The effect of Penicillium bilaii on wheat growth and phosphorus uptake as affected by soil pH, soil P and application of sewage sludge

Penicillium bilaii may enhance P availability to plants, since it has been shown to increase plant growth and P uptake. There is currently increasing interest in using microorganisms to promote P mobilisation from organic P sources. An investigation was conducted to determine the effects of P. bilaii on P uptake and growth of wheat in the presence and absence of sewage sludge. Two soils differing in P contents and pH were used, as it was hypothesised that these affect the efficiency of P mobilisation. A pot experiment, in which wheat was grown for 35 days in a moderately acidic soil of low P status and a calcareous soil of moderate P status, was conducted. A full factorial design was used with two non-sterilised soils, three amendments [control, sewage sludge and triple superphosphate (TSP)] and two P. bilaii treatments (with/without). Shoot and root length, biomass and nutrient contents were analysed in plant, whereas soil samples were analysed for water-extractable P and soil pH. The shoot length and root biomass of wheat were significantly higher when sewage sludge was applied in combination with P. bilaii seed inoculation, in the moderately acidic soil. In contrast, shoot length and biomass and root biomass were higher with P. bilaii compared to the control, but no synergistic effects of P. bilaii and the organic P source were observed in the calcareous soil. A systematic, but not significant increase in total P uptake was found for all treatments inoculated with P. bilaii and for both soils, with the control of the low fertility moderately acidic soil being a notable exception. Sewage sludge was seen to be an efficient P source, on par with TSP in the moderately acidic soil. In the calcareous soil, the P. bilaii treatments without added P fertilisers had the greatest effect, with both root and shoot biomass increasing significantly.