Abstract
In this report the natures of soil humus were studied colorimetrically by the use of electrophotometer.After the results the authors obtained the following conclusions. I)The humus of dark brown to black coloured volcanic ash soils has generally same characteristics in many places throughout japan, it has always a small colour-quotient (Farbquotient) and a large colourindex (Farbzahl).It is regarded, therefore, that this humus has been subjected to intenced humification and has become very stable and acumulative. Of Ando-soils (after U.S.A. idea) the above humus also may be detected. Of other upland soils, on the contrary, the humus has rather contrast nature and is unstable ; a colourquotient being large and a colour-index being small. 2)The humus of peat soil has a large colourquotient and a small colour-index and does not contain A-type of humic acid.With the diminution of the influence of ground water, the above humus makes it's colour-quotient more larger and it's colour-index more smaller, to the result that it becomes to contain humic acid of A-type and to obtain the nature of that of upland soils.
