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No.25 (1978/12) >

Title :ジャーガルとその母材に関する研究 : (第 4 報)沖縄本島, 具志頭村具志頭および中城村新垣土壌(層)断面の粘土鉱物(農芸化学科)
Title alternative :Studies on theJaagarusoils and their parent materials : IV. Clay minerals of soil profiles at Gushikami, Gushikami-son and Arakaki, Nakagusuku-son Okinawa Island (Department of Agricultural Chemistry)
Authors :渡嘉敷, 義浩
名城, 敏
大屋, 一弘
西垣, 晋
Authors alternative :Tokashiki, Yoshihiro
Nashiro, Satoshi
Oya, Kazuhiro
Nishigaki, Susumu
Issue Date :1-Dec-1978
Abstract :沖縄本島南部の具志頭村具志頭(O-12)および中部の中城村新垣(O-13)のいずれも典型的な"ジャーガル"土壌(層)断面から, "ジャーガル"およびその母材の泥灰岩をそれぞれ採取した。そして, 土壌の物理性および化学性に重要な影響を及ぼすと考えられる非結晶質成分の特徴を調べるために, 両断面の"ジャーガル"および泥灰岩の粘土部分にジチオナイト(ハイドロサルファイトナトリウムー炭酸水素ナトリウムークエン酸ナトリウム)処理, その処理後に0.15Mシュウ酸ナトリウムあるいは0.5N水酸化ナトリウム処理による選択溶解-示差赤外吸収スペクトル法の半定量鉱物分析法を適用した。また2,3の理化学性, 粘土部分の結晶質成分およびシルト部分の1次鉱物組成も調べた。ジチオナイト可溶成分は両断面では約6∿8%で, 上層ほど幾らか多い傾向を示した。そして具志頭の断面で64%前後, 新垣で77%前後をそれぞれ酸化鉄が占めた。ジチオナイト可溶成分はいずれも未同定成分の特徴を示し, そのSiO_2/Al_2O_3比はいずれも3以上で著しく大きく"ジャーガル"より泥灰岩層で2倍以上高かった。シュウ酸ナトリウム可溶成分は断面の相対応する層間にほぼ同量存在し, 他の2つの可溶成分より量的に多く最上層の"ジャーガル"に下の泥灰岩層より約2倍量多かった。そして具志頭の断面で35%前後, 新垣で39%前後をそれぞれ酸化鉄が占めた。シュウ酸ナトリウム可溶成分は, SiO_2/Al_2O_3比が"ジャーガル"および泥灰岩層のいずれも3以上で後者に幾分増える傾向を示し, いずれも未同定成分の特徴を示した。
水酸化ナトリウム可溶成分は量的にはジチオナイト可溶成分量に近似し, シュウ酸ナトリウム可溶成分量より少ない。そして両断面ともに酸化鉄が含まれないのが特徴である。水酸化ナトリウム可溶成分は両断面のいずれも未同定成分の特徴を示し, そのSiO_2/Al_2O_3比が下層ほど増加する傾向を示し, "ジャーガル"より泥灰岩層で数倍も著しく高かった。なお, 他の糸満市阿波根(O-1)の典型的な"ジャーガル"土壌(層)断面でも同様の特徴および傾向が認められ, これらの結果は"ジャーガル"と泥灰岩における非結晶質成分の特徴および一般的な傾向として見なした。一方, 両断面のpHは具志頭表土の弱酸性を除きいずれも弱アルカリ性, 土性は"ジャーガル"がいずれも埴壌土, 泥灰岩が壌土かシルト質埴壌土を示した。粘土部分の結晶質成分は両断面ともにほぼ80∿90%で, "ジャーガル"よりも泥灰岩層に幾らか多くなる傾向を示した。そして結晶質成分はモンモリロナイトおよびイライトが主体を占め, 他にバーミキュライトークロライト中間種, バーミキュライト, クロライトおよびカオリン鉱物が随伴した。またシルト部分の1次鉱物は両断面ともに石英が主体を占め, それにごく少量の長石が随伴し, これらの他にごく少量のクリストバライト, カルサイトおよびドロマイトが随伴するがそれらの存否は層間で異なった。
Two profiles of "Jaagaru" which generally by an Okinawan dialect implies soils derived mainly from marl deposit were selected at Gushikami (No. O-12) in the southern part of Okinawa Island and at Arakaki (No. O-13) in the central part of the same island in order to characterize the amorphous constituents in the clay fraction that carries important relations to soil genesis, and physical and chemical properties of the soil. Samples were collected from 3 different depths of the respective profiles; namely 0-20,20-100 and 100-270cm at Gushikami and 0-20,20-70 and 70-210cm at Arakaki. Amorphous constituents in the clay fraction were studied by means of selective dissolution, which included dithionite (Na_2S_2O_4-NaHCO_3-Na-citrate) treatment and successive dissolution with 0.15M Na-oxalate or 0.5N NaOH treatment, and by use of differential infrared spectroscopy. In addition to amorphous constituents, crystalline minerals in the clay fraction and primary minerals in the silt fraction were also examined by means of X-ray diffraction as well as color and particle-size distribution of the samples. The dithionite soluble materials comprised 6 to 8% of the clay fraction with