Cationic equilibria in selected soils and soil materials

Abstract

The relationship between exchangeable potassium and ARKe was studied for four agronomically-important soils of the O.F.S. Region and two commercial clays. Some attention was also given to the Q/I and Gapon relationships for these soils and claysc The effects of some factors, e.g. sodium level and clay:solution ratio, on these parameters were also investigatedo Linear relationships between Kex and ARKe were found for all soils and clays used. In most cases the graphs relating Kex to ARKe had intercepts different from zeroo At extremely high levels of K saturation in bentonite the slopes of the graphs changed and different linear relationships were obtained, the slopes of the upper portions being lower than those of the lower portions. At high Kex levels a fairly good numerical similarity between -∆K and Kex was found in most caseso At Kex level near EK , i.e. that level of Kex where ARKe becomes zero, -∆KO decreased relative to Kex. At these low Kex levels -∆KO was therefore not a good indication of Kex. PBCK proved to be a very constant property of a soil or clay, being unaffected by most experimental conditions and by level of K saturation. The PBCK values of these soils were very lowo PBCK of bentonite was strongly influenced by clay: solution ratio when ∆K values were expressed as me per 100g clay. Increased sodium levels changed the relationships between Kex and ARKe, but did not cause poorer relationships between these two parameters. The magnitude of the effect of sodium was a function of the amount of sodium brought into the system and the latter was largely a function of the CEC of a soil.