A cultura do café no Brasil tem apresentado frequente deficiência de magnésio (Mg) limitando sua produtividade, portanto faz-se necessário o estudo de fontes que contenham Mg para essa cultura. Por outro lado, o estudo das metodologias de análise de K, Ca e Mg no solo é um outro ponto que precisa ser estudado para melhor manejo da fertilidade do solo e recomendação de adubações. Objetivou-se com o primeiro experimento avaliar a eficiência de fontes de magnésio para a cultura do café e a dinâmica deste nutriente no perfil do solo. E com o experimento desenvolvido em Arkansas-EUA, avaliar as correlações entre as concentrações de nutrientes do solo seco em estufa e úmido de campo extraídos com Mehlich-3 e 1 mol L-1 NH4OAc. Observou-se que o óxido e oxissulfato de Mg elevaram os valores de pH e CTC e diminuíram a concentração de H + Al do solo. As fontes diminuíram a disponibilidade de K e Ca, e aumentaram o Mg no solo. Na planta, óxido e sulfato de Mg proporcionaram maior concentração de Mg foliar. Apenas no segundo ano de avaliação houve aumento de produtividade do café. Os fertilizantes óxido e oxissulfato de Mg obtiveram o maior índice de eficiência agronômica em relação ao carbonato de Mg. No segundo experimento, K, Ca e Mg extraíveis com Mehlich-3 e NH4OAc foram altamente correlacionados (r2> 0,95) tanto para solo úmido de campo quanto para o seco em estufa. A relação entre as concentrações de K no solo seco em estufa e úmido de campo para Mehlich-3 e NH4OAc foram muito semelhantes e altamente correlacionados (r2 = 0,92). A secagem do solo em estufa teve efeito mínimo sobre as concentrações de Ca e reduziu a concentração de Mg tanto para Mehlich-3 quanto para NH4OAc. Entre os nutrientes estudados, a concentração de K foi a mais afetada pela secagem em estufa, necessitando de pesquisas de campo para correlacionar e calibrar novas recomendações agronômicas. / Brazilian coffee crop has often presented magnesium (Mg) deficiency limiting its productivity, so it is necessary to study sources containing Mg for this crop. On the other hand, the study of K, Ca and Mg soil analysis methodologies are another point that needs to be study to better management of soil fertility and fertilizer recommendation. The purpose of the first experiment was to evaluate Mg sources efficiency for coffee crop and nutrient dynamics in the soil profile. The second experiment objective, developed in Arkansas-US, was to evaluate the correlation between field-moist and oven-dry soil nutrient concentrations extracted with Mehlich- 3 and 1 mol L-1 NH4OAc. It was observed that the oxide and Mg oxysulfate increased pH and CEC values and decreased H + Al concentration. Mg sources declined K and Ca availability, and increased soil Mg. In the plant, oxide and Mg sulfate provided higher leaf Mg. Only in the second year there was increase coffee productivity. Oxide and Mg oxysulfate fertilizers had the highest agronomic efficiency index relative to Mg carbonate. In the second experiment, Mehlich-3 and NH4OAc extractable K, Ca, and Mg concentrations were highly correlated (r2 > 0.95) for both field-moist and oven-dry soil. The relation between oven-dry and field-moist K concentrations for Mehlich-3 and NH4OAc was very similar and highly correlated (r2 = 0.92). Oven drying had minimal effect on Ca concentrations and decreased Mg concentrations for both Mehlich-3 and NH4OAc. Among the Mehlich-3 extractable nutrients that are used to make fertilization decisions, K concentration was most affected by ovendrying and requires field research to correlate and calibrate new agronomic recommendations.

