Effect of biocomposites and biofertilisers on soil quality as part of a new approach to the valorisation of agricultural and agri-food waste

Abstract

The world's population growth has led to the intensification of agriculture worldwide, which is accompanied by an increase in the use of chemical fertilisers and plastics, but also by huge food losses and waste. AGRIMAX is a European project funded by the European Union and whose goal is to valorise organic waste from the agro-food sector into different high value-added products such as packaging, food ingredients, biofertilisers, and films and pots, in a perspective of circular economy. The objective of this work was to assess the effects of films, pots and biofertilisers, developed in the project, on soil quality in order to validate and demonstrate the use of these products in agricultural applications. In order to meet this objective, laboratory incubation experiments were set up over a 12-week period to test the impact of five biocomposites and three composts on different soil biochemical parameters. Among the biocomposites tested, two consisted of natural fibres and fungal mycelium, while the other three were bioplastics formed by a polybutylene succinate matrix (PBS). Two of the composts were improved by the addition of plant growth promoting microorganisms (PGPMs) and the third was a reference compost. The biodegradation of the products was evaluated according to the evolution of carbon mineralisation and was monitored over the entire incubation period, as was the net release of mineral nitrogen. CaCl2 extractable phosphorus, soil microbial biomass (MBC), phospholipid fatty acids (PLFAs) and the enzymatic activities of dehydrogenase, beta-glucosidase and N-acetyl-beta-D-glucosaminidase were measured only after 12 weeks. The majority of the biocomposites showed a significant degradation after 12 weeks of incorporation into the soil and a net immobilisation of nitrogen. They also demonstrated their capacity to improve the soil microflora and its activities during biodegradation. The only major concern caused by biocomposites in this study was their impacts on nutrient availability, which could be problematic for microbial and plant growth if no external sources are supplied to the soil. Compost mineralisation was relatively low and not significantly different between the composts tested, demonstrating their potential to sequester carbon. In general, composts had little influence on all the parameters tested, probably related to the absence of vegetation and the short duration of the experiment. The results of this study suggest that the biocomposites and composts tested have the potential to maintain or promote soil microbial activities and thus maintain soil quality. These new material formulations are therefore promising for the development of a more sustainable agriculture where yesterday's wastes are tomorrow's resources.