Potassium release and fixation in Ferralsols (Oxisols) from Southern Togo

Abstract

ORSTOM U R 2B c/o DPVE, *CEA, DPVE, CEN Cadarache, 13 108 Saint Paul 16s Durance, France, f CIRADjIRAT, BP 1163, Lomk, Togo and SORSTOM UR ID, 70 route d'Aulnay, 93 143 Bondy cedex, France S U M M A R YPotassium release and fixation were studied on Ferralsols (typic Eutrustox) of Southern Togo both by isotopic exchange with 42K+ ions and by exchange with 1 M ammonium acetate. Experiments were conducted on soil samples taken from surface (0-30 cm) and subsoil (80-100 cm) layers of four plots. These plats, with the same soil type, were subjected to various kinds of use: forest and crops, with or without fertilizers. A single wetting and drying of the soil samples increased the amounts of exchangeable K. This exchangeable K release could stem from clay protonation during drying. However, the K release is insufficient to allow permanent intensive agriculture without K fertilizer addition. Soil samples were therefore treated with KCI in order to study K fixation. About 20% of the applied K was fixed and the percentage increased with wetting and drying. The fixation can be explained by the presence of about 2% of interstratified clay minerals in these kaolinitic soils. Comparison of the kinetic characteristics of the isotopically exchangeable K with the amounts of ammonium exchangeable K revealed the existence of several kinds of exchange site for K ions.

Characteristics of soil exchangeable potassium according to soil color and landscape in Ferralsols environment

“…The sensitivity of soil color to wetness (Poss et al, 1991) and the change of soil physic and chemical characteristics (Vizier, 1971) as observed for soil content of K (Koné et al, 2009d), are further supporting current finding and relevant assertions.…”

Which 2:1 clay minerals are involved in the soil potassium reservoir? Insights from potassium addition or removal experiments on three temperate grassland soil clay assemblages

“…The behavior of the smectite layers of interstratified kaolinite/smectite clay minerals described in some tropical areas will also deserve some further investigation. Some studies (Delvaux et al, 1990;Poss et al, 1991) revealed that such layers, even in subsidiary quantities, could be a major source of K for the surrounding vegetation. The possible modifications of X-ray patterns of interstratified kaolinite/smectite following K absorption or removal remain at the moment an open question.…”

Clay minerals as a soil potassium reservoir: observation and quantification through X-ray diffraction

“…Indeed, several studies showed that the presence of such clay minerals, even in subsidiary quantities, increases effective soil K availability (e.g. Arkcoll et al 1985;Delvaux et al 1990;Poss et al 1991). The particular importance of such clay layers relies on their ability to adsorb and release K + ions from 2:1 clay mineral interlayer sites (e.g.…”