Rhizosphere and soil bacteria are important drivers in nearly all biochemical cycles in terrestrial ecosystems and participate in maintaining health and productivity of soil in agriculturally managed systems. However, the effect of agricultural management systems on bacterial communities is still poorly understood. In this study, cultural methods and advanced molecular methods (terminal restriction fragment length polymorphism (TRFLP) and 454- pyrosequencing) were used to identify shifts in soil and rhizosphere bacterial diversity, community composition, and functions under different cropping systems in Manitoba, Canada. This included monoculture vs. rotation, zero tillage vs. conventional tillage, and organic farming vs. conventional farming. Results showed that: (1) different cropping systems did not significantly influence the diversity of bacterial communities. However, a significant variation in relative abundances of bacterial communities at both the phylum and genus level was observed among different cropping systems. Compared to conventional farming systems, organic farming system had a higher percentage of the phylum Proteobacteria (many Plant Growth Promoting Rhizosbacteria) and a lower percentage of the phylum Actinobacteria. When canola monoculture was compared to wheat-oat-canola-pea rotation, a significantly higher percentage of Proteobacteria and a lower percentage of Actinobacteria were found in the rotational system. Wheat monoculture shared similar bacterial communities with wheat-oat-canola-pea rotation. Zero tillage did not change bacterial community profiles except for an increase in Firmicutes (many PGPR), compared to conventional tillage. At the genus level, significant differences were found for the dominant genera Pseudomonas, Rhizobium, Stenotrophomonas, Brevundimonas, Burkholderia, Marmoricola, Microlunatus, and Solirubrobacter. The bacterial distribution was strongly associated with soil pH. (2) The cropping systems also influenced the antibiotic-producing Pseudomonas populations determined through PCR-based screening for the detection of genes involved in the biosynthesis of antibiotics. It was found that pyrrolnitrin- and phenazine- producing Pseudomonas spp. were more prevalent in the soil under zero tillage and organic farming systems, while 2,4-DAPG and pyoluteorin-producing strains were not found in this study. This comprehensive study provided fundamental information on how different cropping systems affect soil and rhizosphere bacterial communities, which can be used to guide Manitoba farmers to choose proper farming systems to maintain soil health and increase PGPR populations in soil.

Nitrous oxide (N2O) produced from agricultural activities must be determined if management procedures to reduce emissions are to be established. From 1994 to 1996, N20 emissions were determined under continuous corn and corn-legume rotations in different soils of Quebec. Continuous corn was studied on four sites, two from a long-term experiment, a Ste. Rosalie heavy clay (Humic Gleysol) and a Chicot sandy loam (Gray-Brown Luvisol), at 0, 170,285 and 400 kg N ha-1, and two from a corn rotation study, a Ste. Rosalie clay (Humic Gleysol) and an Ormstown silty clay loam (Humic Gleysol). Treatments in the rotation study included no-till (NT) and conventional tillage (CT), monocropped corn, monocropped soybean-, corn-soybean; and soybean-corn-alfalfa phased rotations. Nitrogen rates of 0, 90, and 180 kg N ha-1 for corn and 0, 20, and 40 kg N ha-1 for monocropped soybean were used, and soybean/alfalfa with no fertilizer N following corn. Rates of N2O emissions were significantly affected by N fertilization, tillage and soil moisture content. Generally, N2O emissions were higher in the NT systems, with corn, and increased with increasing N rates. Increased nitrogen applications led to linear increases in N2O emission over the three years for both Ste. Rosalie (2) and Ormstown soils at a rate of 1.0 to 1.6 percent of added N. The N 2O emission rates were significantly related to soil denitrification rates, water filled pore space, and soil NH4+ and NO3-- concentrations in all three years. A corn system using conventional tillage, legumes in rotation and reduced N fertilizer would decrease N2O emission from agricultural fields.

Thesis (MSc. Sys. Ag. (Honors))--University of Western Sydney, Hawkesbury, 1994. / "A thesis presented in fulfilment of the requirement of the Degree of Master of Science (Hons) in Systems Agriculture."

Thesis (M.Sc.(Agric.))--University of Western Australia, 2006.

Thesis (Ph.D.). / Written for the Dept. of Natural Resource Sciences. Title from title page of PDF (viewed 2008/07/23). Includes bibliographical references.

Thesis (M. S.)--Michigan State University. Dept. of Crop and Soil Sciences, 2006. / Title from PDF t.p. (viewed on June 19, 2009) Includes bibliographical references (p. 94-99). Also issued in print.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 101-105). Also available via the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 182-195). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 182-195). Also available on the Internet.

Thesis (Ph. D.(Agric.)) (Agronomy)--University of Pretoria, 2009. / Includes summary. Available in print and online. Includes bibliographical references.