Theses and Dissertations at Montana State University (MSU)
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Item Effect of summer fallowing, perennial crop cover and conservation reserve practices on soil nitrate distribution(Montana State University - Bozeman, College of Agriculture, 1994) Pannebakker, Lynn S.; Chairperson, Graduate Committee: Jim BauderDryland agriculture is an economically feasible method of producing crops in some parts of the semi-arid regions of the mid-west and western United States. Summer fallowing, which is commonly practiced in these regions, serves to replenish soil moisture and plant-available nitrate-nitrogen (N0 3--N), while also stabilizing production and more uniformly distributing the work load. In areas where dryland agriculture is concentrated, summer fallowing may lead to N0 3--N contamination of ground-water due to lack of plant uptake of excess water and N. Under certain conditions of precipitation, soil percolation, slope, and cropping intensity, summer fallowing has been shown to cause elevated N03--N concentrations in shallow groundwater wells. These elevated N0 3--N levels have been detected in several areas of the U.S. Two areas where high N0 3--N concentrations have been repeatedly found in groundwater samples are in northeastern and central Montana. Judith Basin and Fergus Counties of Montana were selected for soil sampling to assess any differences in soil NO3--N concentrations under three different land use systems: 1) crop fallow rotation, 2) acreage enrolled in the USDA Agricultural Stabilization and Conservation Service (ASCS) conservation reserve program (CRP), 3) and rangeland. Soil samples were collected to a depth of three m (10 ft) at four different sites in each county. Soil samples from all sampling depths at each of the eight sites were analyzed for gravel percent (>2 mm diameter) , N0 3--N load, and N0 3--N concentration. Samples from 0 m to 0.6 m were also analyzed for total-N concentration. Trends in soil N0 3-N give evidence that summer fallowing may be the cause of N0 3--N in shallow groundwater in some areas Of Montana where dryland cropping is practiced. Overall, average soil N0 3--N concentration throughout the sampled soil profile was 4.2, 2.0, and 1.3 mgkg-1 for the crop fallow, CRP, and rangeland land use practices, respectively. Average N0 3--N concentration in Fergus County ranged from 2.5 mgkg-1 to 20.4 mgkg-1 under crop fallow while it ranged from only 0.9 to 6.2 mgkg-1 and from 0.9 to 4.2 mgkg-1 for the CRP and rangeland uses, respectively. Average N0 3--N concentration in Judith Basin County ranged from 1.4 mgkg-1 to 6.9 mgkg-1, 0.6 mgkg-1 to 2.0 mgkg-1, and from 0.8 mgkg-1 to 1.4 mgkg-1 under crop fallow, CRP, and rangeland land use systems, respectively. Assuming that extensive use of crop fallow causes increased N0 3--N concentrations under some conditions, alternative land use management practices may be effective in reducing N0 3--N levels in such areas.Item Nitrogen fertilizer strategies and empirical models for rainfed spring wheat(Montana State University - Bozeman, College of Agriculture, 1994) Mahmood, ShaukatItem Evaluating selected soil morphological, classification, climatic, and site variables that influence dryland small grain yield on Montana soils(Montana State University - Bozeman, College of Agriculture, 1984) Burke, Thomas HaroldItem Dryland cereal grain yield relationships with soil, environmental and crop management factors in Montana(Montana State University - Bozeman, College of Agriculture, 1990) Spencer, Linda AnnItem Adaptation of Australian ley farming to Montana dryland cereal production(Montana State University - Bozeman, College of Agriculture, 1982) Koala, SaidouItem 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.