|dc.description.abstract||Encouraging progress towards commercial production of cellulosic biofuels has recently raised the importance of identifying economically feasible and environmentally sustainable cellulosic biomass supply chains. In this regard, dedicated cellulosic energy crops are superior to agricultural residues due to their higher yield which results in less area needed to produce a given quantity of biomass and, therefore, lower transportation costs. A substantial amount of research has been conducted on perennial cellulosic energy crops such as switchgrass (Panicum virgatum L.), giant reed (Arundo donax L.) and mimosa (Albizia julibrissin Durazz.), but relatively little attention has been paid to annuals that could be rotated with existing row crops without competing with them for land. Moreover, little or no information is available on long-term (>10 years) yields and soil impacts of energy crops and the yield responses to critical economic factors. Therefore, the overall goal of research reported in this dissertation was to evaluate yield and soil impacts of selected potential energy crops for the southeastern United States.
The first-two experiments of the project evaluated three common winter annuals (black oat (Avena strigosa Schreb.), rye (Secale cereale L. subsp. cereale) and annual ryegrass (Lolium multiflorum Lam.)) and three summer annuals (forage sorghum (Sorghum bicolor spp.), pearl millet (Pennisetum americanum (L.) R. Br.) and sorghum-sudangrass (Sorghum bicolor (L.) Moench nothosubsp. drummondii (Steud.) de Wet ex Davidse)) in a range of crop rotation systems. Compared to black oat and ryegrass, rye was the most suitable winter crop for biomass production in rotation with cotton
(Gossypium hirsutum L.), peanuts (Arachis hypogaea L.) and soybeans (Glycine max (L.) Merr.). For the three winter annuals in rotation with the three summer crops for year-round biomass production, with either conventional-till or no-till management, double-cropping systems that included pearl millet or forage sorghum under no-till management were superior to other cropping systems under either tillage treatment in the first year. However, within each tillage treatment, double-cropping systems that included forage sorghum or sorghum-sudangrass were superior to other cropping systems in the second and third years.
The other five experiments in the project evaluated giant reed, mimosa and switchgrass for biomass production. Giant reed and mimosa provided much higher biomass yield than switchgrass in long-term experiments, even though they received no fertilization, while switchgrass received a medium amount of N fertilizer annually. In contrast to traditional summer row crops such as corn, cotton and soybeans, rainfall did not have large effects on biomass yields of these three perennials, and neither did age of stand. Biomass yield of switchgrass increased at a declining rate as N levels increased, but subsoiling did not improve yield and interseeding crimson clover actually decreased yield. Biomass yield of giant reed was not improved by application of broiler litter. While there was no difference in biomass yield between annual and biennial harvests in winter, biennial harvesting will likely result in lower cost Mg-1. Biomass production of giant reed was reached a maximum in mid-September to mid-November. Long-term biomass production of giant reed and switchgrass tended to decrease topsoil pH and extractable Mg and Ca contents compared to an adjacent area under bahiagrass (Paspalum notatum Flüggé), and giant reed seemed to increase extractable P and K.||en_US