The use of fossil fuels contributes to global warming and there is a consequent need to resort to clean and renewable fuels. The major concerns with using agricultural crops for the production of energy are food and water security. Crops that do not threaten food security and that can be cultivated with a relatively low amount of water and produce high yields of fermentable sugars are therefore needed. Sweet sorghum is a fastgrowing crop that can be harvested twice a year and that can produce both food (grain) and energy (sugar juice from stems). Sweet sorghum bagasse can also be utilised for ethanol production. The aim of this study was to determine the sugar content of different sweet sorghum cultivars at different harvest times, and determine the cultivar that will produce the highest ethanol yield at optimized fermentation conditions. Sweet sorghum bagasse was also pretretated, enzymatic hydrolysed and fermented and the best pretreatment method and ethanol yield was determined. In this study, sweet sorghum juice, which mostly consists of readily fermentable sugars (glucose, sucrose and fructose), as well as the bagasse obtained after juice extraction, were converted to bio–ethanol. Sweet sorghum juice was fermented to ethanol using Saccharomyces cereviciae without any prior pretreatment. The effect of pH (4–6), yeast concentration (1–5g.L–1), initial sugar concentration (110–440g.L–1) and the addition of a nitrogen source (urea, ammonium sulphate, yeast extract and peptone) on the ethanol yield was investigated. The pretreatment of bagasse using sulphuric acid (3wt %), and calcium hydroxide (0.2g/g bagasse), followed by enzymatic hydrolysis using Celluclast 1.5L (0.25g/g bagasse), Novozyme 188 (0.24g/g bagasse) and Tween 80(1.25g.L–1) were adapted from Mabentsela (2010). Fermentation was done using Saccharomyces cerevisiae, but it was unable to ferment the xylose sugar. The results show that the USA 1 cultivar contains the highest sugar content at 3 months. An ethanol and glycerol yield of 0.48g.g–1 and 0.05g.g–1 was observed respectively at a pH of 4.5, a yeast concentration of 3wt%, initial sugar concentration of 440g.L–1 and when ammonium sulphate was added to the fermentation broth as nitrogen source. The glycerol yield formed as a by–product during fermentation and at a maximum ethanol yield was 0.05g.g–1. The glucose yield obtained from sulphuric acid, base and ultrasonic wave pretreatment was 0.79g.g–1, 0.62g.g–1 and 0.62g.g–1 respectively. The glucose yield obtained after each type of pretreatment was higher than that obtained for unpretreated bagasse, which was 0.55g.g–1. Base pretreatment, ultrasonic wave pretreatment and unpretreated bagasse also contained fructose at the end of enzymatic hydrolysis. Base, sulphuric acid pretreatment disrupted the crystal structure of cellulose and increased the available surface, and therefore cellulose was easily accessible for enzymatic hydrolysis. Ultrasonic wave pretreatment showed potential in increasing the surface area for enzymatic hydrolysis but further investigations need to be done. From bagasse fermentation, 0.45g.g–1 – 0.39g.g–1 of ethanol per g of available fermentable sugar was obtained. / Thesis (M.Sc. Engineering Sciences (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.

The use of fossil fuels contributes to global warming and there is a consequent need to resort to clean and renewable fuels. The major concerns with using agricultural crops for the production of energy are food and water security. Crops that do not threaten food security and that can be cultivated with a relatively low amount of water and produce high yields of fermentable sugars are therefore needed. Sweet sorghum is a fastgrowing crop that can be harvested twice a year and that can produce both food (grain) and energy (sugar juice from stems). Sweet sorghum bagasse can also be utilised for ethanol production. The aim of this study was to determine the sugar content of different sweet sorghum cultivars at different harvest times, and determine the cultivar that will produce the highest ethanol yield at optimized fermentation conditions. Sweet sorghum bagasse was also pretretated, enzymatic hydrolysed and fermented and the best pretreatment method and ethanol yield was determined. In this study, sweet sorghum juice, which mostly consists of readily fermentable sugars (glucose, sucrose and fructose), as well as the bagasse obtained after juice extraction, were converted to bio–ethanol. Sweet sorghum juice was fermented to ethanol using Saccharomyces cereviciae without any prior pretreatment. The effect of pH (4–6), yeast concentration (1–5g.L–1), initial sugar concentration (110–440g.L–1) and the addition of a nitrogen source (urea, ammonium sulphate, yeast extract and peptone) on the ethanol yield was investigated. The pretreatment of bagasse using sulphuric acid (3wt %), and calcium hydroxide (0.2g/g bagasse), followed by enzymatic hydrolysis using Celluclast 1.5L (0.25g/g bagasse), Novozyme 188 (0.24g/g bagasse) and Tween 80(1.25g.L–1) were adapted from Mabentsela (2010). Fermentation was done using Saccharomyces cerevisiae, but it was unable to ferment the xylose sugar. The results show that the USA 1 cultivar contains the highest sugar content at 3 months. An ethanol and glycerol yield of 0.48g.g–1 and 0.05g.g–1 was observed respectively at a pH of 4.5, a yeast concentration of 3wt%, initial sugar concentration of 440g.L–1 and when ammonium sulphate was added to the fermentation broth as nitrogen source. The glycerol yield formed as a by–product during fermentation and at a maximum ethanol yield was 0.05g.g–1. The glucose yield obtained from sulphuric acid, base and ultrasonic wave pretreatment was 0.79g.g–1, 0.62g.g–1 and 0.62g.g–1 respectively. The glucose yield obtained after each type of pretreatment was higher than that obtained for unpretreated bagasse, which was 0.55g.g–1. Base pretreatment, ultrasonic wave pretreatment and unpretreated bagasse also contained fructose at the end of enzymatic hydrolysis. Base, sulphuric acid pretreatment disrupted the crystal structure of cellulose and increased the available surface, and therefore cellulose was easily accessible for enzymatic hydrolysis. Ultrasonic wave pretreatment showed potential in increasing the surface area for enzymatic hydrolysis but further investigations need to be done. From bagasse fermentation, 0.45g.g–1 – 0.39g.g–1 of ethanol per g of available fermentable sugar was obtained. / Thesis (M.Sc. Engineering Sciences (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.