somewhat decreasing tendency by the depth at the both profiles. Iron oxides in the dithionite soluble fraction were about 64% and 77% in Gushikami and Arakaki profile samples, respectively. Amorphous materials dissolved by dithionite were characteristic of the "unidentified" material carrying the SiO_2/Al_2O_3 molar ratio greater than 3 in every samples. The SiO_2/Al_2O_3 molar ratio of the deeper layer consisting of marly mudstone was 2 times greater than that of the top layer. The Na-oxalate soluble materials were the most quantitative among the three soluble materials, namely dithionite soluble, Na-oxalate soluble and NaOH soluble. The quantity of Na-oxalate soluble material was about 2 times greater in the top layer than in the deeper layers; the quantity in the layers of the one profile was very similar to the other profile. Iron oxides in the Na-oxalate soluble fraction were about 35% for Gushikami profile and about 39% for Arakaki.
All of the Na-oxalate soluble materials showed characteristics of "unidentified" as examined with the differential infrared spectroscopy. The SiO_2/Al_2O_3 molar ratio was greater than 3 and it somewhat tended to increase by the depth of layers. The quantity of NaOH soluble materials was about equal to that of the dithionite soluble. No iron oxide was found in the NaOH soluble fraction. The examination by differential infrared spectroscopy indicated that this fraction was also characteristics of "unidentified". The SiO_2/Al_2O_3 molar ratio of the fraction increased by the depth of layers. The authors assumed that the overall tendencies about the quantity and vertical distribution of soluble amorphous fractions were very common for "Jaagaru" profiles because Ahagon profile (No. O-1) reported in a previous paper very much resembled the characteristics described above. The contents of crystalline materials in the clay fraction ranged from 80 to 90%, and somewhat tended to increase by the depth at both of Gushikami and Arakaki profiles. The dominant crystalline minerals identified were montmorillonite and illite, which were accompanied by a small quantity of vermiculite-chrolite intergrade, vermiculite, chrolite and kaolin minerals. The primary minerals in the silt fraction consisted mostly of quartz and less of feldspar through the respective profiles. Cristobalite, calcite and dolomite were also identified as minor crystalline constituents varying in presence by layers. Reactions of the samples were all slightly alkaline except for the surface layer of Gushikami which showed slightly acid reaction. The texture was clay loam for the surface layers and was loam to silty clay loam for the deeper layers.
Type Local :紀要論文
ISSN :0370-4246
Publisher :琉球大学農学部
URI :http://hdl.handle.net/20.500.12000/4193
Citation :琉球大学農学部学術報告 = The Science Bulletin of the Faculty of Agriculture. University of the Ryukyus no.25 p.159 -170
Appears in Collections:No.25 (1978/12)

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