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Effect of Dehydration-Rehydration on Cation Exchange Capacity of Hawaiian Soils¹

ABSTRACT

Dehydration, induced by extended sun-drying or by short periods in an oven at 105° C., reduced the cation exchange capacity of a soil. This reduction generally increased with the annual rainfall, being most pronounced in the wettest soils of the Islands. Furthermore, in a given profile of these extremely wet soils, this reduction increased with depth. This trend is culminated in a subsoil of a Hydrol Humic Latosol (307% moisture) which dropped in capacity value from 125.8 me./100 g. to 37.6 me./100 g. in 100 days of sun-dehydration.

Removal of natural vegetative cover in a virgin area caused a reduction of 16.8% in cation exchange capacity for the surface soil at the end of 10 months in a Humic Latosol. Also, in this same area comparative figures for the virgin and cultivated surface soils show that extended cultivation with subsequent susceptibility to dehydration has caused a loss of 27.8% of the cation exchange capacity of the soil.

Soils which are located in dominantly dry areas showed a seasonal effect on cation exchange capacity. Samples taken after a rainy season showed slightly higher values than those taken during a dry season in a given site.

Dehydrated soils increased significantly in cation exchange capacity upon rehydration in dry and moderately wet area soils. This display of reversibility was not evident in wet area soils.

¹ Published with the approval of the Director of the University of Hawaii Agr. Exp. Sta. as Technical Paper No. 352.

² Junior Chemist, and Chemist, respectively, University of Hawaii Agr. Exp. Sta.

Received for publication July 14, 1955.