Genesis and classification of brown forest soils derived from marl under natural vegetation

Genesis and classification of the soils derived from marl under natural vegetation and cultivated crop land in Kikai and Okinawa Islands were studied based on their physico-chemical and mineralogical properties. The results are as follows: 1) Under natural vegetation in Kikai Island, the soil derived from marl has A-Bwl-Bw2-BC-C horizon. The cambic B horizon is dull yellowish brown to yellowish brown (10YR5/3 or 2.5Y5/3) in color. medium subangular blocky structure. Soil reaction is slightly acid (pH5.1-6.2) and the degree of base saturation is 74-111%. The organic carbon content of A horizon is 40.4 g kg**-1 and decreases with depth. 2) Under natural vegetation in Okinawa Island (Yonabaru), the soil derived from marl has A-BA-Bw-BC-C horizon. The cambic B horizon is dark grayish yellow (2.5Y4/2) in color, medium subangular blocky structure. Soil reaction is slightly alkaline (pH8.0-8.5), the free carbonate is 58.3-85.8 g kg**-1. The organic carbon content decreases with depth (23.1-8.3 g kg**-1). 3) Under cultivated crop land in Okinawa Island (Kochinda), the soil derived from marl has A-ACg-Clg-C2-C3g horizon. The differentiation of horizon is not developed and its structure is massive except A horizon. 4) In Kikai and Yonabaru soil, the activity ratio of free iron oxides (Fe sub(o)/Fe sub(d)) ranges from 0.37 to 0.59, and the crystallinity ratio of free iron oxides [(Fe sub(d)-Fe sub(o))/Fe sub(t)]ranges from 0.12 to 0.24, while in Kochinda soil, they range from 0.16 to 0.25 and from 0.25 to 0.37, respectively. Under cultivated land, crystallization of amorphous free iron oxides proceeds more than under natural vegetation. 5) Soils under natural vegetation. Kikai and Yonabaru, are approximately correlated with Orthieutric Cambisol and Calcaric Cambisol in WRB, respectively. While in USDA Soil Taxonomy, both Kikai and Yonabaru soils are correlated with Typic Eutrudept On the other hand, the cultivated soil. Kochinda, is correlated with Calcaric Regosol in WRB or Typic Udorthent in USDA Soil Taxonomy.