Revista Brasileira de Ciência do Solo
On-line version ISSN 1806-9657
SILVA, Vladimir Antônio et al. Kinetics of K release from soils of Brazilian coffee regions: effect of organic acids. Rev. Bras. Ciênc. Solo [online]. 2008, vol.32, n.2, pp. 533-540. ISSN 1806-9657. http://dx.doi.org/10.1590/S0100-06832008000200008.
Kinetic studies on soil potassium release can contribute to a better understanding of K availability to plants. This study was conducted to evaluate K release rates from the whole soil, clay, silt, and sand fractions of B-horizon samples of a basalt-derived Oxisol and a sienite-derived Ultisol, both representative soils from coffee regions of Minas Gerais State, Brazil. Potassium was extracted from each fraction after eight different shaking time periods (0-665 h) with either 0.001 mol L-1 citrate or oxalate at a 1:10 solid:solution ratio. First-order, Elovich, zero-order, and parabolic diffusion equations were used to parameterize the time dependence of K release. For the Oxisol, the first-order equation fitted best to the experimental data of K release, with similar rates for all fractions and independent of the presence of citrate or oxalate in the extractant solution. For all studied Ultisol fractions, in which K release rates increased when extractions were performed with citrate solution, the Elovich model described K release kinetics most adequately. The highest potassium release rate of the Ultisol silt fraction was probably due to the transference of "non-exchangeable" K to the extractant solution, whereas in the Oxisol exchangeable potassium represented the main K source in all studied fractions.
Keywords : successive extractions; first order; zero order; parabolic diffusion; Elovich.