealed differences in the trap nesting community at BPMC and actual pollinator collections in the field.Item Greening summer fallow : agronomic and edaphic implications of legumes in dryland wheat agroecosystems(Montana State University - Bozeman, College of Agriculture, 2011) O'Dea, Justin Kevin; Chairperson, Graduate Committee: Perry Miller.; Perry R. Miller and Clain A. Jones were co-authors of the article, 'Greening summer fallow with legume green manures: on-farm assessment in North-Central Montana' in the journal 'Journal of Soil and Water Conservation' which is contained within this thesis.; Clain A. Jones, Catherine A. Zabinski, Ilai N. Keren and Perry R. Miller were co-authors of the article, 'Legume, cropping intensity, and N-fertilization effects on attributes and processes in soils from an eight-year-old semiarid wheat system' in the journal 'Plant and Soil' which is contained within this thesis.Adopting nitrogen (N)-fixing legumes into crop rotations is an accessible, ecological practice capable of increasing agricultural sustainability. Nonetheless, in northern Great Plains (NGP) wheat systems, proper water use management and the realization of N benefits are barriers to legumes replacing summer fallow. Legumes should also be able to mitigate legacies of soil organic matter losses from summer fallow. We conducted a participatory field-scale study in north-central Montana, assessing the viability of no-till, early-terminated legume green manures (LGMs) as summer fallow replacements. Soil water and nitrogen were measured to evaluate LGM effects on subsequent wheat crops. Farmers were interviewed to elucidate perspectives and challenges of adopting LGMs. Compared to fallow, LGMs depressed subsequent wheat yields by 6% (0.24 Mg ha -¹), and lowered grain protein at sites where wheat was fertilized with N (9 g kg -¹); grain protein was increased at unfertilized sites (5 g kg -¹). Absent rotational benefits from LGMs were attributed to dry conditions in the LGM year leading to low LGM biomass N and reduced N mineralization potential in soils, rather than soil water limitation to subsequent wheat. Farmers were curious about possible longterm benefits from LGMs, but expressed that the economic viability of LGMs appeared tenuous in the short-term. We also examined attributes and processes in soils from an eight-year-old rotation study containing fallow-wheat, continuous wheat, and legume-inclusive no-till rotations. We examined potentially mineralizable C and N (PMC and PMN), microbial biomass-C and wet aggregate stability (WAS). Nitrogen fertilizer was also added to a duplicate set of soils, and effects on C and N mineralization were evaluated. Legume-inclusive systems generally had higher levels of soil parameters, and had 26-50% greater PMN than wheat-only systems. Systems returning the most crop residue C to the soils had higher WAS regardless of legumes. Nitrogen additions depressed C and N mineralization. Results of these studies suggest that in NGP agroecosystems, LGMs can avoid limiting soil water available to subsequent wheat when terminated early and managed as no-till crops, but that legumes should be viewed as an investment in soil quality which may precipitate rotational N benefits more reliably after three or more appearances in rotation.