Phosphate Solubilizing Bacteria and Fungi Isolated from Rubber (Hevea brasiliensis) Root Rhizosphere, Their Biofilm Formation and Phosphate Solubilizing Abilities

The ability of some soil microorganisms and their biofilm combinations to convert insolubleforms of phosphorus to an accessible form is an important trait associated with plant Pnutrition. The phosphorus solubilizing potential of bacteria and fungi isolated from Hevearhizosphere and their effective biofilm communities were evaluated using solid and liquidmedia under in vitro conditions. Phosphate solubilization ability of them were tested oncalcium phosphate media by analysing the soluble P content after incubation at 28±2°C. Outof the microbial isolates, 10 bacterial colonies and one fungal colony formed haloes (clearzones) around the isolate growing on solid media containing calcium phosphate as the solephosphate source. Spectrophotometric quantification of phosphorus solubilization in theliquid media showed that the ten bacterial isolates, and ten fungal isolates solubilizedinsoluble calcium phosphate in to the liquid media in the range of 200 – 450 and 200 – 300mg P L-1 respectively. Biofilm showed significantly higher P solubilization (853.3±25.17 mgP L-1) than their bacteria and fungi counterparts alone. Phosphate solubilization of bacteria,fungi and their biofilm could be attributed to the secretion of organic acids. A significant dropin the pH of the broth media (4.7 to 5.6) compared to the pH of the control treatment (6.8-7.0)was observed. pH change in the media could be due to secretion of organic acids bymicroorganisms and/or utilisation of compounds in the broth media. Although there was asignificant synergistic effect on P solubilization due to biofilm formation, pH in the liquidmedia of their mono cultures and biofilm were not significantly different. This observationwarrants further investigation

Exploring the Response of Paddy for Varying Levels of Soil Phosphorus in Tropical Soilscapes

Better management of soil Phosphorus (P) in crop cultivation leads to environmental and economic benefits. Proper understanding of the crop response to inherent soil P is important to develop site-specific recommendations. The objective of this study was to assess the yield response of paddy for varying levels of inherent available soil P in Alfisols and Ultisols. Surface soil (0-15 cm depth) P content was measured in 71 paddy fields in three districts of Sri Lanka, namely Anuradapura, Kurunegala and Polonnaruwa. Experiment plots (3x6 m) at each site comprised of ample application of N, P and K and an omission treatment plot of P. Total yield of each plot was recorded at the end of the season. The available P showed a large variability (range=from 2.7 ppm to 34.2 ppm, CV=78%) meanwhile 31% of the experimental sites were below the optimum soil P level for paddy (5 ppm).Omission plot treatments did not show a clear yield response for added P. Very low correlation coefficient between the yield of the omission treatment with the inherent P level (0.05), indicated that inherent P level will not determine the yield. The yield response was plotted against the Olsen P, and very low R2 value (0.03) indicated the Olsen P content does not clearly reflect the actual P requirement in every experimental sites. Short term availability of P from soil reserves cause to mask the effects of spatial variability on yield response and it was concluded that further studies are required to assess P dynamics to take SSNM decisions.Keywords: Paddy, Phosphorus, Site specific nutrient managemen