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The Science Bulletin of the Faculty of Agriculture. University of the Ryukyus >
No.23 (1976/12) >

 
Title :ジヤーガルとその母材に関する研究 : (第 2 報)沖縄本島, 糸満市阿波根および西原村棚原土壌断面における粘土鉱物と水溶性成分について(農芸化学科)
Title alternative :Studies on theJaagarusoils and their parent materials : II. Clay minerals and water-soluble constituents of twoJaagarusoil profiles on Okinawa Island (Department of Agricultural Chemistry)
Authors :大屋, 一弘
渡嘉敷, 義浩
高江洲, 均
多喜, 和彦
西垣, 晋
Authors alternative :Oya, Kazuhiro
Tokashiki, Yoshihiro
Takaesu, Hitoshi
Taki, Kazuhiko
Nishigaki, Susumu
Issue Date :1-Dec-1976
Abstract :沖縄本島南部, 糸満市阿波根および西原村棚原に堆積する典型的な2つの"ジヤーガル"土壌断面を選定し, 各断面をおのおの5層に分け, 土壌断面中の理化学性, 粘土鉱物組成, および水溶性成分の移動・集積について調べた。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, 水溶性成分は蒸留水の浸出で溶出する成分中Siを比色法, Fe, Ca, Mgを原子吸光法, Na, Kを炎光法を用いておのおの測定した。典型的な"ジヤーガル"とその母材の土壌反応はいずれも弱アルカリ性反応を呈し, 粒径分布はシルト部分や細砂部分の含量が高く, 土性はSiCLあるいはLを示した。また, 有機炭素は1%以下で, CEC25∿34me/100gを示し, 置換性塩基中Caは31∿39me/100gで最も多量に含まれた。Kは1∿3me/100gで最上層と最下層に多く含まれ, Mgは1∿4me/100g, Naは1∿2me/100gでいずれも上層から下層へ漸次増加した。粘土部分の非晶質成分はジチオナイト可溶成分が4∿ 11%, そのうちFe_2O_3が2∿4%含まれ, 0.15Mシュウ酸ナトリウム可溶成分が8∿22%含まれた。後者の成分は上層から下層へ量的に漸次減少し, いずれもSiO_2/Al_2O_3分子比が2に近い値を示した。また, 粘土部分の結晶質成分は71∿85%含まれ, 上層から下層へ幾分増加した。断面中の鉱物組成は, 全層にモンモリロナイトが主体を占め他にイライト, Al-バーミキュライト, クロライト, カオリナイトがいずれも少量随伴した。一方, シルト部分は著しく多量の石英とごく少量の長石とが全層に含まれ, 両鉱物の他にごく少量のカルサイト, ドロマイト, クリストバライトが付随し, これらの鉱物の存否は各層間で異なった。"ジヤーガル"土壌断面での水溶性成分中Si, Feの溶出量および溶出の型は土壌断面の各層間で異なった。これに対しCa, Mg, K, Naの塩基類は溶出量および溶出の型に土壌断面の各層間でほぼ一定の傾向がみられた。Caは数10PP^m溶出し, 5mの深さの泥灰岩層に著しく多かった。Mg, Naの溶出量は1∿3ppmで上層から下層へ漸次増加し, 特にMgは最下層の泥灰岩層では5ppmに達した。Kは2∿4ppm溶出し最上層と最下層の泥灰岩に多く, 中間層ではMgとNaの溶出量の間にあった。なお, 連続的に抽出測定される水溶性塩基のMg, K, Naは或る比率をもって置換性部分から放出されるものと思われる。また, Caの大部分は遊離のCaCO_3として存在することが示唆された。
Soils derived from the marl of Shimagiri debs distribute in the central and southern parts of Okinawa Island and are called "Jaagaru" by an Okinawan dialect. The authers as reported in the previous paper initiated to study physical, chemical and mineralogical properties of "Jaagaru" soils in relation to their genesis on the Shimajiri beds. The present study was to investigate physical and chemical properties, clay mineralogy, and movement and accumulation of water-soluble constituents in two typical "Jaagaru" soil profiles. The profiles were selected at Ahagon, Itoman city and Tanahara, Nishihara village in the southern part of Okinawa Island, and five horizons were distinguished in the respective profiles. Determination of pH, exchangeable base, CEC, particle size distribution, and organic carbon were studied as employed in the previous paper. Clay mineralogy was studied by means of selective dissolution and X-ray diffraction. Water-soluble constituents such as Si, Fe, Ca, Mg, K and Na were extracted with distilled water from the samples of respective horizons; Si was determined collorimetrically, Fe, Ca and Mg were with atomic absorption, and K and Na with a flame photometer, respectively. The "Jaagaru" soils and their parent materials studied were weak alkaline, high in silt and fine sand fractions, and SiCL to L in texture. Organic carbon was less than 1% and CEC ranged 25 to 34me/100g through the profiles. About exchangeable base, the most abundant was Ca with the range of 31 to 39me/100g. Exchangeable K ranged from 1 to 3me/100g through the profiles but the top and the fifth horizon contained more K than the others. Exchangeable Mg and Na gradually increased from the top to the lower horizons in the range of 1 to 4me/100g, respectively. It was found that amorphous materials in the clay fractions consisted of 4 to 11% of dithionite soluble material and 8 to 22% of sodium oxalate soluble material. The former contained 2 to 4% of Fe_2O_3 and the latter decreased gradually from the top to the lower horizons with the molar ratio of SiO_2/Al_2O_3 being sustained close to 2. Crystalline materials were 71 to 85% in the clay fractions decreasing somewhat from the top to the lower horizons. The main crystalline mineral identified in the clay fractions was montmorillonite accompanied by a small quantity of illite, Al-interlayering vermiculite, chrolite and kaolinite. In silt fractions found were a large quantity of quartz and a small quantity of feldspar through the profiles. Calcite, dolomite and cristobalite were minor ones identified varying in presence by horizons. A generalizable tendency was not found in water-soluble Si and Fe among the horizons. Water-soluble Ca, Mg, K and Na, on the other hand, showed somewhat clear tendency through the profiles. Ca dissolved in water as much as scores of ppm through the profiles with the highest content in the lowest horizons. Water-soluble Mg and Na increased gradually from the top to the lowest horizons reaching from 1 to 5ppm in case of Mg and from 1 to 3ppm in case of Na. Water-soluble K ranged from 2 to 4ppm but more K was found in the top and the lowest horizons than in the others where its contents were intermediate between Mg and Na. From the obtained results that the quantity of exchangeable Ca exceeded CEC and that showed a large quantity of water-soluble Ca, suggested was that Ca in the studied profiles existed in a form of free carbonates to some extent. Also suggested was the equilibrium relationship between exchangeable and water-soluble base for future study, because correlations between the two forms of base was very high and water-soluble base was possible to be extracted successively.
Type Local :紀要論文
ISSN :0370-4246
Publisher :琉球大学農学部
URI :http://hdl.handle.net/20.500.12000/4296
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.23 p.165 -176
Appears in Collections:No.23 (1976/12)

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