Microbial solubilization of rock phosphate on media containing agro-industrial wastes and effect of the resulting products on plant growth and P uptake

Four agro-industrial wastes were assayed as substrates for microbial solubilization of rock phosphate ( RP). Sugar beet wastes (SB), olive cake (OC) and olive mill wastewaters ( OMWW) were treated by Aspergillus niger, and dry olive cake ( DOC) was treated by Phanerochaete chrysosporium. In conditions of solid- state fermentation 46% of SB and 21% of OC were mineralized by A. niger while 16% of DOC was mineralized by P. chrysosporium. Repeated- batch mode of fermentation was employed for treatment of OMWW by immobilized A. niger, which resulted in conversion of 80% of the fermentable sugars. Acidi. cation of all media treated by A. niger was registered with a simultaneous solubilization of 59.7% ( SB), 42.6% ( OC), and 36.4% ( OMWW) of the total P present in the RP. The same mechanism of RP solubilization was observed in DOC- based medium inoculated with P. chrysosporium but other mechanisms were probably involved during the process. A series of microcosm experiments were then performed in the greenhouse to evaluate the e. ectiveness of the resulting fermented products. All amendments improved plant growth and P acquisition, which were further enhanced by mycorrhizal inoculation. The level of all studied parameters including the root mycorrhizal colonization depended on the substrate characteristics. The reported biotechnological schemes over a potential application particularly for degraded soils.