EFFECTS OF ADSORBED CATIONS ON PHYSICAL PROPERTIES OF TROPICAL RED EARTHS AND TROPICAL BLACK EARTHS .I. PLASTIC LIMIT, PERCENTAGE STABLE AGGREGATES, AND HYDRAULIC CONDUCTIVITY

Similar relative effects were obtained for plastic limits, percentage stable aggregates, and hydraulic conductivities when a tropical red earth, consisting predominantly of kaolin and iron oxide, and a tropical black earth consisting predominantly of montmorillonite, were saturated with Ca, Mg, K, or Na ions or combinations of these. Plastic limits were independent of the nature of the saturation cations, but were significantly dependent upon clay type. Percentage stable aggregates of artificially prepared aggregates and hydraulic conductivity were affected by the four cations in the order Ca = Mg > K Na and were also significantly affected by clay type. Combinations of the four cations generally gave intermediate effects with Ca‐saturated soils more susceptible to deterioration by K or Na than Mg‐saturated soils. The results confirm the generally deleterious effect of Na ions and show that K ions have effects similar to Na on the properties investigated. They suggest that heavy potash fertilization without liming may lead to structural deterioration of these soils. Copyright © 1969, Wiley Blackwell. All rights reserved