Kinetics and structural effects of the extraction of non‐exchangeable potassium from the clay fraction of soils of Galicia (N.W. Spain)

Abstract

The kinetics of non-exchangeable K extraction by the boiling HN03 and sodium tetraphenylborate (NaTPB) methods for the clay fractions of six typical soils of Galicia (N.W. Spain), whose predominant clay minerals are illites, vermiculites and illite-vermiculite intergrades, was investigated. The progressive structural degradation of the clay minerals during extraction was studied by X-ray diffraction. For the boiling HNO 3 method, extraction rate constants were significantly smaller for predominantly illite clays than for clays in which other micaceous minerals predominated. The X-ray diffraction data showed that even 60 minutes of the boiling nitric acid treatment was unable to expand the minerals widi 10A interlayer spacing, which invalidates this method for routine work. For extraction with NaTPB, there were no significant differences among the different types of clay regarding their extraction rate constants, but the X-ray data showed that illites were progressively expanded as extraction progressed. The theoretical models best fitting the K extraction data were in all cases the Elovich, power function and parabolic difussion equations, but the data were actually best fitted by a pair of straight line segments. The nearly 24 h mean time at which the two segments met for the NaTPB method suggests that extracting for this period of time would make the results of the NaTPB method more meaningful than the usual 72 h.

Kinetics of nonexchangeable‐potassium release and plant response in some calcareous soils

“…The two phases of K release were also reported by Gil-Sotres and Rubio (1992), Jalali (2005), Jardine and Sparks (1984), as well as by Sparks et al (1980). The release-rate constants (parabolic diffusion) obtained in this study were compared to those reported by other researchers.…”

“…A number of extractants have been used to study the release rate of nonexchangeable K from soils and clay minerals. These include dilute salt solutions (Dhillon et al, 1989), cation-exchange resins (Martin and Sparks, 1983), organic acids (OA) (Song and Huang, 1988), sodium tetraphenyl boron (Cox and Joern, 1997;Dhillon and Dhillon, 1992), nitric acid (Gil-Sotres and Rubio, 1992), and electro-ultrafiltration (EUF) technique (Rubio and Gil-Sotres, 1996). However, release of nonexchangeable K of soil in salt and OA solutions at low concentrations resembles the mechanism of plant-root extraction of K from soil particles.…”

Nonexchangeable potassium extraction and associated structural changes of mica dominant clay minerals

“…Substantial information is available on the nonexchangeable K release from soils differing in mineralogical composition, crop management conditions, and fertilization differences Sastry, 1993,1995;Paul et al, 1995;Majumdar et al, 1997;Pineiro and Garcia, 1997;Cox and Joern, 1997). However, the information on the associated structural alterations of clay minerals due to nonexchangeable K extraction is scanty (Gil-Sortres and Rubio, 1992;Datta and Sastry, 1995). The present investigation aims at studying the structural changes in clay minerals of some mica dominant soils as affected by the extraction of nonexchangeable K employing differential x-ray diffraction (DXRD) technique.…”