Effect of value-added organic co-products from four industrial chains on functioning of plant disease suppressive soil and their potentiality to enhance soil quality: A review from the perspective of a circular economy

The virtuous reuse in-situ of agri-based organic wastes to produce compost and bio-organic fertilizer in the farm for increasing natural suppressiveness of soil to soil-borne plant pathogens has been a better way for longer time for designing new sustainable cropping systems without using chemical fumigants. Nevertheless, many others co/by-products provided by the biodiesel supply chain (oil-less seed meal/cake/pellet), biopolymer/biocomposite industry (chitin/chitosan) and processing plants for wastewaters depuration (biosolid/sewage sludge) integrated or not with biogas production (anaerobic digestate) are still too under-explored, though of great interest to increase disease suppression of soil. This work aims at covering this lacking of information in the review literature giving recent outcomes on the main effects and potential impacts of these organic inputs on interaction among the beneficial microbial consortia involved in disease suppression with the crop-pathogen systems of major economic impact. The paper first introduces the main sources, characteristics and application fields of the co-products aforementioned. Afterwards, it describes and discusses the main ecological effects of these organic inputs on functioning of disease suppressive soil under the perspective of microbiome disturbance. Then, it analyses and critically discusses the potential impacts of such value-added co-products on soil quality taking into account the main fertility parameters. Finally, how the resulting points of strength and of weakness can drive the progress of a sustainable management of soil for its quality, fertility and plant health are discussed from the perspective of a circular economy approach according to the "Green Deal" policies launched by the European Union. From this review work it turned out that such co-products have great potentiality to increase soil suppression and to improve soil quality as the benefits overall outweigh the drawbacks, though they may give sometime inconsistent disease control. For these reasons, their practical applications as soil amendments are still strongly limited at the field conditions.