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Availability of Phosphorus as Influenced by Soil Microorganisms

A. ALI
Department of Microbiology, University of Dhaka, Dhaka 1000, Bangladesh

M. A. Z. MOLLA
Department of Microbiology, University of Dhaka, Dhaka 1000, Bangladesh

S. I. KHAN
Department of Microbiology, University of Dhaka, Dhaka 1000, Bangladesh

M.A.Islam
Department of Soil Science, University of Dhaka, Dhaka 1000, Bangladesh

Abstract/ Executive Summary:

Phosphate availability potential of microorganisms encountered in the non-rhizosphere and rhizosphere soils of ryegrass and rice was evaluated. Mixed cultures, Bacillus, Pseudomonas, Agrobacterium and Penicillium species were superior to the Aspergillus, Proteus, Serratia and Micrococcas species. The mixed cultures were found to be most effective while the Micrococcus sp, was least effective. Availability of phosphate was more in non-sterile than sterile soils. The viable counts of Streptomyces, Aspergillus and Penicillium species were relatively higher than that of bacterial species and mixed cultures. There was a decrease in the soil pH, However, there was no relationship between the amount of available phosphate and the decrease in pH.

Keywords: Availability of phosphorus, Soil microorganisms, Rizosphere, Ryegrass, Rice

Location: Dhaka University

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity: Fertilizer

Objectives:

To isolate and identify phosphate dissolving microorganisms from non-rhizosphere and rhizosphere soils of ryegrass and rice grown in the farmers' field.

Methodology:

Soil samples from the non-rhizosphere and rhizosphere soils of ryegrass (Secale cerele) and rice (Oryza sativum) grown in the farmers' field were taken for isolating phosphate dissolving microorganisms following Sperber’s method . The phosphate dissolving microorganisms were grown on Bunt and Rovira medium with tricalcium phosphate. Colonies of phosphate dissolving microorganisms were detected by the formation of clear zones around them when incubation was continued tor 15 days at 25⁰C. The isolates of bacteria and actinomycetes were identified according to the Bergey's manual of determinative bacteriology (10) and fungal cultures after "A Manual of Soil Fungi".In this experiment, 300g Chakla soil mixed with compost at a rate of 1g/100g soil was placd n 500ml Elenmeyer flasks. In a total of 66 flasks, half of them were autoclaved for three consecutive days at l5 p.s.i. (121⁰C) for one hour daily. The other half was left unsterilized. The pure cultures of bacteria (species of Bacillus, Pseudomonas, Micrococcus, Proteus, Serratia and Agrobacterium), fungi (species of Aspergillus and Penicillium) and actinomycetes (Streptomyces sp.) were grown on nutrient agar, potato dextrose agar and Czapek-Dox agar respectively. Freshly grown cultures of respective microorganisms were suspended in sterile water 25 ml of suspension of each culture having a concentration of approximately 5.6×106 cells/ml of bacteria, actinomycetes and spore suspensions of fungi were inoculated into sterile and non-sterile soil-containing flasks. The cultures with the soil samples were mixed thoroughly. Control flasks for sterile and non-sterile soils were not inoculated. Moisture was maintained at 50% of the maximum water holding capacity. The flasks were incubated at 30⁰C (±l) for 91 days. Microbial counts were determined by standard dilution plate method using Bunt and Rovira's agar medium at regular interval of 7 days from the date of incubation. The available phosphate (N/500 H₂SO₄ at pH3 extractable) was determined colorimetrically by chlorostannous blue color method as outlined by Jackson at regular interval of 7 days from the date of incubation. At similar intervals the changes in pH, was also recorded using a Corning pH meter .

Source of Information: Journal of Bangladesh Academy of Sciences,Vol. 14, No.1, 115-125, 1990

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The mixed cultures were found to be most effective while the Micrococcus sp, was least effective. Availability of phosphate was more in non-sterile than sterile soils. The viable counts of Streptomyces, Aspergillus and Penicillium species were relatively higher than that of bacterial species and mixed cultures. There was a decrease in the soil pH, However, there was no relationship between the amount of available phosphate and the decrease in pH.

Knowledge Management: Journal