Abbreviations: AL-7, alpine biome; Al d , citrate-dithionite-extractable aluminum; Al o , oxalate-extractable aluminum; Al p , pyrophospate-extractable aluminum; BO-1, blue oak biome; Fe d , citrate-dithionite extractable iron; Fe o , oxalate-extractable iron; PO-2, pine-oak biome; PP-3, ponderosa pine biome; RF-5, red fi r biome; SA-6, subalpine biome; Si o , oxalate-extractable silicon; SRO, short-range ordered; WF-4, white fi r biome; XRD, x-ray diffraction.

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The acidification of allophanic Andosols by fertilizer application in relation to soil productivity was studied with special reference to the soil colloidal composition. Among the Japanese cultivated allophanic Andosols, in 95% of the samples, the exchange acidity y1 was < 6, while in 5% of the samples (30 soil samples) the exchange acidity y1 was ≧ 6. The strongly acidic allophanic Andosols (exchange acidity y1≧ 6) did not significantly differ from the weakly acidic allophanic Andosols in the contents of amorphous materials. However, the mean values of the strongly acidic allophanic Andosols for the soil pH and base saturation which were 4.5 ± 0.3 and 15 ± 9%, respectively, were relatively lower than those of weakly acidic allophanic Andosols. The content of KCl‐extractable Si in the strongly acidic allophanic Andosols dominated by allophane (exchange acidity y1≧ 6 and allophane/clay content ratio > 0.7) ranged from 51 to 141 mg kg−1, and the values increased with increasing concentrations of KCl‐extractable Al. KCl‐extractable Al in the cultivated allophanic Andosols was considered to be derived from both the allophane fraction and Al‐humus complexes. In the field studies of allophanic Andosols with successive application of fertilizers conducted at the Fujisaka Branch of Aomori Agricultural Experiment Station, the value of the exchange acidity y1 of the topsoil and subsoil exceeded 6 about 40 and 50 years after the start of the experiment, respectively. The yield of flint corn (Zea mays L. var. indurata Bailey. cv. Onoa) in the fertilizer plot decreased by the strong soil acidification. The amount of nitrogen mineralized in the soil of the fertilizer plot during a 280‐d incubation was 0.114 g kg−1 in the topsoil and 0.041 g kg−1 in the subsoil. These values were relatively low compared with those in the lime + fertilizer plot. Thus, we confirmed that the subsoil fertility of the fertilizer plot decreased by heavy application of fertilizers.

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Path Analysis of Phosphorus Retention Capacity in Allophanic and Non-allophanic AndisolsSoil Chemistry P hosphorus retention capacity is an important property controlling the release of P from soil to surface water. Phosphorus retention in acidic soils is primarily regulated by Al and Fe in clay minerals (Kang et al., 2009;Zhang et al., 2005). Both Al and Fe minerals are abundant in volcanic ash soils that are characterized by a high PRC (Shoji and Ono, 1978;Wada and Gunjigake, 1979). To understand P retention behavior in soils, the chemical fractionation of Al and Fe is more critical than the total amount existing in the soil. Hiradate and Uchida (2004) grouped the chemical forms of Al and Fe into (i) humus complexes, (ii) non-and poorly crystalline metal hydroxides (e.g., allophane and ferrihydrite), (iii) crystalline metal (hydr)oxides (e.g., gibbsite and goethite), and (iv) stable minerals (e.g., phyllosilicates). Non-and poorly crystalline Al and Fe hydroxides, which can selectively be extracted by acid ammonium oxalate solution (Al ox and Fe ox ), are known to be the major P sorbent in noncalcareous soils (McKeague and Day, 1966;Schoumans, 2000). Th e fractions of Al p and Fe p represent metal-humus

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