1 Department of Environmental Engineering, Technical University of Denmark2 Residual Resource Engineering, Department of Environmental Engineering, Technical University of Denmark3 Universidad Autonoma de Barcelona4 Centro Tecnológico del Mar – Fundación CETMAR5 Institute of Agri-food Research and Technology
Due to increasing compost use in agriculture, there is an urgent need to evaluate compost benefits and impacts versus other fertilizers. Here we review the recent progress made in the quantification of positive effects associated with compost use on land using life cycle assessment (LCA), an internationally recognised environmental tool. Nine environmental benefits were identified in an extensive literature review: nutrient supply, carbon sequestration, weed pest and disease suppression, increase in crop yield, decreased soil erosion, retention of soil moisture, increased soil workability, enhanced soil biological properties and biodiversity, and gain in crop nutritional quality. Quantitative figures for each benefit were drawn from the literature and classified into short-term: less than 1 year; mid-term: less than 10 years and long-term: less than 100 years. The review shows that 5–60% of the applied compost N is mineralized, depending on the time frame. Mineralisation ranges from 35% to 100% for P and from 75% to 100% for K. Carbon sequestration rates are higher in the short term, up to 40% of the applied C, decreasing over time to 16%. Impacts on crop yields vary from decreases of 495% to increases of 52%. Compost increases 29–63% soil aggregate stability, reducing 5–36% soil loss. Soil bulk density decreases of 0.7–20% after compost application, potentially increasing soil workability. Also, water holding capacity and plant available water can increase by 50% and 34% respectively. Data on compost impacts on soil biodiversity is scarce and restricted to microorganisms. Compost may decrease microbial diversity by 2% or increase it by 4%. Clear impacts are also observed on microbial biomass, of 3.2–242% increase after compost application, and microbial activity: 43–344% increase. For weed, pest and disease suppression, along with nutritional content increase, quantitative figures could not be provided, either because of lack of data or because the effects are very variable and depend on specific local conditions. For soil erosion and soil moisture content, effects could be quantitatively addressed, but suitable impact assessment methodologies were not available. Additional impact categories dealing with phosphorus resources, biodiversity, soil losses, and water depletion are needed for a comprehensive assessment of compost application.