THE NATURE OF COPPER, ZINC AND BORON IN PRAIRIE SOILS AND CROP RESPONSES TO FERTILIZATION
Deficiencies of the micronutrients copper (Cu), zinc (Zn) and boron (B) occasionally arise in cropping systems of the Canadian prairies. However, the ability to conclusively identify the deficiencies, accurately predict response to fertilization, and provide sound recommendations for best management strategies are still lacking. Inconsistent yield responses of cereals, pulses and oilseeds to micronutrient fertilization on the prairies reflect the complex interaction of soil, crop and environmental factors that are still not clearly understood. The research described in this dissertation was conducted to provide a more comprehensive understanding of the factors affecting the nature of Cu, Zn, and B in prairie soils and their fate when added as fertilizer for alleviating site and crop specific deficiencies. The influence of several important factors including soil type, crop species and cultivars, nutrient interaction and reactions, management practices such as fertilizer formulation, rate and placement strategies, and environmental conditions were evaluated with particular emphasis on crop responses and fertilizer nutrient fate in soils. A combination of advanced chemical and spectroscopic speciation analyses were conducted on soils to identify initial and residual reaction products in contrasting soils as affected by soil conditions, environment and fertilizer management practices. Forty-four soils collected from across the prairies were used, and wheat, pea and canola were employed as test crops for responses to Cu, Zn, and B, respectively. Controlled environment and field studies were utilized to evaluate soil and crop responses and effects and interactions among factors. Reduced availability and soil supply of micronutrients were generally associated with soils of coarse texture, low organic matter and droughty soil moisture. Under these conditions, a greater response of spring wheat and canola to Cu and B fertilization was observed in controlled environment conditions. Durum wheat appeared to be more sensitive to Cu deficiency than other classes of wheat. There was no positive yield response of any pea cultivars to Zn fertilization. Pea were identified as a crop that was able to exude higher amount of citric acid that likely helps in mobilizing Zn and other micronutrient metals in the rhizosphere. Fertilization with Cu and Zn was not effective in promoting crop growth under sub-optimal environmental (dry) and P deficient soil conditions. In fact, application of both Cu and Zn together on soils of low P status had negative effects on wheat yield that may be related to an impact on metabolic processes in the plant involving these nutrients early on in the growth cycle. Soil assessments of micronutrient availability including extracting solution concentrations and supply rates were not always effective in predicting response to fertilization. Soil application of micronutrient fertilizer rather consistently increased the extractable available concentration and supply rate in initial and post-harvest soils, therefore indicating that a portion of micronutrient applied is available for crop utilization in the year of application and subsequent years. The majority of the soil-applied micronutrient fertilizers were proportionately speciated into water soluble, exchangeable, oxide and organic bound fractions according to the adsorption affinity of Cu, Zn, and B to these soil constituents. Collectively, the X-ray absorption near-edge structure (XANES) spectroscopy confirmed that native Cu and Zn were predominantly associated with carbonates, and that applied fertilizer is likely to be adsorbed to carbonate minerals and organic matter in forms that are potentially bioavailable.
Micronutrient fertilization, yield responses, fertilizer fate, mobility and bioavailability, chemical and spectroscopic speciation
Doctor of Philosophy (Ph.D.)