There are many erodibility indexes, but their deciding procedures are not so simple and they only indicate the soil natures statically. Then I think that the exponent “a” of the infiltration equation, I=bta derived by Mr. Musgrave could be a good erodibility index and made an experiment on it. Results of the experiment at the field are summarized as follows.
(1) This exponent is constant at any time for the same point and the value of “a” is admitted to reflect the dispersibility and infiltration capacity etc. of soil which are related to soil erosion.
(2) As this “a” is baued on soil structure, it is facilitate to distinguish between erodibilities of bare- and forest-land in neighbourhood.
(3) This measuring procedure can be carried out even on the site with forest litter and moreover when we use the turbid water to decide “a”, the difference in erodibility depending to have litter or not in the same forest land is easily distinguished.
(4) By comparison the data acquired by using pure and turbidwater, I found the erosion cantrol function of forest litter owing to filtration.
(5) This index can not yet presume the soil loss by erosion as the other indexes don't, but it will become to be able to presume after seasoning this index with factors such as gradient.
