Theses and Dissertations at Montana State University (MSU)
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Item Precision organic agriculture(Montana State University - Bozeman, College of Agriculture, 2023) Loewen, Royden Alexander Sasha; Chairperson, Graduate Committee: Bruce D. Maxwell; This is a manuscript style paper that includes co-authored chapters.Organic agriculture addresses some of the shortcomings of industrialized conventional agriculture, but is prevented from more mainstream uptake by reduced yields. Organic agriculture relies on knowledge of intricate biological interactions in place of synthetic inputs used in other forms of agriculture, and in this way reflects an older way of practicing agriculture. Precision agriculture (PA) conversely is a technologically driven method of farming and combines guidance and data collection via remote sensing technologies to bring new efficiencies to farm operations. In this dissertation PA tools were used to explore the potential of improving organic production through site-specific management. By conducting on farm precision experiments (OFPE) with PA farmers can learn quickly about spatial variability across fields enabling well defined management templates. In organic systems this experimentation can be conducted with varied seeding rate inputs of both cover and cash crops. Here, we explored the relevancy of PA in organic settings, first broadly laying the philosophical foundation for the paradigm shift from production-oriented agriculture to precision agroecology. Secondly, a greenhouse experiment was used to develop the first-principle relationship between cover crop and cash crop seeding rates to maximize net return, establishing the basis for field experiments. Field scale experiments on five organic grain farms across the northern great plains deployed OFPE to optimize net returns, or suppress weeds, with varied seeding rates of cover and cash crops. Based on OFPE data, simulations across all sites found net returns could be improved on average by $45.82 ha-1 if economically optimum variable seeding rates were used. While seeding rates were found to have variable effects on weeds across fields, an optimized site-specific seeding strategy to balance net return and weed minimization improved net return and weed suppression compared to farmer-chosen seeding rates in every field tested. Overall, these results reveal the relevancy of precision agriculture to be deployed in organic systems to improve management for increased farmer net returns, and as a weed management method. In this way modern tools can be used to augment farmer knowledge about their local spaces to enable greater understanding and improved management of complex agroecosystems.Item Population dynamics of wheat stem sawfly, Cephus cinctus Norton, in barley in Montana(Montana State University - Bozeman, College of Agriculture, 2020) Achhami, Buddhi Bahadur; Chairperson, Graduate Committee: David K. Weaver; Gadi V. P. Reddy, Jamie D. Sherman, Robert K. D. Peterson and David K. Weaver were co-authors of the article, 'Antixenosis, antibiosis, and potential yield compensatory responses in barley cultivars exposed to wheat stem sawfly under field conditions' which is contained within this dissertation.; Gadi V. P. Reddy, Jamie D. Sherman, Robert K. D. Peterson and David K. Weaver were co-authors of the article, 'Effect of precipitation and temperature on larval survival of Cephus cinctus (Hymenoptera: Cephidae) in barley cultivars' which is contained within this dissertation.; Robert K. D. Peterson, Jamie D. Sherman, Gadi V. P. Reddy and David K. Weaver were co-authors of the article, 'Multiple decrement life tables of Cephus cinctus Norton (Hymenoptera: Cephidae) across a set of barley cultivars: the importance of plant defense versus cannibalism' which is contained within this dissertation.; Gadi V. P. Reddy, Megan L. Hofland, Robert K. D. Peterson, Jamie D. Sherman and David K. Weaver were co-authors of the article, 'Host selection and oviposition behaviors of Cephus cinctus (Hymenoptera: Cephidae) in barley' which is contained within this dissertation.Wheat stem sawfly (WSS) is an economically devastating pest of cereals grown in North America. The larva is the only feeding stage and remains confined within a host stem until it emerges as an adult the following year. This limited mobility increases larval vulnerability to mortality factors when host plant traits are hostile to survival. For instance, larval mortality is greater in barley than in solid stemmed wheat cultivars known to be resistant. Both solid stemmed wheat and barley kill neonates via host plant resistance traits. Traditionally, barley was recommended as an alternative rotational crop to prevent WSS outbreaks in wheat crops. There is limited data available regarding barley host plant resistance and questions persist. Has barley resistance changed over time? What is the impact of larval feeding injury on grain yield of barley? Do females display similar oviposition behaviors across barley cultivars that vary in susceptibility? To answer these questions. I conducted field experiments to assess resistance and possible tolerance to WSS in eight barley cultivars. Based on the number of eggs, 'Hockett' was the most attractive cultivar to WSS female (less antixenosis), while 'Craft' and 'Celebration' killed the greatest number of neonates due to antibiosis. Multiple decrement life table studies revealed that plant defense and cannibalism were two major causes of larval mortality. We measured greater yield in infested stems with dead larvae (potential tolerance) than for cut stems and both were greater than uninfested stems in all cultivars except 'Celebration'. A greenhouse study revealed that females preferred 'Hockett' over 'Craft' in frequencies of oviposition behaviors and numbers of eggs deposited. Additionally, a greater amount of the WSS attractant (Z)-3-hexenyl acetate was found in aerations from 'Hockett' plants than from 'Craft.' The amount of defensive compound linalool was greater in aerations from 'Craft' than from 'Hockett.' These results suggest that barley cultivars are equipped with varying levels of antibiosis, antixenosis, and tolerance traits against WSS. Thus, we can exploit these traits in the development of cultivars which can reduce WSS populations and decrease economic loss caused by this species.