Use of compost and biochar for the improvement of the quality of urban soils in the framework of an exhibition with public participation

Abstract

In the framework of the exhibition “After the end of the world”, held by the Centre de Cultura Contemporània de Barcelona, an urban space was set up as the basis of the Environmental Health Clinic of the engineer and artist Natalie Jeremijenko. Participatory activities were organized in terms of improvement of environmental health, including the enhancement of the quality of the soil by the use of amendments. Urban soils frequently have a low quality that hampers vegetation growth. Several properties, e.g. compaction and water holding capacity (WHC), can be redressed by the application of amendments. In this context, a field experiment was developed to assess the adjustment of soil quality by the addition of compost (C) and biochar (B) to a poor urban soil. Aiming at public participation, a simple method to visualize the effect of these amendments in soil properties was set up to be carried out by the people attending the exhibition. In the field experiment, treatments included C, B and C + B at three different proportions each. The assessed parameters were bulk density, pH, humidity, WHC and organic matter content (OM). Bulk density showed a decrease for all the treatments, being more drastic at rising proportions of amendment. The alkaline pH of the soil was lowered by the addition of C and C + B, whilst B slightly increased it. WHC was determined following the set up method, which showed reliable differences between samples. The WHC showed a relation with the OM, explained by the increased retention of moist caused by organic matter. Humidity and WHC followed the same tendency showing an increase for all treatments applied, being the effect larger for C than for B. The applied treatments showed a tendency to the improvement of soil properties, with increasing benefits at rising proportions of amendment. The combination of biochar and compost might lead to a higher enhancement. Thus, the addition of amendments to the soil could result in more optimal conditions for vegetation growth in urban areas.