深さ1m以上の泥炭土からなり,約10cmの客土がなされた造成3年後と16年後の草地圃場(3年圃場と16年圃場)で,客土層直下の泥炭層(O1層)およびその下部の泥炭層(O2層)の物理性と組織構造を調査した。1)両圃場の表層約25cmを占めるO1層およびO2層の主要な構城植物は,ホロムイスゲ(Carex middendorffii Fr.Schm)で,そのvon Post法分解度は3年圃場でH2〜H3,16年圃場でH6であり,造成後の経過年数の長い圃場で分解・変質が進んだ。2)3年圃場O1層の水平方向の組織構造では植生の組織全体が押し潰された状態で認められるが,16年圃場では,シュロ毛状の繊維が多く,中に黒く光沢のある物質が認められた。3年圃場の垂直方向の組織構造では紙を重ねたような累層状態が認められるが,16年圃場では累層状態が明瞭でなく,黒く光沢のある物質が点在した。3)3年圃場のO1層の容積重は0.14gcm^<-3>であるが,16年圃場では約1.5倍の0.22gcm^<-3>に,固相率は0.05cm^3cm^<-3>から約2倍の0.11cm^3cm^<-3>に,難有効水分孔隙(pF:3.0-4.2)量は0.08cm^3cm^<-3>から約2倍に増加したが,易有効水分孔隙(pF:1.8-3.0)量は0.38cm^3cm^<-3>からほぼ半減した。4)両圃場のO1層の強熱減量は約0.85gg^<-1>であった。16年圃場のO1層の繊維含量は3年圃場のO1層よりも明らかに少く,繊維の分解を示し,von Post法での分解度が大きいことと一致した。5)調査時の16年圃場の土壌水分張力は3年圃場よりも高く,乾燥していた。6)以上のことは,O1層では造成後,泥炭が脱水収縮だけでなく,分解・変質も進行したことを示した。

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The effect of tillage pan formation on the growth of sugar beet was studied in the fine-textured Brown lowland soils with texture of SiC or SiCL. Chemical and physical properties of soils, soil water potential and sugar beet root distribution in the early, middle and latter growth periods were measured for each soil type of fine-textured Brown lowland soil with texture of SiC or SiCL, medium-textured Brown lowland soil, Andosol and Wet Andosol. Physical properties of soils were favorable in the order of medium-textured Brown lowland soil, Andosol, Wet Andosol and fine-textured Brown lowland soil. On the other hand, chemical properties of soils were favorable in the order of fine-textured Brown lowland soil, medium-textured Brown lowland soil, Andosol and Wet Andosol. It was clarified from the changes in soil water potential and percentage of gaseous phase that the movement of soil water in the fine-textured Brown lowland soil was controlled to a larger extent by the percentage of the pore filled with gravitational water than that in the other soils. Therefore, the decrease in the percentage of pore filled with gravitational water due to the formation of tillage pan is considered to influence to the deterioration of drainage and to the restriction of water uptake by the crop root. Root penetration in the early growth period showed no significant difference among soil types, where the root was distributed in the plowed layer. In the middle growth period, the root penetrated to the plowed layer and middle layer in the fine-textured Brown lowland soil. In the other soils, the root was distributed below the middle layer. In the latter growth period the root in the fine-textured Brown lowland soil penetrated below the middle layer. The growth and yield of sugar beet were the worst defective in the fine-textured Brown lowland soil. The growth in the middle growth period influenced the growth in the latter growth period. It is considered that, in fine-textured Brown lowland soil, soil water environment was deteriorated and the root penatrartion was restricted due to the formation of tillage pan. Therefore, the water uptake by root was suppressed until the middle growth period due to the deteriorated soil water condition. As a result, it is considered that the formation of tillage pan is responsible for the inferior growth and yield of sugar beet in the fine-textured Brown lowland soil.

