PHOSPHORUS ASSIMILATION BY SOIL MICROÖRGANISMS

Abstract

Aspergillus luchueyi-sis decreased the pH of liquid culture media considerably in 11-14 days but the reaction became less acid as the incubation period was increased. A. minutus increased the pH in dextrose solution cultures after 2 wks.; it did not produce as much mycelium as A. luchuensis but contained a larger % of P and assimilated more phosphate. If the assimilation of P is accompanied by an increase in the pH of culture medium, A. minutus may have produced more acidity than A. luchuensis, the acidity being neutralized earlier in the incubation period. The P assimilation by .4. luchuensis was small in dextrin and sucrose solution cultures. Azotobacter chroococcum assimilated more P for the first 45 days than was made available, but for the 2nd period of 45 days more P was made available than was utilized. Addition of insoluble phosphate increased the amount of P assimilated during the first 45 days of the experiment and also increased the amount of water-soluble P during the 2nd 45 days. The native soil flora of Carrington loam was more effective in dissolving tri-calcium phosphate than was A. chroococcum. Different spp. of soil microorganisms probably affect the water-soluble P differently for some spp. may have a greater dissolving action than assimilating power, whereas with others the reverse may be the case.