Patè olive cake and its solid extract as amendments for ryegrass (Lolium perenne L.). Effects on soil chemical, microbiological and enzymatic characteristics and on plant yield and N content

A peculiar solid olive mill waste called Patè Olive Cake (POC), produced by decanters of latest generation, and its derivative solid extract from centrifugation called ‘pellet’ were evaluated as soil amendments on a pot cultivation of ryegrass in subacid and sub-alkaline soils. Characterization of POC and pellet was performed to determine their main chemical characteristics and phytochemical profile by conventional methods, NMR and HPLC to evaluate their suitability for agronomic applications. In both soils, POC and pellet were applied and contrasted to (i) half dose of POC and pellet added of mineral nitrogen (N) and phosphorous (P) to correct the C:N ratio and to balance the phyto-nutritive formula, (ii) commercial mineral and organo-mineral fertilizers and (iii) untreated soil (Control). During the ryegrass annual cycle, the vegetative responses and the N concentration were monitored in the epigeal biomass. At the end of the experiment, soil samples were taken from the pots to determine the main physicochemical characteristics and to carry out genomic and enzymatic investigations. Both soils treated with POC and pellet supplemented with N and P showed a significant increase in biomass productions compared to Control (+36.32%) and to commercial fertilizers (+14.34% and+16.41%, respectively, to mineral and organo-mineral fertilizers). In all treatments, higher cumulative biomass productions were observed in the subacid soil (+7.02%). In both soils, abundance and structure of fungi and bacteria communities showed no difference compared with the Control. Furthermore, enzymatic analysis indicated that microbial activity was not adversely affected by POC and pellet treatments. Our results indicate that POC and pellet can be used as soil amendments, contributing to reduce the use of chemical fertilizers and implementing circular economy and sustainability.