Quality of bio-based fertilizers is decisive for improving soil quality in Europe – A meta-analysis

Summary in the original language of the document

Organic matter is a vital component of soils and decisive for soil health and sustainable food production. Agricultural soil use often decreases soil organic matter stocks and climate change may aggravate the situation, utting food security and ecosystem functioning at risk. Bio-based fertilizers (BBFs, most often waste or residue-derived) are a vital part of future circular economies ocussing on closed nutrient cycles in food production and agriculture. It is unclear if BBFs have positive effects on soil organic carbon (SOC) because studies on BBFs were so far mostly focussed on plant nutrition and ran mainly as short-term pot experiments. We filtered, extended and reclassified the comprehensive meta-analysis of Chen et al. (2018) to elucidate the effects of bio-based fertilizers on SOC concentrations in European and North American long-term experiments. The revised data set consisting of 260 observations from 60 field trials (now including a minimum duration of 5 years) showed significant effects of BBF quality on SOC concentration when compared with minerally fertilized plots and elucidated the role of soil and site properties on the efficiency of BBFs to increase SOC. The extended data set showed that solid and carbon-rich BBFs were most efficient in increasing SOC concentrations. Less developed soils and loamy soils in dry climates showed the highest potential for carbon equestration through BBF application. We stress the importance of carbon inputs for the maintenance of current SOC concentrations, thus demanding the cautious use of C-depleting steps during BBF processing, only to be applied if elimination of organic pollutants and pathogens is needed.