Biopolymeric compound from olive oil chain by-products used as enhanced controlled-release biofertilizer

The valorization of olive oil by-products into sustainable biofertilizers can help reduce environmental impacts associated with conventional agricultural practices. In this study, lignin, bioactive compounds, and nutrients were valorized from olive oil chain by-products, i.e., olive mill wastewater (OMWW) and olive pomace, for the production of a starch-based activated–biopolymeric compound (BPC-A) with enhanced controlled-release properties. The efficiency of BPC-A in terms of nutrient release was studied in a 90-day soil incubation column leaching experiment, and the results were compared to those observed for a traditional NPK fertilizer and OMWW. BPC-A showed a gradual nutrient release, particularly for soluble N (both NH₄⁺-N and NO₃⁻-N forms), with about 55 % of the applied N dose released over 90 days. In addition, cumulative analysis of water-extractable organic C and CO2 respiration revealed that although BPC-A increased the available content of C in the soil and thus in the leachates, it nevertheless resulted in the lowest cumulative emissions of CO2 (BPC-A < NPK < OMWW). Moreover, the microbial activity in the 90-day soils revealed that BPC-A stimulated the highest hydrolytic activity, suggesting no toxic effects on soil microorganisms. These results highlight the potential of BPC-A as a controlled-release biofertilizer that combines long-term nutrient release efficiency and valorization of agro-industrial residues.