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Bibliography: leaves 140-153 / xi, 153, [84] leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The aims of this research were to assess the tolerance of L. pilosus to calcareous soils, to identify intraspecific variation through the development of screening methods and to propose physiological and genetic reasons for genotypic differences. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 2000

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

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Precipitation reactions of phosphorus (P) with Ca decrease the P fertilizer efficiency in calcareous soils. The hypothesis was that anion competition of sulphate with phosphate to precipitate with Ca will increase P solubility in calcareous soils. Initial experiments were conducted to investigate the effect of co-application of K2SO4, (NH4)2SO4, MgSO4 and (NH4)2CO3 on the solubility of monopotassium phosphate (MPP) and monoammonium phosphate (MAP) in different Manitoba soils. Co-application of sulphate salts enhanced P solubility by a factor that ranged from 6% to 44% in soils with greater exchangeable Ca and smaller acid-extractable Ca content (i.e. Osborne, Red River, Balmoral and St. Claude soil series). Solubility and solid-state speciation of P were investigated when MPP was banded with sulphate salts in both model and natural (Dezwood Loam soil series, DL) calcareous soils. The results of S K-edge X-ray absorption near edge structure spectroscopy (XANES) showed that CaSO4•2H2O was formed in DL soil when either K2SO4, (NH4)2SO4 or MgSO4 was applied with MPP. Phosphorus-31 magic-angle spinning nuclear magnetic resonance (MAS NMR) analysis showed that dicalcium phosphate dihydrate (DCPD) was formed in both soils, but the relative proportion of DCPD decreased in the presence of sulphate salts due to the formation of a new P compound. The results also showed that decreasing Ca saturation on the cation exchange complex increased the solubility and mobility of MAP in model calcareous soils and Ca played a more dominant role in forming P precipitates than Mg. According to 31P MAS NMR results, DCPD was the dominant P species in soils with 100% to 50% Ca saturation on the cation exchange complex while poorly ordered magnesium phosphate trihydrate was the prominent P phase with 70% to 100% Mg saturation. This study has demonstrated that the combination of solid state NMR and XANES provided complimentary information concerning anion competition and changes in P speciation due to the co-application of sulphate salts in fertilizer bands. Application of sulphate salts is a promising agronomic practice to enhance P solubility in soils with greater exchangeable Ca content due to the anion competition by sulphates with phosphate to precipitate with Ca.

The microclimate of plants growing close to the ground is strongly influenced by the orientation of a soil/vegetation surface with respect to the sun's rays (slope and aspect). In chalk grassland in the UK, slopes of contrasting aspect frequently have distinctive patterns of vegetation. A series of climatic and microclimatic measurements were made at field sites indifferent regions on the English chalk (North Dorset and the Yorkshire Wolds) during the period June 2000 to September 2002. Using digital terrain models (DTMs), process-based models of microclimatic variables at different points in the landscape were developed. The mechanisms through which topography may influence vegetation and species distribution were investigated with field experiments and measurements. Both existing vegetation data from Perring (1956) and new data collected from the field sites were analysed using detrended correspondence analysis (DCA) and generalised additive models (GAMs), to elucidate the relationships between vegetation and soil, topography and climate. A consistent gradient in chalk grassland vegetation was found across spatial scales, associated with the frequency of species with a "stress tolerant” strategy. This gradient in vegetation is apparently driven by species' responses to several separate, but often correlated, variables including soil moisture, maximum summer temperatures and soil fertility. Over the past 50 years, stress tolerant species have declined in frequency at the North Dorset field site, Ellenberg fertility indices have increased and light indices have decreased. The observed changes are consistent with fertilization from atmospheric N deposition and/or relaxation of rabbit grazing after the myxomatosis outbreak in the 1950s. Plots on sloping ground, and in particular, south-west facing slopes, were least affected by these changes, suggesting that high temperatures, phosphorus and water limitation have acted as a buffer against vegetation change, and that complex topography creates refuges for stress tolerant species in the landscape.

Thesis (M.S. - Soils, Water and Engineering)--University of Arizona. / Includes bibliographical references.

Thesis (Ph.D.) -- University of Adelaide, Dept. of Plant Science, 2000. / Bibliography: leaves 140-153.