Nutrient Availability and Quality Assessment of Exceptional Quality Biosolids Products.

Exceptional Quality (EQ) biosolids products have the potential to improve properties of urban degraded soils. However, before promoting their use on urban landscapes, it is necessary to assess their soil benefits and environmental impacts. The objective of this preliminary study was to compare the attributes of newly developed EQ biosolids products specially tailored for urban soil use with those of existing products for the purpose of identifying their capability to support germination and plant growth, as well as to quantify their plant available nitrogen (N) and phosphorus (P). Seven EQ biosolids products and an inorganic fertilizer control were applied at various rates to 15-cm diameter pots in a soybean and tall fescue bioassay to assess product quality and nutrient availability, respectively. The EQ biosolids products resulted from a variety of treatment processes such as heating, composting, and blending with complementary organic and mineral materials. The soybean bioassay revealed that EQ biosolids products applied at an estimated equivalent agronomic N rate sustain germination and plant growth, and show no evidence of phytotoxic effects. Tall fescue biomass and N uptake showed similar trends with the use of EQ biosolids products and an inorganic fertilizer applied at an agronomic N rate. These results suggest that our estimations of organic N availability from various EQ biosolids products were accurate. Heat-dried, blended, and composted EQ biosolids products were validated to have approximately 40%, 20%, and 15% organic N availability, respectively. The use of these EQ biosolids increased Mehlich-1 P concentrations in the soil. However, soil P saturation ranged between 20 and 30% for most products. The results show that EQ biosolids products can be used as fertilizers and soil conditioners to sustain seed germination and plant growth. The information obtained with regards to nutrient availability will be used to estimate the application rates for future field experiments.