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. Acidification 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 effectiveness 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 offer a potential application particularly for degraded soils.