On Evaporation at the Surface of Kuroboku Soil adjoining Akahoya or Bora Soil in Lower Layer

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Other Title
  • 下層にアカホヤまたはボラが存在するクロボク土壌面からの蒸発について
  • カソウ ニ アカホヤ マタハ ボラ ガ ソンザイスル クロボク ドジョウメン
  • Soil properties and water movement in the volcaaic deposit (Shirasu) area (V)
  • シラス地帯における土の特性と水の動態 (V)

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Evaporation Y (mm/day) from Kuroboku soils where the second layer was Akahoya soil or Bora soil was measured using a soil tank (ground-water recharge type), and evaporation from the water surface was measured using an evaporation tank (large type).<BR>Net radiation, X (ly/day), was measured at the same time. The relation between Y and X were obtained as follows:<BR>In a period from the first 10 days of August until the same period of October, <BR>Y=0.0114X+1.39: where soil layers were Kuroboku-Akahoya<BR>(r=0.815)<BR>Y=0.00812X-0.139: where soil layers were Kuroboku-Bora-Kuroniga<BR>(r=0.776)<BR>Y=0.0133X+0.0394: at the evaporation tank<BR>(r=0.844)<BR>Howewer, correlation was not very good from about the 10th of October until the latter part of November, due to air movement and temperature ranges (see Figs. 2-4).<BR>The influence of the Bora soil layer on evaporation judged from the evaporation ratio was a reduction of evaporation to about 0.5-0.6 (see Table 1).<BR>Changes of soil temperature with time showed a similar tendency. But, when the second layer was Bora soil, it was 1-2°C higher than when it was not Bora soil, and the time-lag at the highest temperature in each depth of soil was smaller than when the second layer was Akahoya soil (see Fig. 5).<BR>Changes of total potential with time were larger when the second layer was Bora soil. However, there were small changes every 50cm down (see Fig. 6).<BR>Values obtained by the foregoing method, using a soil tank (ground-water recharge type), on Kuroboku soil with a second layer of Akahoya soil were close to the values obtained when the heat balance method or PEBYT's method was used. But, they were larger when this method was used on Kuroboku soil with a second layer of Bora soil as shown in Table 2.

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