Life Sciences Commons^™

Management Zone Delineation Techniques On Irrigated Corn In Nebraska, Aaron M. Bereuter

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

Increased interest in site-specific management of irrigated corn in Nebraska has identified the need for a decision-making framework for zone delineation. Zones based on static soil and landscape properties provide a valuable foundation for variable rate management strategies. The purpose of this project was to identify the optimal soil and landscape attributes for generating management zones (MZ) of relative productivity potential. Three producer-managed cornfields across Nebraska with varying soil types, topographic characteristics, and climate regimes were identified as research sites during the 2010 growing season. Nine soil and landscape attributes were identified as potential properties for estimation of productivity potential. …

Impact Of Crop And Residue Management On The Physical And Chemical Stabilization Of Soil Organic Matter At Farm Level, Ana B. Wingeyer

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

This dissertation explores changes over time in soil organic matter (SOM) stabilization of two irrigated production fields: a continuous maize sequence that was converted from no-till to conservation deep tillage (Site 1), and a no-till maize-soybean rotation (Site 2). An integrated approach using humic acid extractions and density-based physical fractionation of SOM within aggregate size classes was developed to evaluate the changes in SOM stabilization (physical protection, organo-mineral associations and humification). At Site 1, loss of SOM in the surface layer was compensated for by increased SOM in deeper soil layers with no net change in C stocks. Whole field …

Integration Of Plant-Based Canopy Sensors For Site-Specific Nitrogen Management, Luciano S. Shiratsuchi

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

The soil’s nitrogen (N) supply can vary drastically in the field, spatially as well as temporally making any soil prediction difficult even with very detailed mapping. Consequently, a plant-based approach wherein the measured canopy can indicate the N needs in a reactive and spatially-variable way can be a better approach than mapping, because integrate the soil N supply and translate the crop need on-the-go. The first experiment evaluated the performance of various spectral indices for sensing N status of corn, where spectral variability might be confounded by water-induced variations in crop reflectance. We found that water and previous crops effects …

Gata-Family Transcription Factors In Magnaporthe Oryzae, Cristian F. Quispe

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

The filamentous fungus, Magnaporthe oryzae, responsible for blast rice disease, destroys around 10-30% of the rice crop annually. Infection begins when the specialized infection structure, the appressorium, generates enormous internal turgor pressure through the accumulation of glycerol. This turgor acts on a penetration peg emerging at the base of the cell, causing it to breach the leaf surface allowing its infection.

The enzyme trehalose-6- phosphate synthase (Tps1) is a central regulator of the transition from appressorium development to infectious hyphal growth. In the first chapter we show that initiation of rice blast disease requires a regulatory mechanism involving an …

The Rate Of Shattercane X Sorghum Hybridization In Situ, Jared J. Schmidt

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

Cultivated sorghum (Sorghum bicolor subsp. bicolor) can interbreed with its close weedy relative shattercane (S. bicolor subsp. drummondii). The introduction of traits from cultivated sorghum into a shattercane population could contribute to the invasiveness of the wild shattercane population. An in situ experiment was conducted across two years to determine the potential for pollen-mediated gene flow from grain sorghum to shattercane. Shattercane with juicy midrib (dd) was planted in a soybean field in concentric arcs at varying distances from a sorghum pollen source with dry midrib (DD). The arcs were placed so …

Transpiration-Use Efficiency Coefficient Of Seven Weed Species As Affected By Fraction Of Transpirable Soil Water And Growth Stage, Venkatarao Mannam

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

Transpiration-use efficiency coefficient (Kc) describes the amount of biomass produced per unit transpiration at a given vapor pressure deficit. A series of greenhouse experiments were conducted to determine the K_c values of seven weed species and to measure how K_c values were affected by fraction of transpirable soil water (FTSW) level and plant growth stage. Experiments were conducted using a factorial design with 4 levels of water stress (0.3, 0.4, 0.7, and 1.0 FTSW) and two harvest times (first bloom and seed maturity). After plants attained a predetermined size, each plant was sealed at the base using a …

Herbicide-Resistant Risk Assessment: Response Of Common Nebraska Weeds To Dicamba Dose, Roberto J. Crespo

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

Dicamba-resistant soybeans are being developed to provide an additional herbicide mechanism of action that can be used in soybean, and to provide a tool to help manage or mitigate the evolution of other herbicide-resistant weed populations. The objectives of this thesis were to assess the risk of common Nebraska weeds developing resistance to dicamba, quantify baseline dose-response to dicamba of high-risk weed species, and survey the variability in dicamba dose-response among populations of those species. Twenty-five weed scientists were asked to estimate the risk likelihood of ten weed species evolving resistance to dicamba following the commercialization of dicamba-resistant soybean. Palmer …