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We investigated several properties of water-stable soil aggregates giving special attention to macroaggregation (>0.25 mm), using 3 volcanic (group A) and 3 non-volcanic (group B) ash soils. 1) The contents of organic C (C), hydrolyzable carbohydrate (HC), readily hydrolyzable hexose (RH), and dithionite-citrate-bicarbonate soluble Al and Fe in the bulk soils and the aggregate size fractions were much higher in group A than in group B. 2) Among the macroaggregate size fractions of group A, the contents of the organic components such as C, HC, and RH generally increased with increasing aggregate size. The Al tended to be concentrated in the 0.25 to 1.0 mm size fractions. On the other hand, in group B, the organic and inorgaic components showed decreasing tendency with increasing aggregate size. 3) In group A, larger amounts of C, HC, RH, Al, and Fe were distributed in the macroaggregate than in the microaggregate size fractions. No such trend was observed in group B. 4) The degree of macroaggregation was much higher in group A than in group B. In group A, the higher the RH and Al contents, the higher the degree of macroaggregation. No such relationship was observed in group B. 5) From the results obtained, it was suggested that active Al and microbial polysaccharides merit close attention as the factors in the macroaggregation of group A, although the significant factors in group B remained unclear.

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The pumice layer was derived from the northwest fringe of Taal Volcano somma in Kaybagal, Tagaytay City in the Philippines. It has a gravel diameter of 3 to 5 centimeters (cm). The pumice gravel has a yellow surface color and a black inner color. These were observed using an optical microscope and scanning electron microscope (SEM). The chemical and mineralogical constituents were determined using a electron probe micro analyzer (EPMA), and X-ray diffraction apparatus. The results obtained from the optical microscope and SEM showed bubbles in the black or inner part of the pumice, while the surface showed weathered fine particles. Some of the bubbles observed were also partly weathered. The X-ray diffraction pattern showed smectite as the predominant mineral in the yellow surface layer, while amorphous materials were predominate in the black inner part. We speculate that smectite of the pumice may result from the weathering of amorphous glass in the inner part of pumice.

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農耕地土壌の分類第二次案改訂版から農耕地土壌分類第三次改訂版への読替え試行を行い,問題点を検討した。読替えは,既存の断面調査票と土壌分析値を用い,北海道と富山県で行った。このような方法によって大部分の土壌の読替えは可能であるが,読替え試行においていくつかの問題が明らかになった。実際の読替え作業における問題は,調査票への記載不足,判定基準の違い,および土壌分析値の不完全さなどである。これには既存の情報をできるだけ収集し,推定と予測を加えて総合的に判定することでかなり対応ができる。また,既存の土壌図は古いため,主に圃場整備に伴って土壌が変化し,現状と異なっている。このような地点は場所の特定も比較的容易であり,簡易調査法によって補完することが必要である。次に,3次案そのものには以下のような問題が明らかになった。1)低地土や台地土から黒ボク土に,逆に黒ボク土から台地土や火山放出物未熟土になるといった,従来の分類との継承性の問題があった。これは,定量的基準と切り取り法を用いたことによる,分類基準の厳密化と客観的分類の結果であり,やむを得ないものである。2)泥炭土については,とくに客土を行った土壌について,表層無機質の定義が薄過ぎるのではないかという問題があった。3)低地土などで,斑紋の形態を重視しているが,一般化しているとはいいがたい。判定についてのマニュアル作成などにより定義の普遍化が必要である。4)低地土と台地土(または山地土)の定量的境界は定義されているが,山地・丘陵地と台地の定量的境界は未設定である。5)母材については定量的基準の設定と軽石流や火砕流堆積物などをどう扱うか検討しなければならない。6)次表層は,地表下20〜60cmの間の土層と定義されているが,複数の層からなる場合の判断は定義されていない。7)土壌コードや,土壌統群と土壌統の名称に矛盾が見られ,整合性を図る必要がある。以上のような問題に対応するためには,責任ある組織で改変をする必要があり,土壌命名委員会の設置が望まれる。

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