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No.24 (1977/12) >

Title :ジャーガルとその母材に関する研究 : (第 3 報)沖縄本島, 西原村千原土壌断面における理化学性と粘土鉱物について(農芸化学科)
Title alternative :Studies on theJaagarusoils and their parent materials III. Physical and chemical properties and clay minerals of soil profiles at Senbaru, Nishihara village, Okinawa Island (Department of Agricultural Chemistry)
Authors :渡嘉敷, 義浩
比嘉, 靖
大屋, 一弘
西垣, 晋
Authors alternative :Tokashiki, Yoshihiro
Higa, Yasushi
Oya, Kazuhiro
Nishigaki, Susumu
Issue Date :1-Dec-1977
Abstract :沖縄本島中部, 西原村千原の本学農学部附属農場の新敷地造成地で, 泥灰岩層の上部に中性∿弱アルカリ性と強酸性とを各々示す2つの赤褐色土壌が, 各々直接堆積する土壌断面を選定し, 前者は6層に分けた各層, 後者は表土だけについて理化学性および粘土鉱物組成を調べ, また, 土壌反応の異なる2つの赤褐色土壌の生成についても考察した。理化学性は常法で調べたが, 炭素量は湿式燃焼重量法で有機炭素と無機炭素に各々分けて測定し, また, 80%メタノールによる可溶性塩類, および80%メタノール中1規定塩化ストロンチウム溶液により遊離の炭酸塩の溶出を抑制しながら置換性塩基とCECを測定した。粘土鉱物組成は主として選択溶解法とX線回折分析法を用いて測定した。赤褐色土壌(1∿3層)の土壌反応はいずれも中性∿弱アルカリ性, 全炭素は1.7∿0.6%で上層ほど高く有機炭素が1.7%で主体を占め, 土性はいずれもHC(重埴土)を示した。可溶性塩類の総量は0.24me/100gでそれの半分量をCaが占め, 層間で差異がなかった。置換性塩基の総量は11∿18me/100gでその90%をCaが占め, CECは22∿17me/100g, 塩基飽和度は80∿66%でいずれも上層から下層へ減少した。粘土部分の非結晶質成分中, ジチオナイト可溶成分はいずれも19%でその半分量以上を酸化鉄が占め, 0.5規定水酸化ナトリウム可溶成分は11∿15%で上層と下層に多く層間で異なった。結晶質成分は66∿70%でいずれもバーミキュライトークロライト中間種, イライトおよびカオリン鉱物が主要粘土鉱物で, 他にバーミキュライトが随伴した。シルト部分の1次鉱物はほとんど石英で, 他にごく少量の長石が含まれた。他の赤褐色土壌(1'層)では, 前述の赤褐色土壌の特徴にかなり類似したが, 土壌反応が強酸性を呈し, 有機炭素が著しく少なく, 土性がLiC(軽埴土)を示し, 可溶性塩類のほとんどをNaが占め, 置換性塩基の総量が1me/100g, 塩基飽和度が7%で著しく小さいことなどが, 前述の赤褐色土壌の特徴とは異なった。
一方, 泥灰岩層(4∿6層)の土壌反応はいずれも中性∿弱アルカリ性, 全炭素は0.3∿1.3%で下層ほど高く無機炭素が0.9%で主体を占め, 土性はLiC(軽埴土)∿SL(砂質壌土)で下層ほど砂含量が高かった。可溶性塩類の総量は層間で異なり0.19∿ 0.39me/100gでNaが50%を占め, 残りの半分量をCaが占めた。置換性塩基は21∿25me/100gでいずれの層も総量の70∿80%をCaが占め, 次にMgが20%前後を占め下層で少なかった。CECは24∿28me/100g, 塩基飽和度は88∿91%で層間で異なった。粘土部分のジチオナイト可溶成分は7∿5%でその半分量の3%前後を酸化鉄が占め, 0.5規定水酸化ナトリウム可溶成分は5∿8%で, いずれの成分も下層ほど減少する傾向を示した。結晶質成分は85∿90%で, モンモリロナイトおよびイライトが主要粘土鉱物で, バーミキュライトークロライト中間種, バーミキュライトがこれに続き, 少量のカオリン鉱物も含まれ, 最下層にはクロライトも少量随伴した。シルト部分の1次鉱物はほとんどが石英で, 他にごく少量の長石, クリストバライト, カルサイトを随伴したが, 後者は最下層にだけ含まれた。なお, 赤褐色土壌はサンゴ石灰岩を母材とする残積性の風化生成物ではなく, 運積性非固結堆積岩を母材とし局部的に周辺の地層や泥灰岩, 石灰岩などの影響を強くうけて生成されたことを推察した。
Two soil profiles with a reddish brown soil layer underlain by the marl deposit were selected in the agricultural experiment station located at Senbaru, Nishihara village near central part of Okinawa Island, and physical and chemical properties, and clay mineralogy were investigated in relation to soil formation. Soil samples were taken from 6 depths (0-20,20-120,120-170,170-250,250-320 and 320-600cm) of the first profile and from 1 depth (0-30cm) of the second profile. Physical and chemical properties of the soils were determined by commonly used methods. Inorganic- and organiccarbons were determined separately by a wet combusion-gravimetry technique. Soluble salts were extracted with 80% methanol. Exchangeable bases and CEC were determined by using normal strontium chloride in 80% methanol so that free carbonate would not dissolve. Clay minerals were studied by a selective dissolution method and X-ray diffraction technique. The both profiles were characterized, by the determinations carried out in the present study, as being composed by at least two layers of different origin. Of the