Organic amendments alter urban soil microbiomes and improve crop quality

Urban agriculture has the potential to support the health and sustainability of urban communities across the globe. Nonetheless, little information is available on urban soil management and strategies for supporting different aspects of soil health in the context of urban farming. We performed a greenhouse trial to investigate the effects of a variety of organic amendments derived from local municipal waste products on the soil microbiome as well as tomato (Solanum lycopersicum, L.) productivity and quality in an urban agricultural soil from the San Francisco Bay Area (USA). We hypothesized that organic soil amendments could enhance microbial abundance, activity, and diversity in urban soils, however the specific effects may be dependent on the physicochemical and biological properties of the amendments used. Further, we hypothesized these shifts in soil biology could correspond to changes in crop productivity and quality. Liquid food waste hydrolysate and mixed herbivore waste compost increased microbial abundance in the soil compared to mineral fertilizer, likely due to increases in available carbon and nutrients. Analysis of potential extracellular enzyme activity showed solid amendments could enhance microbial carbon cycling in the soil as a result of increases in organic matter. 16S rRNA sequencing indicated that solid amendments altered the composition of the soil microbiome, including the relative abundances of dominant soil bacterial phyla. Mineral-fertilized tomato plants generally had higher productivity and yields compared to plants grown with amendments, but plants treated with the hydrolysate and mixed herbivore waste compost had enhanced fruit soluble sugar content (i.e., °Brix). This study documents significant effects of diverse amendments derived from local municipal waste products on microbiomes found in urban soils. Further, the data suggests linkages between soil management, soil biology, and crop taste, which should be explored in future research.