ニュージーランド火山灰土の特徴と腐植組成

抄録

Characteristics and humus composition of several soils derived from volcanic ash deposits were studied. These soils were Red/Brown loam (R/BL), Yellow-brown loam (YBL), Yellow-brown pumice soil (YBP) and Recent soil from volcanic ash (RSVA), classified according to the New Zealand Soil Classification System. Samples were taken from the four volcanic regions in the North Island. The main findings are as follows : 1) The carbon content of the topsoil in the older volcanic ash soils (R/BLs and YBLs) generally exceeded 10%, while that of the younger YBPs was usually less than 7%. 2) The Phosphate absorption coefficient of R/BLs and YBLs was generally higher than that of the YBPs and RSVAs. 3) The base saturation percentage of RSVAs was considerably higher than that of the other volcanic ash soils. 4) Humic acids in YBPs were usually the B-type with the A-type as a mi- nority, while those in YBLs were dominantly of the P-type. Most P-type humic acids in YBLs exhibit P_<++> and P_<+++> type features. 5) The Ch : Cf ratios of RSVAs and YBPs were higher than those of YBLs and R/BLs, in general. 6) According to the present study, the humus content and the degree of humification in New Zealand volcanic ash soils were generally lower than those of ordinary Japanese "Kurobokudo" (volcanic ash soils).