Field experiments were conducted during the 1989 dry season (July to December) at the Manggoapi Farm of the Faculty of Agriculture, Cenderawasih University in Manokwari, Irian Jaya, Indonesia. The objectives of the experiments were to determine the effects of four sweet potato cropping systems on the population density of sweet potato weevils (SPW) and on the diversity of other insects within these agroecosystems. / Fewer SPW were found in intercropped sweet potato + corn (2 weevils per kg infected tubers), sweet potato + soybean (21 weevils), sweet potato + corn + soybean (8 weevils) than in monoculture sweet potato (37 weevils); percentage of damaged tubers followed the same trend, ranging from 2.6% to 14.0% in intercropped sweet potato, to 21.9% in the sweet potato monoculture. However, the higher number of SPW and damaged tubers in the monoculture did not reduce yield below that in the intercropped plots. / Insect and spider populations were more diverse in the intercropped sweet potato systems than in monoculture. Number of arthropods increased throughout the growing season. Intercropping may reduce the population density of other insect pests associated with sweet potato and may increase the population density of natural enemies.

The effect of serial (multiple-year) organic matter (OM) amendment on soil properties has been described in some cropping systems, although less is known about the effect of serially amended field soils on soil-borne plant diseases. The objectives of this study were to describe the effects of the third and fourth years of annual, serial amendment with dairy manure solids on 1) soil physical and biological properties and 2) severity of sweet corn root rot. Plots were amended with five rates of separated dairy manure solids annually for three years. In the fourth year, plots were split and only half of each plot was re-amended. Soil physical properties [bulk density, free and occluded particulate organic matter (POM), soil water retention, total porosity, gravimetric moisture content] and biological properties [microbial activity (as hydrolysis of fluorescein diacetate; FDA) and microbial biomass-C] were assessed each year in all treatments. Root rot severity was assessed in situ and in the greenhouse with multiple sweet corn (Zea mays L. cv Golden Jubilee) bioassays conducted in the amended field soils. Necrosis of the radicle and nodal roots was assessed when plants reached the 6- leaf stage. Amendment rate was positively associated with increases in soil properties that serve as indicators of soil quality, such as POM content, total porosity, microbial biomass, and FDA activity. In the third year after amendment, weak root rot suppression was observed in-field and was associated with FDA activity. By the fourth year of serial amendment this trend was no longer evident, however evidence from the high-rate treatment that was not re-amended (3HNRA) pointed to an emerging suppressive mechanism that persisted up to 13 months after the third amendment. Factors that may be interacting over time to generate observed disease suppression in these serially amended soils include: short-term post-amendment microbiostasis, soil moisture retention, inoculum potential, and a novel suppressive mechanism. / Graduation date: 2006

Recent initiatives for biofuel production have increased research and development of sweet sorghum. Currently, the initial major limitation to integrating sweet sorghum into existing production systems is the lack of sweet sorghum hybrids adapted to industrial production systems. Hybrid development is now underway, and the application of genetic markers can be used to define the genetic basis of sugar yield and its components, as well as reduce the time required to deliver new sweet sorghum hybrids to market. The purpose of this research was to further characterize the genetic components that influence sweet sorghum productivity, agronomics, and composition. Specifically, a grain x sweet sorghum recombinant inbred line (RIL) population developed for quantitative trait locus (QTL) analysis related to sugar production was evaluated for 24 phenotypic traits including brix, percent moisture, and biomass yield across four environments. The 185 F4 RILs were derived from the parents 'BTx3197' and 'Rio', which are pithy stalk grain and juicy stalk sweet sorghums respectively. Following screening, two genetic maps were constructed with 372 and 381 single nucleotide polymorphisms (SNPs) evaluated using an Illumina GoldenGate assay. Analysis of the data in QTL Cartographer revealed a major and previously reported QTL for soluble solids on chromosome 3, but in contrast to previous studies, this QTL co-localized with other QTLs that have a negative influence on biomass and seed production. Therefore, selection for this QTL may not be advantageous. Because only a few QTLs for percent moisture were found, the results indicated that the pithy stalk phenotype does not have a major effect on percent moisture as measured in this study. Thus, breeding for high or low moisture content will be more challenging than previously expected. The absence of dominance effects indicated that brix must be high in both parents to produce high brix in the hybrid.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 5 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2004. / Härtill 4 uppsatser.

Thesis (Th. M.)--Dallas Theological Seminary, 2003. / Includes bibliographical references (leaves 42-45).

Thesis (Th. M.)--Dallas Theological Seminary, 2003. / Includes bibliographical references (leaves 42-45).

Thesis (Th. M.)--Dallas Theological Seminary, 2003. / Includes bibliographical references (leaves 42-45).