沖縄本島における造成土壌の表土とその流出土の物理性

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The made lands brought about by Agricultural Development Programs are said to be one of causes of runoff soils owing to the soil erosion. It is an urgent need in Okinawa island to study the cause and process and the efflux of soils, and to prevent and remove runoff soils. The objective of this study was to investigate the physical properties of the surface soils and the runoff soils of the made land of Okinawa island. Samples of surface and runoff soils were collected from ten selected sites. The collected samples were known in Okinawa dialect as: "Kunigami Mahji" (red and yellow soil or the other stone soil, strong acidic); "Shimajiri Mahji" (dark red soil or Ryukyu-limestone soil, neutral to weakly acidic); and "Jahgaru" (grey upland soil or mudstone soil, alkaline). The results are summarized as follows: 1) The value of the clay, dispersion ratio and erosion ratio of all soil samples were higher than each of criteria for the erodibility; 2) A positive high correlation between dispersion ratio (Dr) and/or erosion ratio (Er) was observed the content of the soil particles (CSP) dispersed by distilled water alone. It seems possible to estimate the both ratios and judge the erodibility by using the regression equations which were as follows: Y= 103.25X+10.06 [where Y=Dr (1/20)% and X=CSP (kg/kg oven-dry soil) in the soil particles less than 0.05 mm, r=0.956*** (significant at 0.1% probability level)]; Y=102.10X-3.84 [Where Y=Er(1/20)(%) and X=CSP in the soil particles less than 0.05, r=0.891***]; Y=130.76X+1.20 [Where Y=Dr (1/50) (%) and X=CSP in the soil particles less than 0.02 mm, r=0.987***]; Y=105.01X+0.40 [Where Y=Er(1/50) (%) and X=CSP in the soil particles less than 0.02 mm, r=0.982***]; 3) The texture of surface soils was light clay in the both soils of "Kunigami Mahji" and "Shimajiri Mahji", and heavy clay in "Jahgaru". "Kunigami Mahji" had the highest gravel content. There was also a tendency for "Kunigami Mahji" to have high sand fraction in the surface soils of made land, and to have high clay and silt fractions in the runoff soils. "Kunigami Mahji" had the most distinctive soil color in water. It was expected that the amounts of runoff soil of "Kunigami Mahji" were smaller than those of the two others.
社団法人日本土壌肥料学会の論文
1994-04-05

沖縄本島における造成土壌の表土とその流出土の物理性

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