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Nitrous Oxide Emissions From Smooth Bromegrass Pasture Under Nitrogen Fertilizer And Ruminant Urine Application In Eastern Nebraska, Laura K. Snell

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Nitrous oxide (N₂O) is a greenhouse gas primarily produced in soils by denitrifying and nitrifying organisms. Agricultural soils account for 70% of emissions in the United States, but little data is available for contributions from managed pasture ecosystems. This study focused on the production of N₂O in smooth bromegrass (Bromus inermis Leyss.) pastures established on silt loam soils in eastern Nebraska. Thirty smooth bromegrass plots (1.5m x 1.5m) were treated with five different fertilizer treatments (0, 45, 90, 135, and 180 kg N/ha) and two urine treatments (urine and no urine). Herbage sampling was taken …

Organellar Signaling Expands Plant Phenotypic Variation And Increases The Potential For Breeding The Epigenome, Roberto De La Rosa Santamaria

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

MUTS HOMOLOGUE 1 (MSH1) is a nuclear gene unique to plants that functions in mitochondria and plastids, where it confers genome stability. Phenotypic effects of MSH1 down- regulation were studied in sorghum inbreed line Tx430 and Arabidopsis ecotype Columbia-0, with the hypothesis that RNAi suppression of MSH1 triggers retrograde signaling from organelles to the nucleus, alters the epigenome, and derives heritable phenotypic variation suitable for artificial selection. An array of morphological traits and metabolic pathways was detected, including leaf variegation, male sterility and dwarfism, associated with altered gibberellic acid metabolism, higher levels of reactive oxygen species (ROS), and decreased synthesis …

Nest And Brood Site Selection And Survival Of Greater Prairie-Chickens In The Eastern Sandhills Of Nebraska, Lars Anderson

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Greater prairie-chickens (Tympanuchus cupido pinnata) are a grassland bird species of conservation concern. Although greater prairie-chickens have declined over much of their range, the Nebraska Sandhills has the largest population in North America. However, the responses of nest and brood site selection and survival to vegetation characteristics are unknown. I studied prairie-chickens on private rangelands in Rock and Brown Counties from 2009-2011. I fitted 139 females with radio collars to locate nest and brood sites and to determine nest and brood survival rates. Females were trapped on leks during the breeding season and I monitored them throughout the …

Integrated Management Of Common Reed Along The Platte River In Nebraska: Control, Timing, Water Use, And Economic Analysis, Ryan E. Rapp

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

There are two biotypes of common reed, which includes the native common reed (Phragmites australis subsp. americanus) and non-native (invasive) common reed (Phragmites australis subsp. australis).The non-native biotype of common reed has invaded wetland habitats in many states of the US, including Nebraska.

Three studies, disking followed by herbicide, mowing followed by herbicide, and herbicide followed by mechanical treatment were initiated in 2008 in Nebraska. The objective was to evaluate common reed control along the Platte River using an integrated management. Herbicide followed by mechanical treatment had excellent control (≥92%) with all treatments except glyphosate applied …

Diversification Of Organic Cropping Systems With Cover Crop Mixtures: Influence On Weed Communities, Soil Microbial Community Structure, Soil Moisture And Nitrogen, And Crop Yield, Samuel E. Wortman

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Organic grain cropping systems typically depend on intensive mechanical cultivation for weed control and manure or compost applications to meet plant nutrient demands. However, cover crops may contribute to weed suppression and soil fertility, potentially increasing crop yield and sustainability of the system. The utility of individual cover crop species have been well documented, but the agronomic benefits of diverse cover crop mixtures have received less attention. Cover crop mixtures are an appealing option for farmers, as increasing species diversity has been shown to increase resource-use efficiency, stability, resiliency, and productivity of plant communities. Despite the growing interest in cover …

Understanding The Biology, Inheritance And Mechanism Of Resistance Of 2,4-D Resistant Waterhemp (Amaranthus Tuberculatus) - Research Proposal, Roberto Crespo

Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research

Waterhemp is a very well adapted summer annual weed to the U.S. Corn Belt region. Auxinic herbicides such as 2,4-D constitute effective and widely used herbicides to control waterhemp and other broadleaf species in cereal crops and turf grasses. Recently, Bernards et al. (2012) have reported a Nebraska waterhemp biotype has evolved resistant to 2,4-D. This finding represents the sixth mode-of action herbicide group to which waterhemp has evolved resistance to. Several attributes may have contributed to make waterhemp a very successful weed and prone to evolve to herbicide resistant: a high genetic variability, aggressive growth habits and high fecundity. …