Waste4Soil is a European research initiative focused on transforming food-processing residues and other bio-based waste streams into safe, effective and locally adapted soil improvers. By working through Living Labs across different pedoclimatic regions and cropping systems, the project aims to support circular bioeconomy models while improving soil health, resource efficiency and the sustainable use of organic amendments in agriculture.

Within the agronomic work of Waste4Soil, a broad assessment was conducted to evaluate the effects of selected soil improvers on soil properties, biological activity, crop performance and nutrient dynamics. Soil samples from the Living Labs were analysed for a wide range of physical, chemical and biological indicators, including pH, electrical conductivity, soil organic carbon, nitrogen, phosphorus, potassium, labile carbon and nitrogen fractions, enzyme activities, soil respiration, microbial biomass, functional microbial genes and community-level physiological profiles. The results showed that the effects of soil improvers were highly site- and product-specific, reflecting differences in soil type, crop, climate, amendment composition and application rate.

Several amendments improved key soil health indicators. For example, compost- and biochar-based products increased soil organic carbon, labile carbon fractions, microbial functional diversity or enzyme activities in specific Living Labs, while other responses were neutral or dependent on local conditions. Additional experiments assessed nitrogen mineralisation, partial replacement of commercial fertiliser, crop performance and disease suppressiveness. Selected soil improvers were able to replace part of the nitrogen fertiliser without reducing lettuce biomass, while some biochar and protein hydrolysate products showed suppressive effects against the soil-borne pathogen Globisporangium ultimum. Long-term modelling further indicated that soil improvers may contribute to increased carbon and nitrogen stocks, particularly when products contain stable organic matter such as biochar-rich materials. Overall, the agronomic work confirms the potential of locally produced soil improvers to enhance soil health and support sustainable crop production, while highlighting the need for context-specific recommendations.