A cultura do café no Brasil tem apresentado frequente deficiência de magnésio (Mg) limitando sua produtividade, portanto faz-se necessário o estudo de fontes que contenham Mg para essa cultura. Por outro lado, o estudo das metodologias de análise de K, Ca e Mg no solo é um outro ponto que precisa ser estudado para melhor manejo da fertilidade do solo e recomendação de adubações. Objetivou-se com o primeiro experimento avaliar a eficiência de fontes de magnésio para a cultura do café e a dinâmica deste nutriente no perfil do solo. E com o experimento desenvolvido em Arkansas-EUA, avaliar as correlações entre as concentrações de nutrientes do solo seco em estufa e úmido de campo extraídos com Mehlich-3 e 1 mol L-1 NH4OAc. Observou-se que o óxido e oxissulfato de Mg elevaram os valores de pH e CTC e diminuíram a concentração de H + Al do solo. As fontes diminuíram a disponibilidade de K e Ca, e aumentaram o Mg no solo. Na planta, óxido e sulfato de Mg proporcionaram maior concentração de Mg foliar. Apenas no segundo ano de avaliação houve aumento de produtividade do café. Os fertilizantes óxido e oxissulfato de Mg obtiveram o maior índice de eficiência agronômica em relação ao carbonato de Mg. No segundo experimento, K, Ca e Mg extraíveis com Mehlich-3 e NH4OAc foram altamente correlacionados (r2> 0,95) tanto para solo úmido de campo quanto para o seco em estufa. A relação entre as concentrações de K no solo seco em estufa e úmido de campo para Mehlich-3 e NH4OAc foram muito semelhantes e altamente correlacionados (r2 = 0,92). A secagem do solo em estufa teve efeito mínimo sobre as concentrações de Ca e reduziu a concentração de Mg tanto para Mehlich-3 quanto para NH4OAc. Entre os nutrientes estudados, a concentração de K foi a mais afetada pela secagem em estufa, necessitando de pesquisas de campo para correlacionar e calibrar novas recomendações agronômicas. / Brazilian coffee crop has often presented magnesium (Mg) deficiency limiting its productivity, so it is necessary to study sources containing Mg for this crop. On the other hand, the study of K, Ca and Mg soil analysis methodologies are another point that needs to be study to better management of soil fertility and fertilizer recommendation. The purpose of the first experiment was to evaluate Mg sources efficiency for coffee crop and nutrient dynamics in the soil profile. The second experiment objective, developed in Arkansas-US, was to evaluate the correlation between field-moist and oven-dry soil nutrient concentrations extracted with Mehlich- 3 and 1 mol L-1 NH4OAc. It was observed that the oxide and Mg oxysulfate increased pH and CEC values and decreased H + Al concentration. Mg sources declined K and Ca availability, and increased soil Mg. In the plant, oxide and Mg sulfate provided higher leaf Mg. Only in the second year there was increase coffee productivity. Oxide and Mg oxysulfate fertilizers had the highest agronomic efficiency index relative to Mg carbonate. In the second experiment, Mehlich-3 and NH4OAc extractable K, Ca, and Mg concentrations were highly correlated (r2 > 0.95) for both field-moist and oven-dry soil. The relation between oven-dry and field-moist K concentrations for Mehlich-3 and NH4OAc was very similar and highly correlated (r2 = 0.92). Oven drying had minimal effect on Ca concentrations and decreased Mg concentrations for both Mehlich-3 and NH4OAc. Among the Mehlich-3 extractable nutrients that are used to make fertilization decisions, K concentration was most affected by ovendrying and requires field research to correlate and calibrate new agronomic recommendations.

From the Proceedings of the 1971 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 22-23, 1971, Tempe, Arizona / A study was made to determine how the evaporation rate from a bare Adelanto loam soil in Phoenix changes with season and with time since the last irrigation. The evaporation rates were determined by precision lysimeters in a bare field, with measurements being taken in every month of the year for at least a week after irrigation. The data exhibited a cosine-shaped curve, with a maximum evaporation rate of about 5 mm/day in summer and a minimum rate of about 2 mm/day in winter. By the seventh day, seasonal effects virtually disappear, and the evaporation rate is the same in both summer and winter, being about 2 mm/day after the 7th day and about 0.75 mm/day after the 21st day. It is generally accepted that soil dries in 3 stages, and the transition between the 1st and 2nd stages occurs when atmospheric conditions are no longer critical. In previous laboratory studies of soil drying, with constant atmospheric conditions, stage 1 was easily distinguished from stage II, and these results correlated closely with the equations of Gardner and Hillel. The individual drying curves of this field study were qualitatively different from the laboratory studies and did not confirm the predictions of the equations, suggesting that diurnal variations in temperature and other meteorological parameters have caused the difference.

From the Proceedings of the 1974 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 19-20, 1974, Flagstaff, Arizona / Reliable information on soil-water status is required in order to make accurate water balance studies of watersheds, to determine the survival probabilities of various types of vegetation between rainfalls in low rainfall areas, and to determine the susceptibility of the uppermost soil to wind erosion. Simple solarimeters may help to accomplish this objective. Bare soil albedo was a linear function of the water content of a very thin surface layer of soil, and albedo correlated well with water contents of thicker soil layers. In addition, albedo measurements could be used to delineate the 3 classical stages of soil drying. Albedo may also be used to differentiate between the initial potential rate phase of evaporation following an application of water, and the succeeding falling rate phase. Results of applying this technique to a field of Avondale clay loam indicate that 20% to 25% of the water applied by either irrigation or rain will be lost by stage 1 potential evaporation, independent of seasonal variations in evaporative demand. Presently the techniques developed are applicable only to bare soil surfaces.