Anisotropy of Drainable Macropores in Andosols and Alluvial Soils

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1 J. Jpn. Soc. Soil Phys. No. 23, p.+/,.,**, * ** Anisotropy of Drainable Macropores in Andosols and Alluvial Soils Yukiyoshi IWATA* and Hajime NARIOKA** * National Agricultural Research Center for Hokkaido Region, Shinsei, Memuro-chou, Kasai-gun, Hokkaido *2, **1+, Japan ** Faculty of Environmental Science and Technology, Okayama University, Tsushima-naka, Okayama 1** 2/-*, Japan Abstract Since macropores significantly influence the movement of water and air in the soil, it seems that the 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 a model of entry pore structure, and found that this phenomenon is thought to reflect the shape of drainage 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 to have been greatly a#ected by the inner wall of the sampler. Nevertheless, it could be said that wall-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 shapes of 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 + X Bouma, +32+ ; +32. ; macropore X X +323 * *2, **1+ ** 1** 2/-* : X

2 16 23,**, Mori et al., +333 a, b ; +33/,***,*** a, b pf +.2 +, mm -** mm +** cm - +** cm -,,. + D / / +*,+ +/* cm /* cm + Fig. + Soil profiles of volcanic ash soil in upland field. +, X +** cm - - / X +** cm - -*.* mm ;X,AB, Bw,,.,,.,. + Gs ; ; w n r d,.,., Ks Ka Ks pf +.2 Tanner and Kirkham

3 : DIK-/**+ Ka Ks Ka Fig.,, Soil profiles of paddy field soil (alluvial soil).,., ,.,., cm cm - cm - cm - cm ; cm - cm - +33,,.,.. pf,.,. - pf +.* +.- pf +./ pf,.1 pf -.*..* pf,.,. / X -*.* mm ; X ; SOFTEX, DCTS-1**- 0* kv - ma FFD 0// mm +323 *.- mm *.- mm Table + Physical properties of soil sample,ab Bw, cm -/ 03 +*/ +,2 +2 -, -,.2 +0,3,3.- * HC CL L L LiC CL kg/kg +4, *4,, *4,1 *4,. *4,- g/cm - *4/. *4/2 +4., +4-, +4.* +4., cm - /cm - *42* *412 *4.1 *4/* *4.1 *4.1 cm - /cm - ** *4*1 *4+* *4*/ *4*. *4*- *4*/ * ** pf +.2

4 18 23,**, - Fig. - Hydraulic conductivity at saturated condition. Fig. / / Anisotropy of the entry-pore volume.. pf +.2 Fig.. Air permeability at pf +.2. Fig. 0 0 Anisotropy of the entry-pore pressure. +, +,,,, HC CL L LiC 1 Fig. 1 Anisotropy of the drain gradient.

5 : 19 Fig. 2 2 Bw, pf pf-moisture distribution curves of Bw, and ill-drained paddy field. -., -. Ks +* - cm s +*. +* 0 cm s Ks pf +.2 Ks Ks Ks Ka -. - / 1 +32/ ; +323,AB Bw, -.. pf Bw, pf 2 Bw, pf / pf +.* +.- pf +./ +.2 pf pf 2.., -. / X 3 +, X

6 ! " 23 #,**, 20 ῌ3ῌ+, Figs. 3ῌ+, X Soft X-ray radiographs of tubular-pore (macropore) of upland field (volcanic ash soil) and paddy field. ῌ3,AB -/ 03 cm Fig. 3 Volcanic ash soil,,ab layer (-/ῌ03 cm depth), Film No. N30,/3. ῌ+* Bw, +*/ +,2 cm Fig. +* Volcanic ash soil, Bw, layer (+*/ῌ+,2 cm depth), Film No. N30,-1. ῌ++ +0,3 cm Fig. ++ Ill-drained paddy field, plowsole (+0ῌ,3 cm depth), Film No. N3/,0/. ῌ+,,3 cm Fig. +, Ill-drained paddy field, subsoil (,3cm depth), Film No. N3/,03.

7 : 21 Fig Soil structure model of the entry-pore in each soil types. +* +* +323 *.- mm,ab Bw, Bw,,AB /... + Bw, , ,AB,AB +- : : : X,AB Bw,,AB,AB,* cm *.+/ mm,ab,ab 3 *.+/ *.- mm

8 22 23,**, Bw,,AB.. +., *.- mm,ab X ++ +, *.- mm +- : : : +. Fig. +..., +**cm - pf +3/, pf pf +323 pf pf pf +** cm - 2 pf pf,ab Bw, pf Soil structure of samples which have anisotropy in pf-distribution curve. pf pf +.

9 : 23 pf X +, *.+ *., mm pf pf / *.+* *.+/ mm X pf pf +** cm - pf.. - +** cm - +31* ;,*** +** cm - +** cm - X +* +/ Fig. +/ E#ect of sampler-wall to drainage experiment. +/.. +.., pf +** cm - +/

10 24 23,**, +** cm - / +** cm - X +** cm - pf Bouma, J (+32+) : Comment on Micro-, Meso-, and Macroporosity of Soil. Soil Sci. Soc. Am. J.,./ : +,.. +,./ : p.,1,,*** :,*3 : : /. :.3* * :.+ : ++3 +,* +3/, : B, : 31 +,, Mori, Y., Iwama, K., Maruyama, T. and Mitsuno, T. (+333 a) : Discriminating the Influence of Soil Texture and Management-Induced Changes in Macropore Flow Using Soft X-Rays. Soil Science, +0. :.01.2,. Mori,Y., Maruyama, T. and Mitsuno, T. (+333 b) : Soft X-ray Radiography of Drainage Patterns of Structured Soils. Soil. Soc. Am. J., 0- : * : + : + /0 +33, :. : -/ : 0. : 3* 31,*** :,*2 : 0-1+,*** a :,*2 : 33 +*/,*** b :,+* : +3,1 +33/ :,+ : : 1 : -, : X ++. : / : /+ :.3 0, :,**+,,- :,**+ +, +-

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