Compost Improves Urban Soil and Water Quality

Construction in urban zones compacts the soil, which hinders root growth and infiltration and may increase erosion and degrade water quality. The purpose of our study was to determine whether planting prairie grasses and adding compost to urban soils should partially mitigate these concerns. We simulated construction activities by removing the topsoil, and compacting the soil by repeatedly driving over it with a tractor. Additionally, treatments included three compost application methods (compost and aeration, rototill and compost, surface compost). Plots were subjected to simulated rainfall applied using overhead sprinklers at a rate of 65 or 72 mm∙h−1. Bulk density was significantly reduced in surface soil where compost had been added. Compost plus prairie grasses resulted in significantly faster infiltration (63 vs. 52 mm∙h−1), slower runoff (4 vs. 25 mm∙h−2), less soil loss (25 vs. 119 kg∙Ha−1∙h−1), and reduced loss of ortho P (57 vs. 410 g∙Ha−1) compared to plots planted with bluegrass (Poa pratensis L.). A 5 to 7.5 cm thick compost blanket reduced time to runoff (60 min) compared to no compost addition (9 min). Topsoil addition without compost did not develop dark surface soil. Compost additions are recommended to reduce negative effects of urban compaction. Over time, the depth of compost additions decreased, necessitating further additions.