first three depths, reactions were neutral to slightly alkaline, total carbon ranged from 0.6 to 1.7% decreasing with the depth. Organic carbon was the main source of the total carbon at the first depth. Texture was categorized as a heavy clay for the soils of the three depths. The summing up of soluble salts such as Mg, Ca, Na and K was 0.24 to 0.25me/100g, more than half of which was occupied by Ca. The total of exchangeable bases such as Mg, Ca, Na and K ranged from 11 to 18 me/100g, of which 90% was exceeded by Ca. CEC and base saturation percentage ranged from 17 to 22 me/100g, and from 66 to 80,respectively, and the both decreased with the depth. Nineteen percent of the amorphous portion in the clay fraction was soluble to dithionite solution. Ferric oxide occupied more than half of the dithionite soluble portion. Eleven to 15% of the amorphous portion was soluble to 0.5 N NaOH solution.
The clay fraction consisted of 66 to 77% of crystalline material of which major clay minerals were vermiculite, vermiculite-chlorite intergrade, and kaolin minerals accompanied by a minor amount of illite. The primary mineral in the silt fraction was mainly consisted of quartz accompanied by a small amount of feldspars. Of the second three depths of the first profile, reaction was neutral to slightly alkaline. Total carbon ranged from 0.3 to 1.3% increasing with the depth, and inorganic carbon dominated at the 6th depth. Texture was categorized as a light clay for the 4th and 5th depths and as a sandy loam for the 6th depth. The total of soluble salts ranged from 0.19 to 0.39 me/100g, where Ca and Na were the dominant ones. Exchangeable bases were 21 to 25 me/100g in the total, of which 70 to 80% was occupied by Ca. CEC and base saturation percentage ranged from 24 to 28 me/100g and from 88 to 91,respectively. The dithionite soluble portion was 5 to 7% of the clay fraction, half of which was determined as ferric oxide. The sodium hydroxide (0.5 N) soluble portion was 5 to 8%. Those portions soluble to dithionite and sodium hydroxide tended to decrease with the depth. The clay fraction of the second three depths consisted of 85 to 90% of crystalline material, in which the major clay mineral was montmorillonite accompanied by a moderate amount of illite, vermiculite and kaolin minerals, and a lesser amount of vermiculite-chlorite intergrade. A small amount of chlorite was found in the 6th depth. The primary mineral of the silt fraction consisted mainly of quartz accompanied by a lesser amount of feldspars and cristobalite. Calcite was identified in the 6th depth. The reddish brown surface layer of the second profile was much lower in pH (strongly acid) and organic carbon contents than that of the first profile. Its texture was a light clay. Na was dominat in soluble salts. The total of exchangeable bases was 1.0 me/100g and CEC was 14 me/100g. Base saturatio
Type Local :紀要論文
ISSN :0370-4246
Publisher :琉球大学農学部
URI :http://hdl.handle.net/20.500.12000/4238
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.24 p.205 -215
Appears in Collections:No.24 (1977/12)

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