AbstractsEarth & Environmental Science

Typescript. Bibliography: leaves 103-105a. [4], vi, 115 l illus. (part col., mounted), tables Morphological, physical, chemical, and mineralogical properties of six Black Earth profiles from the island of Oahu, Hawaii were studied. 1he probable source of the dark color was also investigated. The properties of these soils were compared with those of the Black Earths in other countries. The soils were classified by the new V.S.D.A. Comprehensive Soil Classification System. Dark color, heavy clay texture, granular mulch, and slickensides on the surfaces of parallelepipeds were characteristic of most of the profiles. Hence, they are similar to other Black Earths in morphology. The silt contents and bulk density values shown by the profiles were lower than other Black Earths. The clay contents and, subsequently, the moisture retention at saturation, at moisture equivalent, and at 15 atmospheres were higher. The pH values of the Hawaii Black Earths were similar to those from other countries but the ΔpH values were much higher. Calcium and magnesium status was high. Exchangeable calcium was similar in range and magnitude to other Black Earths, but the exchangeable magnesium was In the higher extreme of the range of this particular group of soils. Organic matter levels, exchangeable sodium and potassium, and cation-exchange-capacity values were comparable to other Black Earths. Total SiO2 and total Fe2O3 levels suggested that one of the profiles was perhaps a Black Earth intergrade to Red Earths. Montmorillonitic clay was dominant. Kaolinite and halloysite were also components of the colloidal clay fractions. Feldspars dominated the sand fractions, while magnetite, ilmenite, and hematite occupied the greater bulk of the silt fractions. The magnetic opaque minerals in the silt and sand fractions were perhaps the main contributor to the dark color of the soils. Classification of the soils according to the categories prescribed by the 7th Approximation was not very satisfactory. A modification of the scheme using the same principles was proposed.