著者

BACATIO C. D. KUBOTERA H. NANZYO M. YAMADA I.

出版者

東北大学

雑誌

Journal of integrated field science

巻号頁・発行日

vol.2, pp.19-27, 2005-03

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Intavas Techno Demo Farm is situated in high elevation of 1, 220 meters above sea level, with cool temperature and without pronounced dry season. The soil has low pH (5.24, average) and medium total carbon (4.3%) in the surface. Phosphorus retention is relatively high (77.5%, ave.), low cation exchange capacity (12 cmol(+) kg^<-1> ave.) and low base saturation (13%, ave.). Clay content is 45% (ave.) and bulk density of 1.1 Mg m^<-3> in average. Micrograph of the thin section of Bw_1 horizon reveals that void content is very small (6%). Voids are vughy and are not interconnected. In crossed nicol there were no clay illuviation seen. Total element analysis revealed that Intavas soils have about 60% Al_2O_3 but very low in SiO_2, 16.05% only. This indicates an advanced weathering that Si has been leached out and Al precipitated. As to the primary minerals, opaque minerals predominate with the presence of hornblende in heavy minerals. For light minerals, weathered particles predominate with the presence of mica, quartz and volcanic glass. Selective dissolution analysis reveals that Al_o is relatively high as compared to Fe_o and Si_o. However, these elements have the same pattern that irregularly decrease with depth and increase in the buried A horizon. Fe_p is relatively high followed by Al_p that significantly decreases with depth. The data show that amorphous materials are higher in surface and buried A horizons. Electron micrograph of BA shows no defined form that can be considered as amorphous materials. Bw_2 shows angular shapes that correspond to gibbsites and halloysite as indicated by spheroid configurations. X-ray diffraction pattern exhibits small and weak peak at 7 A in BA horizon. This peak corresponds to the presence of halloysite. The sharp and strong peaks at 4.8 A and 4.3 A in BA and Bw_2 horizons correspond to gibbsite. According to the selective dissolution analysis, electron microscopy and X-ray diffraction analysis, the dominant clay mineral in BA horizon is gibbsite and followed by amorphous material and small amount of halloysite. On the other hand, gibbsite dominate Bw_2 horizon followed by halloysite. Based on the physical, chemical, mineralogical and thin section analyses, the TDF soil can be classified as fine clayey, acid, isothermic, gibbsittic, Oxic Dystrudepts. It can be considered as soil with partial rejuvenation by volcanic ash material. As compared with soils without rejuvenation, this soil has higher total carbon, phosphorus retention, lower bulk density relatively, high amorphous materials in the surface and halloysite in the subsoils.Philippine soilsOxic Dystrudeptstephravolcanic glasshalloysitegibbsitedark and high humus surface