Zinc Status of Some Illinois Soils as Estimated by an Aspergillus Niger Method
1953
An extremely sensitive semiquantitative method for bio-assay of zinc in soils with Aspergillus niger is described. Data at present do not permit the validation of the assay as an index of response by higher plants on soils of Illinois. Present investigations are being conducted to locate soils that will respond to zinc fertilization. It is hoped that these studies will show a positive relationship between the bio-assay of zinc in the soil and crop response, and perhaps lead to a chemical method which will appropriately measure the available form of zinc in soils. The method as outlined was used for acid soils and is not applicable to alkaline or calcareous soils. Although the procedure is relatively simple, extreme care must he exercised in order to prevent contamination with zinc from reagents and equipment. Reagent grade chemicals were used and purification of water and sucrose was effected by an ion-exchange resin. An acid cleaning solution was the most effective method tried for removing traces of zinc from equipment. Sterilization of the soil to be assayed is not recommended. The growth response of Aspergillus niger was related to known increments of zinc in 50-ml nutrient solution in 500-ml Erlenmeyer flasks. This relationship was used to evaluate the zinc status of soils. Florida soils known to respond to zinc fertilization ranged from 0.6 to 2.88 ppm zinc and Illinois soils ranged from 1.6 to 21.5 ppm zinc, according to the bio-assay. It is conceivable that a few Illinois soils may respond to zinc fertilization or are at least approaching a critical level.
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