Thesis (Ph. D.)--University of Queensland, 2001. / Includes bibliographical references.

Graduation date: 1998

Conditions within maize (Zea mays L.) fields can cause plant-to-plant variability (PPV) because of emergence, spacing, and mid-season growth non-uniformities. PPV has been associated with yield reductions in maize. Maize growers can influence field conditions and maize yields through management practices such as rotation and tillage. The objectives of this research were to determine the effect that tillage and crop rotation systems have on maize growth and PPV, and whether PPV is a mechanism for yield differences observed among management systems. Field experiments were conducted at the Elora Research Station in Ontario, Canada in 2010 and 2011, where maize was grown under various tillage and rotation treatments. Plant-level measurements were taken throughout the season. Diverse crop rotations and conventional tillage (CT) increased grain yields. Maize grown in no-tillage (NT) treatments had later seedling emergence, lower leaf numbers throughout the season, shorter plants at silking, later anthesis and silking, and lower plant grain yields compared to CT treatments. Rotations that incorporated alfalfa or cover crops had earlier silking dates and fewer plants that were developmentally delayed compared to mono-crop rotations. PPV was characterized using variance (s2) and the coefficient of variation (CV), but the two approaches did not drastically change the outcome of the study. Tillage more consistently altered PPV than rotation treatments. NT had higher variability in emergence, leaf number, silking date, plant spacing, anthesis-silking interval, and harvest index than CT. Higher variability in emergence, early-season leaf number, dry matter at silking,and harvest index were found to be mechanisms for lower yields in NT treatments. This research suggests that producers should take measures to limit variability in these parameters due to their associations with yield reductions, especially when growing maize in NT systems.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph.D.Agric.(Agronomy))-University of Pretoria, 2009. / Includes bibliographical references (leaves 75-87). Available in print and online.

No description available.

Thesis (M.Sc) (Agriculture)--University of Limpopo, 2007. / Cowpea (Vigna unguiculata L. Walp) is one of the important food legumes and a valuable component of the traditional cropping systems. It serves as a source of protein in human diet and plays a major role in animal nutrition. The crop is adaptable to harsh environments including extreme temperatures and water limiting conditions. There is limited information available in cowpea with regards to cultivar selection and performance studies across ranges of environments in South Africa. The objectives of the present study were to 1) determine the influence of different planting dates and locations on phenology, yield and yield components of selected cowpea varieties and 2) determine the relationship of seed yield to environmental conditions such as rainfall and temperature. Ten cowpea genotypes were used for the study, developed by the Agricultural Research Council, Grain Crops Institute, South Africa. The experiment was laid out in a randomized complete block design with three replications. The experiment was carried out at Potchefstroom, Taung (Northwest Province) and Syferkuil (Limpopo Province) during three planting dates viz. 8 Nov. 22 Nov and 6 Dec. 2004. Data collected included the number of days to 50% flowering, number of days to 50% physiological maturity, seed yield, number of branches per plant, number of pods per plant, number of seeds per pod and 100 seed weight. The results showed highly significant differences among cowpea genotypes in each location and across locations for yield and yield components. Planting date one (i.e. 08 November) was better in yield gain over all locations. Potchefstroom was the best location for best yield gain due to high rainfall and relatively favorable low temperatures. The lowest yield was recorded at Syferkuil because of low rainfall and high temperatures. With relatively better performance across locations IT18E-16, CH14 and Pan311 were the best genotypes recommended in these or other similar environments in South Africa. / National Research Foundation (NRF)and Agricultural Research Council (ARC)

No description available.

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.