IMPROVING FARM MANAGEMENT DECISIONS BY ANALYZING SITE-SPECIFIC ECONOMIC DATA DEVELOPED FROM YIELD MAPS

This thesis examines the use of precision agriculture data, specifically yield maps, for makingsite-specific economic decisions for improved farm management. The adoption of precisionagriculture on farms has allowed producers to collect a greater quantity and more specificinformation about production than ever before. With such information, site-specific decisions canbe made. Incorporating economic data with yield map data, two primary decision examples aredeveloped: defining areas of production and nonproduction and managing temporal risk spatiallyacross a field. Included with the production/ nonproduction decision are the effects that landtenure arrangements and risk aversion levels have on the decision. The risk maps are developedusing break-even analysis, the coefficient of variation, and a mean-variance framework, all based ona twenty year average of temporal net returns, measured spatially. The risk maps are repeatedincorporating a crop insurance option, a commonly used risk management tool. Results show thatdeveloping these maps can be used by agricultural producers to help with their decision making. Byincorporating these maps into the decision-making process, decisions can be made to increase farmprofitability

Diffusion of Iodine and Rhenium in Category 3 Waste Encasement Concrete and Soil Fill Material

Assessing long-term performance of Category 3 waste cement grouts for radionuclide encasement requires knowledge of the radionuclide-cement interactions and mechanisms of retention (i.e. sorption or precipitation). This understanding will enable accurate prediction of radionuclide fate when the waste forms come in contact with groundwater. A set of diffusion experiments using carbonated and non-carbonated concrete-soil half cells was conducted under unsaturated conditions (4% and 7% by wt moisture content). Spiked concrete half-cell specimens were prepared with and without colloidal metallic iron addition and were carbonated using supercritical carbon dioxide. Spikes of I and Re were added to achieve measurable diffusion profile in the soil part of the half-cell. In addition, properties of concrete materials likely to influence radionuclide migration such as carbonation were evaluated in an effort to correlate these properties with the release of iodine and rhenium

Lianas Suppress Seedling Growth and Survival of 14 Tree Species in a Panamanian Tropical Forest

Lianas are a common plant growth form in tropical forests, where they compete intensely with trees, decreasing tree recruitment, growth, and survival. If the detrimental effects of lianas vary significantly with tree species identity, as is often assumed, then lianas may influence tree species diversity and community composition. Furthermore, recent studies have shown that liana abundance and biomass are increasing relative to trees in neotropical forests, which will likely magnify the detrimental effects of lianas and may ultimately alter tree species diversity, relative abundances, and community composition. Few studies, however, have tested the responses of multiple tree species to the presence of lianas in robust, well‐replicated experiments. We tested the hypotheses that lianas reduce tree seedling growth and survival, and that the effect of lianas varies with tree species identity. We used a large‐scale liana removal experiment in Central Panama in which we planted 14 replicate seedlings of 14 different tree species that varied in shade tolerance in each of 16 80 × 80 m plots (eight liana‐removal and eight unmanipulated controls; 3136 total seedlings). Over a nearly two‐yr period, we found that tree seedlings survived 75% more, grew 300% taller, and had twice the aboveground biomass in liana‐removal plots than seedlings in control plots, consistent with strong competition between lianas and tree seedlings. There were no significant differences in the response of tree species to liana competition (i.e., there was no species by treatment interaction), indicating that lianas had a similar negative effect on all 14 tree species. Furthermore, the effect of lianas did not vary with tree species shade tolerance classification, suggesting that the liana effect was not solely based on light. Based on these findings, recently observed increases in liana abundance in neotropical forests will substantially reduce tree regeneration, but will not significantly alter tropical tree species diversity, relative abundance, or community composition