Biosolids Improve Urban Soil Properties and Vegetable Production in Urban Agriculture

Abstract

Core Ideas: Biosolids amendments improved degraded urban soil properties. High biosolids application rates showed greater potential to increase vegetable yield. Large amounts of soil carbon accumulated (37–84%) two years after biosolids additions. Exceptional quality (EQ) biosolids may be used to rehabilitate disturbed urban soils for vegetable production in urban gardens. The objectives of this study were to investigate the effects of various EQ biosolids products on urban soil properties and vegetable yield. Field research was conducted at Blacksburg, VA, in an urban subsoil fill from a nearby construction site. Three EQ biosolids products were applied biannually at agronomic nitrogen (N) rates (fall 2016–2017, and summer 2017–2018) and annually at land reclamation rates (5× agronomic N rate; fall 2016–2017). A heat-dried and pelletized EQ biosolids product and inorganic fertilizer were applied biannually at agronomic N rate only. Biosolids increased soil C storage vs. the control by 37 to 84% after 2 yr. Soil N availability was less than expected based on previous greenhouse research even after cumulative biosolids rates. Lower N availability likely was due to low organic matter and high clay concentrations that reduced organic N mineralization. Cabbage [Brassica oleracea L. var. capitata L.] (∼3.1 kg m–2) and Siberian kale [Brassica napus L. subsp. napus var. pabularia (DC.) Alef.] (∼1.1 kg m–2) yields were greater with reclamation rates than with the inorganic fertilizer (1.0 kg m–2 and 0.4 kg m–2, respectively) in fall 2017. Despite limiting soil physicochemical conditions, biosolids addition at reclamation rates showed greater potential to increase vegetable yield after 2 yr of application.