Climate change impacts on agriculture have been widely researched in recent years. In Sub-Saharan Africa, many of these studies have focused on spatially aggregate impacts at the country or higher level, and typically do not discuss the heterogeneities of impacts within a region. Thus, there is a growing interest in more localized climate change impacts modeling that could help inform regional adaptation within a country. In this study, we utilize a panel of Ghanaian subnational district-level corn yields matched to weather data that is spatially interpolated from observed station data to identify whether warming impacts exhibit spatial heterogeneities for corn yields. Findings show spatial heterogeneities of yields across main and non-main corn growing areas, as well as various ecological zones and also at the district level. Furthermore, findings indicate that extremely high temperature would have negative impacts on yields in main corn-growing areas, meanwhile, impacts are expected to be insignificant in non-main corn growing areas. This study will be helpful in informing future research as well as food security and stability adaptation decisions related to climate change in Ghana. Keywords: corn, yields, climate, change, zones, Ghana

A stochastic benefit-cost analysis is used to analyze the profitability of irrigating from an Onarm water storage (OFWS) system using a center pivot irrigation system (CPIS) compared to a rained production system for corn and soybean in the Southeast while also incorporating risk in the form of stochastic prices, yields and weather. Findings indicate that producer’s decision to invest in an OFWS is dependent on the existing rate of returns and risk aversion levels. When costs are paid upront, net present values for irrigating from an OFWS are lower than that of rainfall when discount rates are just above 2%. Higher net present values for irrigation relative to rainfall production are realized when the cost of investment is financed rather than making an upront payment at higher discount rates. Investing in an OFWS on small farm sizes is not a good option for risk averse producers but, under extreme risk aversion levels, decision makers may prefer to irrigate and insure their revenue at higher coverage levels than depend on rainfall. Cost assistance opportunities for crop producers to prevent downstream flow of nutrients from production fields through the use OFWS should be more than 40% to make irrigation more desirable than dryland production at 8% and 10% discount rates.

The absolute abundances of fission-product xenon and krypton isotopes in six uranium minerals were determined mass spectrometrically using the isotope dilution technique. The fission products were resolved into a U spontaneous fission component, a U 235 neutron-induced fission component, and a U 238 neutron-induced fission component. The presence of U 238 of neutron-induced fission indicated that t he neutron energies in uranium minerals were higher than had been suspected. Internal consistency in the analysis was achieved only when the I 29 yield in u235 thermal neutron fission reported by Purkayastha and Martin was lowered by 20%. The number of U 238 spontaneous fissions was calculated from the lead age, U 238 content, and the U 238 pontaneous fission half life. A comparison of the number of fission products from U 238 spontaneous fission and the number of spontaneous fissions in each of the six minerals showed that five of the six minerals had lost large portions of their noble gases. A fractionation of krypton relative to xenon accompanied this loss. The results obtained for the sixth mineral indicated little or no loss of xenon and krypton. Absolute yields for U 238 spontaneous fission were therefore determined from an analysis of this mineral. / Thesis / Doctor of Philosophy (PhD)

Isotopic abundances of the elements barium, cerium, neodymium, samarium and europium formed in the thermal neutron fission of have been studied with a mass spectrometer. Suitable analyses of very young and old fission products have made possible the normaliza­tion of the isotopic abundances of each of these elements through iso­baric nuclides. In this manner the relative cumulative fission yield of every fission chain from mass 137 to 154 has been obtained. These yields, together with previously reported relative yields of masses 131 to 137 when normalized to total 100%, give the absolute cumulative yield of all the significant heavy fragment chains. The origin of the fine structure found in this mass yield distribution is discussed. It has been found that all fine structure can be explained in terms of a smooth primary mass-yield curve and a simple neutron distribution both of which are compared with experimental data from other laboratories. / Thesis / Doctor of Philosophy (PhD)

No description available.

M.S.

Grain sorghum is the principal food crop in Botswana. It is often grown in low fertility, coarse-textured soils. It is a common practice within some ethnic groups in Botswana to remove the primary panicle with the expectation that this will increase the grain yield by promoting tillers. A factorial experiment was conducted in the greenhouse to investigate the effect of panicle removal at anthesis and N on growth and yield of grain sorghum. Two N rates (25 or 100 kg/ha), three cultivars (Segaolane, Northrup King 2660, and Korwane), two main panicle treatments (present or removed), and five replications were used. Panicle removal increased the number of tillers and kernel weight but decreased yield (by reducing kernel number) in Segaolane and NK 2660. The kernel weight in Korwane did not respond to panicle treatments, but grain yield was reduced by panicle removal. In all cultivars, photosynthesis was reduced when the main panicle was removed. Korwane invested more assimilates in vegetative material (harvest index = 0.15), while Segaolane and NK 2660 partitioned more photosynthates into grain yield (harvest index = 0.5). Nitrogen application increased total dry matter, tillers, grain yield, and number of kernels in each variety except that Korwane was not responsive in kernel number. Nitrogen fertilization decreased kernel weight in two of the varieties but not Korwane. Kernel weight of Korwane was not affected by any of the treatments in this test. In summary, panicle removal appeared not to be a positive management practice for increasing grain yield of any of the varieties studied. On the other hand, N fertilization was beneficial to yield. / Master of Science

Thesis (MScAgric (Agronomy))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: See full text for the abstract / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

No description available.

No description available.