Utilization of Poultry Litter and Plant Growth-Promoting Rhizobacteria to Improve Crop Productivity
Type of DegreePhD Dissertation
Crop Soils and Environmental Sciences
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In order to satisfy the demand for food on a global scale, more than 180 million tons of chemical fertilizers are applied annually to increase crop yields. However, the consequences of indiscriminate chemical fertilizer use are a significant environment problem leading to soil degradation which may negatively affect several soil ecological functions. There are also strong indications that phosphorus supplies used for fertilizers are limited, indicating a need to more efficiently utilize and recycle phosphorus back into agricultural soils. Poultry litter and plant growth-promoting rhizobacteria could be used as alternatives to chemical fertilizers. If utilized appropriately, they are environmental-friendly and can contribute towards the promotion of plant growth and crop yield. Thus, the main aim of this dissertation was to evaluate the impact of poultry litter and plant growth-promoting rhizobacteria use on plant growth and productivity under different environmental conditions and management practices. This dissertation consists of five parts: (1) Effect of poultry litter on grain yield and crop productivity in a wheat-soybean double-cropping system; (2) Effect of nitrogen fertilization on winter canola yield and nitrogen uptake; (3) Effect of PGPR on corn growth under different fertility sources; (4) Effect of PGPR on corn growth at various nitrogen rates; and (5) Effect of PGPR on corn growth under drought stress. In the first study, wheat and soybean yield were evaluated in a two-year field experiment. Greater wheat yields were observed when both poultry litter and inorganic N were applied, indicating that fertilization practices combining poultry litter and inorganic N may be an alternative to just applying inorganic chemical fertilizer for the growth and productivity of wheat. The increased soybean grain yield observed under double cropping suggests that a combination of poultry litter and inorganic N fertilizer use for a wheat-soybean cropping system could provide sustainable yield production. In the second study, plant biomass, grain yield, and N uptake of winter canola increased with increasing N application rates, with optimal yields occurring when 197 to 232 kg N ha-1 was applied to these southeastern US soils. Moreover, applying both poultry litter and inorganic N fertilizer to agricultural fields could reduce the dependence on solely using chemical fertilizers without decreasing winter canola yields, thereby providing sustainable yield production for winter canola in the southeastern US. In the third study, the selected PGPR strains improved plant growth parameters and biomass accumulation in the early growth stages of corn and the performance varied with different fertility sources. However, applying N at recommended rates may have masked the influence of PGPR on corn growth. Thus, PGPR inoculation with different N rates was evaluated in the fourth study, and showed that the selected PGPR strains with a half-dose of N fertilization could promote corn growth and produce corn biomass and N concentration equal to or greater than that of uninoculated full N fertilization rate. In the fifth study, the selected PGPR strains increased corn root morphology, thereby improving aboveground growth and biomass accumulation of corn under water stress. Overall, utilization of poultry litter and plant growth-promoting rhizobacteria could improve plant growth and produce biomass or grain yield comparable to standard fertilization practices and potentially reduce some of the dependency on chemical fertilizer usage.