
J. Jpn. Soc. Soil Phys.
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No. 23, p. +/,. ,**,

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*ῌ **
Anisotropy of Drainable Macropores in Andosolsand Alluvial Soils
Yukiyoshi IWATA* and Hajime NARIOKA*** National Agricultural Research Center for Hokkaido Region,
Shinsei, Memuro-chou, Kasai-gun, Hokkaido *2,ῌ**1+, Japan** Faculty of Environmental Science and Technology, Okayama University,-ῌ+ῌ+ Tsushima-naka, Okayama 1**ῌ2/-*, Japan
Abstract
Since macropores signiﬁcantly inﬂuence the movement of water and air in the soil, it seems thatthe structure of macropores should determine the processes of drainage.

A study was conducted

to investigate the structure of macropores and the associated drainage process.

The drainage

characteristics of volcanic ash and paddy ﬁeld soils were investigated, and the following results
were obtained.
(i) The structure of entry pores depended on the direction of sampling. We constructed amodel of entry pore structure, and found that this phenomenon is thought to reﬂect the shape ofdrainage macropores, especially the joints of tubular pores that have di#erent diameters.
(ii) The results of drainage experiments using a +** cm- cylindrical sampler were thought tohave been greatly a#ected by the inner wall of the sampler.

Nevertheless, it could be said thatwall-a#ected results show soil drainage characteristics better than non-wall-a#ected results.

We

constructed a model of drainable macropores structure to explain this phenomenon. The shapesof pF-distribution curves were di#erent depending on the direction of sampling when soil was
sampled using a +** cm- cylindrical sampler.

This could be explained by assuming that large

tubular pores in the network of macropores were in a vertical direction and smaller tubular pores
were in a horizontal direction.
Key words : macropore structure, drainability, anisotropy, soft X-ray imaging method, sampling
scale

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Soil proﬁles of volcanic ash soil in
upland ﬁeld.

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Soil proﬁles of paddy ﬁeld soil (alluvialsoil).

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Hydraulic conductivity at saturated
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Anisotropy of the entry-pore volume.

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Air permeability at pF +.2.

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19

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Fig. 2

pF-moisture distribution curves of Bw, and ill-drained paddy ﬁeld.

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20

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Figs. 3ῌ+,  X 

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ash soil) and paddy ﬁeld.

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Fig. 3

Volcanic ash soil, ,AB layer (-/ῌ03 cm depth), Film No. N30,/3.

Fig. +*

Volcanic ash soil, Bw, layer (+*/ῌ+,2 cm depth), Film No. N30,-1.

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Fig. ++

Ill-drained paddy ﬁeld, plowsole (+0ῌ,3 cm depth), Film No. N3/,0/.

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Fig. +,

Ill-drained paddy ﬁeld, subsoil (῍,3cm depth), Film No. N3/,03.

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Fig. +-

Soil structure model of the entry-porein each soil types.

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Fig. +/

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./01234$5%6  +7 (+333 a) : Discriminating the Inﬂuence of Soil

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Texture and Management-Induced Changes in/ῌ ῍ ῐ ῏ ῎Macropore Flow Using Soft X-Rays. Soil Science,+0. : .01ῌ.2,.

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