Validation of bio-based fertilisers from fruit and vegetable waste in European and Colombian field trials

Introduction
Recycling of nutrients from fruit and vegetable waste in agriculture can reduce mineral fertiliser dependence and nutrient losses. In addition, the application of such bio-based organic fertiliser can increase the soil organic carbon content, beneficial for climate mitigation and soil health. Technologies as anaerobic digestion followed by microbial biomass production, insect breeding, pyrolysis and composting, can turn waste into respectively microbial biomass, insect biomass and frass, biochar and compost. These building blocks can be blended in various combinations, resulting in tailor-made bio-based fertilisers adapted to crop, soil and specific needs. After a first-stage verification of 15 fertilisers (blends) in laboratory incubation trials, a selection of fertilisers most suited to regional crop and conditions was produced at pilot scale and validated in field and greenhouse trials in Europe and Colombia.
Methodology
Field and greenhouse trials were performed in 5 regions: Flanders (Belgium), Almeria (Spain), Pays de la Loire (France), Friuli Venezia Giulia (Italy) and Valle del Cauca (Colombia). The bio-based blends, designed and adapted specifically for each region, were produced at pilot scale and applied on soil. Region-specific test crops were grown. The fertilisers were always compared with a reference fertiliser for that region, and sometimes a blank (no fertiliser addition). Several soil, plant and yield parameters (depending on the specific crop and region) were assessed in order to validate the fertilisers.
Results and discussion
In Flanders the Fl/1 and Fl/2 fertilisers increased the soil mineral nitrogen (N), especially in the soil layers accessible for the plant roots. The N gift associated with the fertiliser application rate of this trial was sufficient for the first crop (leek), but not for the relatively high N demanding second crop (cauliflower), with resulting lower yields and quality compared to the reference mineral fertiliser. However, Fl/2 application resulted in higher visual scores for leek and increased soil organic carbon and nitrogen. In Almeria, the Alm/2 and Alm/1b fertilisers were validated in greenhouse trials with tomatoes and cucumber. Both blends increased soil enzymatic activities, and Alm/1b increased soil N, organic matter and water retention compared to the reference organic fertilisers. The blends showed positive impacts on the oxidative stress, plant defence and tomato quality. The greenhouse and field trials in Pays de la Loire showed mixed results for the tested blends on soil, lettuce and grapes. In Friuli Venezia Giulia three blends were compared with a reference organo-mineral fertiliser and a reference manure in a grapevine trial. The bio-based blends increased the soil carbon content, N availability, microbial biomass and its activity and vine vigour. There were no differences in yield but, the quality of the must, derived from the grapes, was better for the blends compared to the references. In Valle del Cauca, the VdC/2 blend did not improve plant and fruit parameters for corn, bean and pumpkin compared to blank and mineral fertiliser, but there was a non-significant trend of improved physical, chemical and biological soil conditions after application of VdC/2.
In general, blends with larger shares of biochar showed better results compared to fertilisers with no of limited shares of biochar.
Conclusion
In conclusion, especially the soil quality was increased by the bio-based fertilisers. Effects on soil nutrient contents were diverse but can be altered by changing the fertiliser dose or composition (e.g. larger share of fast N delivering building blocks). In contrast to the lab incubation trials, biochar blends performed best in the field trials. Yield effects were less pronounced, and crop quality was sometimes improved. Longer field trials could assess the effect of multiple additions of the fertilisers and the long term impact on soil health and crop. The market, lifecycle and legal aspects of the implementation of the blends was tackled in parallel multi-actor analyses.