Abstract:
Phosphorus (P) is a macro nutrient, which mainly presents as fixed forms in soils. The fixation
limits the P availability for plant uptake. Conventionally, P fertilizers are applied excessively for
upland vegetables and paddy fields in dry zones in Sri Lanka though these crops do not give
expected yields with increased P applications due to high fixation. The excessive usage of P
fertilizers not only adversely affects the root rhizosphere but also accelerates the diminishing of
the natural rock phosphate deposits used as the major source for P fertilizer production. Microbial
application is one of the sustainable and ecofriendly strategies to improve P solubility and,
thereby, to facilitate efficient use of the limited P resources. The laboratory experiment was
conducted for qualitative comparison of the ERP solubilizing capacity by the randomly isolated
microorganisms (PSM) in soils at the horticulture farm, Gannoruwa. Microorganisms extracted
from the diluted soil series were introduced to Pikovskaya agar media (PKV) containing ERP less
than 125 μm particle size in petridishes. Halo zones were developed by the P solubilizing
microorganisms, and these microorganisms were identified as Aspergillus flavus (PSF1),
Aspergillus niger (PSF2), Penicillum sp. (PSF3), and Aspergillus terreus (PS4) by morphological
studies. These PSMs were single spot inoculated for creating pure culture using 20 ml of PKV
media with ERP as prepared previously. Measurements of P solubilizing index (PSI) [(PSI=Colony
diameter + Halo zone diameter) / Colony diameter] and P solubilizing efficiency (PSE)
[(PSE=Colony diameter/Halo zone diameter) × 100%)] were taken in three, six, nine, twelve and
fifteen days intervals. Four replicates were done for each treatment. The PSI and PSE values were
recorded with descending order as PSF1(4.33)>PSF2(2.75)>PSF4(2.56)>PSF3(2.056) and
PSF1(335.06%)>PSF4(172%)>PSF2 (157.39% )>PSF3(110%), respectively. According to the
scale introduced by Silva Filho and Vidor, the P solubilizing capacity is low, medium, and high
when the PSI is lower than two, in-between two and three, and higher than three, respectively.
Accordingly, the PSF1 shows high P solubilizing capacity and other fungi show medium P
solubilizing capacities. Therefore, the PSF1 with ERP is identified as a potential P-biofertilizer for
improving the plant availability P in agricultural soils.
