Cinética de liberação do potássio em solos de regiões cafeeiras: efeito de ácidos orgânicos
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2000
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Resumo
Estudos de cinética de liberação de K podem contribuir para a avaliação da sua disponibilidade no solo para as plantas. Este trabalho teve como objetivos investigar a cinética de liberação do potássio nas frações terra fina, areia, silte e argila de dois solos do estado de Minas Gerais, Brasil, originalmente cultivados com cafeeiro e comparar quatro equações para descrevê-la. As frações foram submetidas a oito extrações sucessivas (0 a 665h) com citrato e oxalato 10-3 mol L-1 sendo os resultados de K liberado somados e plotados em função do tempo. Foram comparadas as equações de ordem zero, primeira ordem, Elovich e
parabólica de difusão para verificar qual delas melhor descreve a cinética de liberação do K. Na condução do experimento utilizaram-se amostras do horizonte B de um Latossolo Roxo (LR) originado de basalto e uma Terra Bruna Estruturada (TB) originada de sienito nefelínico. Para cada equação foram calculados o coeficiente de correlação (r) e o erro padrão da estimativa (EP). A equação de primeira ordem descreveu melhor os resultados do LR e a equação de Elovich se ajustou melhor aos resultados da TB. As velocidades de liberação do K para o LR foram semelhantes em todas as frações estudadas e não foi observado efeito dos ácidos orgânicos na velocidade de liberação do K porque a maior parte dele era proveniente da forma trocável. Na TB, o citrato acelerou a liberação do K em todas as frações estudadas, tendo a fração silte apresentado maior velocidade, porque a maior parte do K proveniente dela estava na forma trocável.
Kinetics studies on the release of potassium from soils can contribute to a better understanding of K availability to plants. This study was conducted to evaluate the kinetics of K release from different soil fractions (whole soil, clay, silt, and sand) of B-horizon samples of a Dusky-Red Latosol (DR, which is a basalt-derived Oxisol) and a Structured-Brown-Earth Soil (SBE, which is a sienite-derived Ultisol), both representative soils from coffee regions of Minas Gerais State, Brazil. Potassium release from each soil fraction was measured by eight successive extractions (0 - 665h) with 10-3 mol L-1 of either citrate or oxalate. First-order, Elovich, zero-order, and parabolic diffusion equations were used to check for the best fit, which was done by correlation as well as least-squares analyses. The kinetics of K release in the DR soil was best described by the first-order equation, whereas the Elovich equation gave the best fit in the SBE soil. All soil fractions of the DR soil behave the same way as for the rate of K release. There were no effect of either citrate or oxalate on the kinetics of K release from the DR soil, which had most of its K supply coming from the exchangeable form. Citrate caused an increase in the rate of K release from the SBE soil. In such soil, the highest rate was observed for the silt fraction, probably because most of its K was in the "exchangeable" form.
Kinetics studies on the release of potassium from soils can contribute to a better understanding of K availability to plants. This study was conducted to evaluate the kinetics of K release from different soil fractions (whole soil, clay, silt, and sand) of B-horizon samples of a Dusky-Red Latosol (DR, which is a basalt-derived Oxisol) and a Structured-Brown-Earth Soil (SBE, which is a sienite-derived Ultisol), both representative soils from coffee regions of Minas Gerais State, Brazil. Potassium release from each soil fraction was measured by eight successive extractions (0 - 665h) with 10-3 mol L-1 of either citrate or oxalate. First-order, Elovich, zero-order, and parabolic diffusion equations were used to check for the best fit, which was done by correlation as well as least-squares analyses. The kinetics of K release in the DR soil was best described by the first-order equation, whereas the Elovich equation gave the best fit in the SBE soil. All soil fractions of the DR soil behave the same way as for the rate of K release. There were no effect of either citrate or oxalate on the kinetics of K release from the DR soil, which had most of its K supply coming from the exchangeable form. Citrate caused an increase in the rate of K release from the SBE soil. In such soil, the highest rate was observed for the silt fraction, probably because most of its K was in the "exchangeable" form.
Descrição
Trabalho apresentado no Simpósio de Pesquisa dos Cafés do Brasil (1.: 2000 : Poços de Caldas, MG). Resumos expandidos. Brasília, D.F. : Embrapa Café; Belo Horizonte : Minasplan, 2000. 2v. (1490p.) : il.
Palavras-chave
Café Potássio Ácidos orgânicos, Coffe Potassium Organic acids
Citação
Silva, Vladimir Antônio; Nogueira, Francisco Dias; Guimarães, Paulo Tácito Gontijo; Guilherme, Luiz Roberto Guimarães. Cinética de liberação do potássio em solos de regiões cafeeiras: efeito de ácidos orgânicos. In: Simpósio de Pesquisa dos Cafés do Brasil (1.: 2000 : Poços de Caldas, MG). Resumos expandidos. Brasília, D.F. : Embrapa Café; Belo Horizonte : Minasplan, 2000. 2v. (1490p.), p. 1408-1411.