Abstract

The amounts of phosphorus and potassium in the soils, available to the plant growth, were determined by the Aspergillus niger method after Niklas and were brought to be compared to the degrees of soil responses to phosphorus as well as potassium fertilization. With 38 soils from several localities the following conclusions were obtained : 1) Aspergillus niger method was not a suitable means to determine the amount of available potassium because of the fact that the growth of aspergillus micellium was influenced more by the amount of phosphorus than by that of potassium. 2) The amount of micellium was increased by adequate application of phosphorus. 3) The production of micellium by aspergillus in the soil was observed to be reversely related to the response of soil to phosphorus fertilization. 4) Aspergillus niger method was concluded to be one of the rapid laboratory tests for the determination of the amount of available phosphorus to the plant growth.