Decompaction and organic amendments provide short-term improvements in soil health during urban, residential development

Abstract

Urban land use, characterized by intense soil disturbance for site development, is rapidly expanding across the globe. This disturbance can have long-lasting effects on urban soil ecosystem service performance (e.g., water infiltration, turfgrass growth, and carbon [C] sequestration). We established a unique, multistakeholder collaboration with a private land-development company, environmental advisory nonprofit organization, and research university to study residential development effects on soil health and the effectiveness of rehabilitation practices. More specifically, we tested the impact of five current, locally recommended soil rehabilitation practices implemented at early stages of urban, residential development. In a controlled, real-world setting, we tested five treatments—a combination of decompaction and organic amendment additions—after major soil disturbances of mass and fine grading (part of subdivision development). Specific treatments included (1) a business-as-usual (or control) with compacted subsoil and 10 cm loosened topsoil, (2) mechanically decompacted subsoil and 10 cm loosened topsoil, (3) biologically decompacted subsoil using a green manure (with tillage radish [Raphanus sativus]) and 10 cm loosened topsoil, (4) mechanically decompacted subsoil with 2.5 cm of loosened topsoil mixed with 2.5 cm compost, and (5) mechanically decompacted subsoil mixed with 2.5 cm compost and 2.5 cm loosened topsoil. After turfgrass was established in all plots, per typical practice for erosion control, we measured physical, chemical, and biological soil health properties at 0 to 15 and 15 to 30 cm depths. The tillage radish had little-to-no effect on any soil properties, likely due to poor establishment. Compost amendments increased soil organic matter (+43%), soil test phosphorus (+79%), and soil test potassium (+60%) mostly in the top 0 to 15 cm. Compost amendments had little effect on soil microbial biomass and activity (measured as decomposition); however, they did increase salt-extractable organic C in the top 0 to 15 cm (+220%). We found even stronger effects of mechanical subsoil decompaction, which increased infiltration rate by over 2,000% and time-to-runoff by 463%, on average, providing evidence that deep ripping subsoils improves water influx and reduces runoff from residential lawns. Decompacting subsoil and adding compost had clear benefits to physical and chemical soil health early in urban, residential development. We would recommend land developers use both practices for improving soil ecosystem services in the short term, and there may be longer-term benefits too.