国頭マージ地域における流出赤土の粘土鉱物 2,3 の理化学性について(農芸化学科)
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概要
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真平原造成地の土壌は赤黄色を呈し, 粘板岩や国頭礫層を母材とする強酸性の国頭マージで, 約60%の分散係数(率)を示す受食性土壌の特徴を有した。土性は粘土含量37%のLiCを示し, CECは約7.5me/100gで置換性Mg量はCa量より約4倍多く, 塩基飽和度は約8%を示した。粘土鉱物組成は養分保持力の小さい鉱物が主で, Ktが主要鉱物をなし他にCh/It, Vt-Chが随伴し, Itも附随した。造成地近くを流れる久志オー川に沈積した流出赤土は, 土壌侵食の初期段階においていずれもpHはほとんど中性を示した。粒径組成は最上流地点以外では粗砂が85∿95%で, いずれもLSの土性を示し, 3カ月後には上流寄りの中間地点から同様の土性が見られた。CECはほとんど1me/100g前後を示し, 上流ほど造成地土壌のCECに近似した。流出赤土には置換性Caがかなり供給され, 塩基飽和度は50%以上に高まった。粘土鉱物組成はItやKtが主体で, Ch/Itが随伴し, 中間および最下流地点ではChも附随した。造成地土壌の粘土鉱物組成とは異なり, 流出赤土の粘土部分には混層鉱物が相対的に減少し, Vt-Chが消失する傾向が示唆された。Clay mineralogy and some of physical and chemical properties of the soil sediments eroding from the reclamation land into a nearby stream were investigated in order to accumulate data on the soil erosion situation and for future measures of soil protection. The soils of the reclamation land of Mahirabaru showed the properties ofKunigami maajisoils which were derived from slate and Kunigami gravels. And they were red to yellowish, strongly acidic and light clay in texture containing 30% clay. The dispersion coefficients of the soils were about 60% which fall in the category of easily erosive soil. The CEC and base saturation percentage were about 7.5 me/100g and 8%, respectively, and exchangeable magnesium contents were 4 to 5 times than calcium contents. Generally dominated were clay minerals small in base holding capacity. And the main crystalline minerals in the clay fraction were kaolin minerals accompanied by a moderate amounts of chlorite/illite mixed-layer mineral, vermiculite-chlorite intergrade mineral and a minor amount of illite. The reddish soil sediments that had been eroded from the Mahirabaru reclamation land into the Kushi - Okawa stream were almost neutral in reaction in the first period. Their texture in the beginning was mostly loamy sand containing 85 to 95 percent of coarse sand fraction except for the uppermost stream site near the reclamation land. The loamy sand textures were found only in the middle and down stream sites three month later. The CEC was about 1 me/100g in most samples, but the sample closest to the reclamation land showed a higher CEC. Base saturation percentage of the reddish sediments was higher than that of the reclamation land indication a supply of calcium from the stream water. In the clay fraction identified were kaolin minerals and illite in a large quantity accompanied by a small amount of chlorite/illite mixed-layer mineral. Chlorite were identified only in the middle and lower stream site. Relative decrease in mixed-layer minerals and disappearance of vermiculite-chlorite intergrade mineral in the reddish sediments suggested some changes of mineralogical compositions from that of the reclamation land.
- 琉球大学農学部の論文
- 1982-12-01
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