The characterization of marginal soils of three techno-demo farms in the Philippines

The morphological, physical, chemical and mineralogical properties of three typical marginal soils in the Philippines, which show poor productivity and are distributed in sloping to steep upland, hillyland and highland, were investigated at the Techno Demo Farms (TDF) established by the project of Environmental and Productivity Management of Marginal Soils in the Philippines. In Bulusukan TDF located in upland, the soil was fine loamy, smectitic, ishohyperthermic, Oxyaquic Vertic Haplustalf derived from alluvium. Its morphology and clay mineralogy, smectite, resembles to the Vertisols. Although this soil have, the problematic physical properties such as high bulk density and hardness, its chemical properties such as CEC, base saturation and pH are suitable for plant growth. In Agoho TDF in hillyland, the soil was very fine, kaolinitic, ishohyperthermic, Typic Hapludult derived from andesite and basalt. Its clay content was large, 70 to 83 %, and dominated by kaolin minerals. This soil is problematic for the agriculture in both physical properties such as hardness and clay accumulation that inhibits plant root growth and chemical properties such as extremely acidic pH and relatively high value of phosphate retention. Intavas TDF soil in highland, which was classified into fine loamy, gibbsitic, isothermic, Typic Haplohumults, showed unique properties. Although its parent rock is granodiorite, intermediate igneous rock, the SiO2 content was only 11 to 22 % reflecting the strong weathering. The dominant clay mineral was gibbsite accompanied by spheroidal halloysite and amorphous materials. The presence of amorphous clay and volcanic glass indicates the "partial rejuvenation by tephra materials" has occurred in this soil. Intavas soil has no problem in the physical properties, however chemical properties such as acidic pH and high phosphate retention should be improved.