The relationship between soil loss and rainfall energy on standard soil erosion Testing plots. (3) (Fundamental studies on farmland conservation in Okinawa XI.) (Department of Agricultural Engineering)

現地における土壌侵食枠試験は1雨毎の観測を積み重ねることにより精度を高めることができるが, 結果は多くの雨による流亡土の観測もいくつかあった。然しトータルとしての降雨エネルギーと流亡土量との関係は把握できた。結果を要約するとつぎのとおりである。1)傾斜別試験区では傾斜が高い程流亡土量は多く, 土壌別では粘性の高いものが流亡土量が少ない。2)植生区では植付後2年目からはかなり高い侵食抑制効果が期待できる。3)観測期間中の流亡土量を土の仮比重1.4として土層厚(cm)に換算すると8°区, 5°区, 3°区, でA土壌ではそれぞれ3.6,2.5,1.4でありB土壌では1.0,0.8,0.3である。また植生区, 裸地区では年平均それぞれ3.0,4.4となっている。4)種々の土壌, 地形条件のもとで降雨の単位エネルギー当りの流亡土量を流亡係数として表わし当該地域の侵食性の指標としたい。終りに本研究の一部は昭和54年度文部省自然災害科学特別研究(代表者細山田健三)の補助により行なわれたものであることを附記します。The purpose of this study is to determine the coefficient of soil erosion factors applicable to the northern parts of Okinawa which excell in Kunigami Maji soil. Two experimintal fields have been selected for a soil erosion research at Yaka, Kin-son. The one consists of three plots (bare soil) which are set at an incline of 8,5 and 3 degrees respectively. The other consists of two plots (vegitative and non-vegitative) which are set at an incline of 10 degrees. The period of observation is from June 1977 to November 1979 in the former field and from July 1977 to December 1979 in the latter one. The rainfall energy of the area was calculated by using the equation y=916+331log_i which was formulated by Wischmeier and Smith and also the soil loss from each plot was measured during the observation period. The results of this observation are as follows : 1. The steeper the field plots were the more soil loss was observed. 2. The effect of vegitative cover in case of pineapples was shown gradually after one year growth. 3. It is desirable to establish the index of erodibiliy in an area by measuring the soil loss coefficent which was calculated by soil loss caused by a unit of rainfall energy