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Doctor of Philosophy




Yield responses of soybeans (Glycine max, L) and wheat (Tritcum aestivum, L) to limestone applications were evaluated on several acid soils (Oxisols) of the Rio Grande do Sul plateau region, Brazil.;Seven field experiments were conducted during a five-year period to evaluate the efficiency of lime rate in relation to varying soil acidity conditions and time after lime applications.;Soil textural properties were related to the effect of lime treatments on the soil pH, on the exchangeable Ca + Mg content, and on CEC properties of the soils in this study. Maximum soil pH values occurred at higher values on the coarse textured soils than on the clay texture soils. A very high buffer capacity for pH changes was observed especially at high soil pH values. High soil pH values resulting from limestone rates applied to the soils reduced the exchangeable Al and Mn contents of the soils. Exchangeable Al was reduced to essentially zero values at an average soil pH 5.6, with a range of soil pH values between 5.2 to 5.8.;Maximum soybean yields around 3300 kg/ha were observed at soil pH 6.6 to 6.8, and marked yield limitations were observed below pH 5.5 or when exchangeable Al forms were present in the soil solution. Average soybean yield values between 1362 and 2959 kg/ha were observed for soil pH values ranging from 4.0 to 5.5.;Wheat grain yields were very variable, and this was associated with the occurrence of diseases which limited the analysis of data across years. Maximum average yields around 2467 kg/ha were observed at approximately soil pH 5.6, but yield reductions were observed at a soil Al content greater than 20% of the soil CEC and at soil pH above 6.0, which was associated with the occurrence of take-all (Ophiobulus sp.) disease.;Production functions were estimated through multiple linear regression techniques for individual crops and for the wheat and soybean aggregated crop system.;"Optimal" lime resource allocation was evaluated in relation to several factor/product price ratios, selected lengths of the production periods, several annual discounting rates, and diverse crop share alternatives.



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Otavio J. F. de Siqueira



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237 pages