Assessment of EQ Biosolids Products for Urban Gardens.

Exceptional Quality (EQ) biosolids may be developed into products that can rehabilitate disturbed urban soils for the production of vegetables in urban gardens. The objectives of this study were to investigate the effect of various EQ biosolids products on vegetable plant yield and the provision of ecosystem services (i.e. improving soil physiochemical properties and water quality) to urban degraded soils. Three EQ biosolids products derived from different treatment processes (thermal hydrolysis, composting, and blending with complementary organic materials) were applied at the agronomic nitrogen (N) rate and at a disturbed land reclamation rate (5x agronomic N rate). An inorganic fertilizer control and a pelletized, heat-dried EQ biosolids were applied at the agronomic N rate only. Fall 2016 vegetable production revealed that the application of EQ biosolids at rates higher than the agronomic N rate may be most beneficial to obtain greater yields in urban degraded soils. Nitrate (NO₃-N) in leached water increased right after amendment and inorganic fertilizer applications; however, NO₃ loss (lbs NO₃/ac) throughout the fall (2016) and early spring season (2017) was not significantly different between the addition of inorganic fertilizer and biosolids treatments. Ammonium (NH₄-N) and ortho-phosphate (PO₄) concentrations were found to be below detection limit during the entire growing season, which indicates that EQ biosolids products had little contribution to NH₄-N and PO₄ loss. Soil Phosphorus Saturation Ratio (PSR) revealed that all treatments had PSR values below 20%, suggesting that the EQ biosolids products used in this experiment are not a strong source of bioavailable P. High iron concentrations of EQ biosolids could have reduced P availability. Hence, higher EQ biosolids application rates for urban agriculture might not result in significantly higher nutrient losses, and the benefits of these amendments on soil properties and plant growth could justify their higher applications to urban, low fertility soils.