Estimation of Mineralizable Nitrogen from EQ Biosolids Products in an Urban Soil.

Accurate estimates of mineralizable nitrogen (N) from organic amendment addition is essential to improve nutrient management and agricultural productivity in urban agriculture. Mineralizable N has been generally estimated from N uptake by plants grown in a greenhouse or field, or from biological-based tests that determine the increase in soil inorganic N during incubation experiments. Because these tests are generally more time consuming and labor intensive, short-term incubations and chemical-based soil tests have been proposed to predict mineralizable N. The purpose of this field study was to quantify the amount of plant available N (PAN) provided by various new EQ biosolids products as estimated from tall fescue N uptake, and compare PAN obtained from N uptake to various biological and chemical tests for estimating potential mineralizable N (PMN) from EQ biosolids products used to amend an urban degraded soil. Inorganic N fertilizer was applied at four increasing rates (0x, 0.5x, 1.0x, and 1.5x agronomic N rate), and four EQ biosolids products were applied at an estimated 1.0x agronomic N rate. The EQ biosolids products were derived from blending with mulch, blending with sand and sawdust, thermal hydrolysis, composting, and thermal drying. Soil biological-based tests include a 7-day anaerobic incubation to measure changes in soil inorganic N over time, and the use of Solvita soil test to measure CO₂ emissions after 24 hours of aerobic incubation. Chemical-based tests consist of the analysis of total C, total N, C/N ratio, and water soluble C. The results of this study will be used to evaluate the PMN of different types of EQ biosolids products after their application to urban soils and will contribute knowledge of N availability of new EQ biosolids products that will help to improve urban nutrient management plans.