Levels of available micro-nutrient metals in some Japanese soils as measured byaspergillus nigerwith special reference to their threshold values

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Abstract
This paper presents the levels of available amounts of zinc, copper, and molybdenum as measured by Asp. niger (Mulder strain) in soils of Japan with special regard to their threshold values. Results obtained are as follow: 1) Levels of available zinc in soils examined ranged from 0.4 to 27 ppm. The threshold value for available zinc is adequelty represented as a function of the soil pH value, and was estimated to be around “0.5 × (soil pH value)-0.5” ppm (soil pH value >1). 2) Levels of available copper in soils examined ranged from 0.3 to 5 ppm, and the threshold value for available copper lies near 0.5 ppm. However, the value is more suitably represented as a function of the soil carbon content. This value was shown to be around “0.1 × (carbon % in the soil)” ppm. 3) Levels of available molybdenum in soils examined ranged from 0.01 to 0.13 ppm with the average about 0.10 ppm. The threshold value for available molybdenum is well expressed as a function of the soil pH. The value was estimated to be around “-0.04 × (soil pH value)+0.30” ppm (soil pH value <7.5).