Satisfactory purification of the basal medium is obtained by autoclaving with 15 g/l A1203 (chromatographic analysis material) for 20 min. at 10 lb. pressure. Although Asp. niger spore colour method have been used for copper assay, the technique are not convenient with zinc. Mycelial dry weight are used as the criterion of evaluation in this work, and visual comparison of degree of sporulation and mycelial growth with those of zinc standard series may be used as a rapid and simple method of measuring available zinc in soils. Samples of 0.01-0.50g are employed, depending on the zinc status of the soil tested, and for most soils 0.05-0.10 g samples are used. The results obtained by Asp. niger method compare fairly favorably with the chemical method and, like in copper assay, except in a few soils the bioassay generally gives about twice as high values as the available zinc contents determined by chemical method (Hibbard's method.)
1) 九大農学部構内の土壌より分離した Asp.niger を試験菌とし, 再結晶法及びクロマトグラフ用活性アルミナによる吸着法の併用により純化した培養液を用いて30℃で7日間培養した後, その菌体乾燥重量を Zn standard series のそれと比較する方法によつて土壌中の可給態亜鉛の Bioassay を行つた. 2) 此の場合, 分生芽胞着生度及び菌体の生育程度の肉眼的観察による方法も簡便的に用いられると思われる. 3) sample の使用量は通常の土壌では0.05~0.10g/25 cc medium 位が適当である. 4) Asp.niger による土壌中の可給態亜鉛の定量値は, 銅の場合と同様に, Hibbard法による化学的な可給態亜鉛定量の結果とかなり同一の傾向を示すが, 若干の例外を除きその絶体値は大約2倍前後の結果を示した.