Abstract
Influences of extracting temperature on the quality and quantity of diluted sodium hydroxied soluble humus were studied by comparing the humus extracted at room temperature (303 K) and under heating on the boiling water bath (373 K), using 127 samples consist mainly of volcanic ash soils in Japan. Extraction at room temperature decreased the amount of humus extracts by 5〜50% compared with the heating extraction, while it increased the darkness of the humus extracts, measured by the absorbance at 600 nm per extracted carbon (CD/C: Color Density per extracted carbon). Its darkness was somewhat strengthened by heating after the extraction. Most of the decreased amount of humus extract at room temperature was recovered by the secondary extraction by heating of the residue of the room temperature extraction. Therefore, "the heating extract" was considered to be composed of the primaty extract at toom temperature and the secondary heating extract from the residue of the primary extraction. The latter humus fraction was considered to be extractable only with heating and lighter in color than the former. The secondary extract was contained abundantly (about 50% of "the heating extract") in the soils with weakly humified humus, while less in Ando solis with highly humified humus. This fraction greatly affected the properties of "the heating extract". Thus, the comparative differences between the optical properties of humus extracted at room temperature and under heating were not caused only by the alteration of the humus with heating but also by the extraction of the humus with different characteristics.
