SPURWAY氏法による土壌の燐酸吸収力の簡易定量

抄録

Of twenty five soils from arable areas of Kanagawa Pref, absorptive power for phosphoric acid was determined by means of SPURWAY'S method. 2.6 gm of soils, in test tube, were added with 13 cc of the phosphate solution, and settled for one hour occasionally shakened. After the settling, the content was filtered and one c, c of the filtrate was applied to the determination. The method is of modified SPURWAY'S method by the authors. The degree of the absorptive power was designated by the amount of P_2O_5 remained in the supernatant liquid ; the amount was shown by the number of colourimetric chart in the following inclination : 1>2>3>4. Of the number, it is understood that with an increase of numerals P_2O_5,in the supernatant liquid, increases its amount ; consequently, of the soils of this case, the absorptive power for phosphoric acid becomes stronger with the decrease of numerals. Of the phosphate solution (0.13 gm of Na_2HPO_4+12 aq in 100 cc) two kinds were prepared as follows : one of pH 5.0 and the other of pH 9.6. For the former acetic acid was added and for the latter NaOH. The absorptive power of the soils has been observed to fluctuate considerably depending upon the kind of the reaction of medium, acidic or alkaline. Of the volcanic ash soil the above fluctuation has been observed to be conspicuous ; namely, it absorbs P_2O_5 much more in acidic medium than in alkaline medium. This fluctuation is considered by the authors to be used as one of the means of detecting the volcanic ash soil from the ordinary soils from other origin, and this consideration induced the authors to make this experiment with the scope of fixing the simple and rapid method of detedting so called volcanic ash soils. The results of the determination were tabulated as in Table 2,and confirmed the following conceptions : 1) Volcanic ash soils have, in general, the tendency to have stronger absorptive power for phosphoric acid than the soils of other origins, especially in the case of their being treated in the acidic medium. Among the volcanic ash soils, the above tendency seemed to be strengthened toward the subsoils. 2) By applying the results of cited in 1), there may be fixied a method of detecting volcanic ash soil materials from the materials of other origins, when the materials have not much humus. 3) By the use of the procedure, reported here, the absorptive power of soils for phosphoric acid may be ascertained in about seven grades according to its strength.