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 Water stress in Montana cropping systems: effects of cultivar, management, and environment on crop production in dryland systems(Montana State University - Bozeman, College of Agriculture, 2016) Bestwick, Michael Linn; Chairperson, Graduate Committee: Richard E. Engel; Chengci Chen (co-chair)Crop productivity--defined as yield, protein, and economic returns--hinge on crop water use. Crop water use is a function of genetic, environment, and management factors. This thesis addresses how these factors interact with crop water use and productivity in Montana. In chapter 2, a two-year (2014-2015) study compared winter wheat yield and protein following fallow and three intensive sequences on deep and shallow soils. Water extraction was measured on deep soils, and kriged soil depth estimates served as a surrogate for stored soil moisture on shallow soils. On deep soils, yields ranged from 72-84% of fallow-wheat from 20.5 mm less water extracted below 45 cm, while protein was ~0.63% greater in intensified sequences. On shallow soils, sequence did not affect yield or protein. Yields increased with soil depth while protein decreased in 2014, but no trends were observed in 2015 due to 47 mm greater precipitation from joint to heading. Intensive sequences diminish wheat productivity on deep soils, whereas soil depth and precipitation timing control productivity on shallow soils. In chapter 3, state-wide cultivar testing, soils, and climate data was used to quantify four general drought patterns in winter wheat and five in pea. Cultivar had little impact on yield compared to drought pattern with winter wheat yields ranging from 4421 kg ha -1 to 2539 kg ha -1 and pea yields ranging from 2877 kg ha -1 to 975 kg ha -1. Yields negatively correlated with drought intensity at heading in wheat (r 2=-0.79) and flowering in pea (r 2=-0.76). Quantifying drought patterns provides a physical interpretation to improve management and breeding efforts. In chapter 4, yield-evapotranspiration (ET) functions were derived for spring wheat, pea, and chickpea from a three-year (2002-2004) seeding date trial. Yield-ET functions were coupled with ten-year (2005-2015) climate records to predict yields at four staggered seeding dates. Yield predictions were converted to marginal revenues based on high, medium, and low markets and fixed production costs. Across seeding dates and markets, simulated returns were highest for chickpea (~601 $ ha -1) followed by wheat (372 $ ha -1) and pea (202 $ ha -1). This indicates chickpea should be seeded before wheat and pea.Item Fallow replacement and alternative fertilizer practices : effects on nitrate leaching, grain yield and protein, and net revenue in a semiarid region(Montana State University - Bozeman, College of Agriculture, 2015) John, Andrew Augustus; Chairperson, Graduate Committee: Clain JonesHigh nitrate concentrations in groundwater have been observed in agricultural regions worldwide. In the Judith River Watershed of central Montana, groundwater nitrate concentrations have increased from 10 to 23 mg L-1 over the span of 20 years. Nitrate leaching from agricultural fields is a major concern for growers and stakeholders in the region. Little research has been conducted in dryland semiarid regions on the effects of agricultural practices on nitrate leaching. We conducted a 2-yr study comparing three alternative management practices (pea rotation, controlled-release urea, split nitrogen application) to grower standard practices (fallow, conventional urea, spring broadcast urea) on grain yield, grain protein, net revenue, and the amount of nitrate leached. Eight field treatment interfaces were established across three farms and each treatment was in duplicate per year. Ten soil and biomass sampling locations were designated on both sides of the interface. Net revenue was calculated by enterprise budgets constructed from local and state data. Nitrate leaching was calculated using a nitrogen mass balance equation. Replacing pea with fallow decreased winter wheat grain yield and protein yet had no effect on net revenue during the first year of the study (2013). In the second year, pea-winter wheat earned $83 ha -1 more (P<0.1) than fallow-winter wheat. Neither fertilizer alternative management practice had an effect on net revenue. In the 2013 treatment year, wheat after pea leached less nitrate (20 kg N ha -1) than wheat after fallow (56 kg N ha -1), indicating more deep percolation of nitrate with fallow practice. In the 2014 treatment year, a greater amount of nitrate leached (P<0.1) while using controlled-release urea than conventional urea, possibly in part because the controlled release urea was applied earlier than conventional urea. The results of our study revealed that replacing fallow with pea can decrease the amount of nitrate that leaches out of the root zone. Also, this practice either increased or had no effect on net revenue, revealing its ability to be economically feasible for a grower to implement. Based on our findings, future research should likely focus on practices that decrease rates of deep percolation.Item Using the soil-crop yield database to evaluate and improve a productivity index (PI) model for small grains in Montana(Montana State University - Bozeman, College of Agriculture, 1993) Lorbeer, Scott HenryItem Soil and terrain attributes for predicting soil fertility and winter wheat yield(Montana State University - Bozeman, College of Agriculture, 1993) McEachern, Kirk LowndesItem Use of soil parameters to assess crop yield potential in Gallatin Valley, Montana : a study of soil quality(Montana State University - Bozeman, College of Agriculture, 1999) Saleh, ArsilItem Wheat yield estimates using multi-temporal AVHRR-NDVI satellite imagery(Montana State University - Bozeman, College of Agriculture, 1999) Henry, Mari Patricia