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Applied and Environmental Soil Science
Volume 2011, Article ID 190731, 7 pages
Research Article

Estimating Nitrogen Availability of Heat-Dried Biosolids

Washington State University Puyallup Research and Extension Center, 2606 W. Pioneer Ave Puyallup, WA 98371, USA

Received 14 December 2010; Revised 16 February 2011; Accepted 26 February 2011

Academic Editor: Robert Edwin White

Copyright © 2011 Craig G. Cogger et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


As heat-dried biosolids become more widely produced and marketed, it is important to improve estimates of N availability from these materials. Objectives were to compare plant-available N among three different heat-dried biosolids and determine if current guidelines were adequate for estimating application rates. Heat-dried biosolids were surface applied to tall fescue (Festuca arundinacea Schreb.) in Washington State, USA, and forage yield and N uptake measured for two growing seasons following application. Three rates of urea and a zero-N control were used to calculate N fertilizer efficiency regressions. Application year plant-available N (estimated as urea N equivalent) for two biosolids exceeded 60% of total N applied, while urea N equivalent for the third biosolids was 45%. Residual (second-year) urea N equivalent ranged from 5 to 10%. Guidelines for the Pacific Northwest USA recommend mineralization estimates of 35 to 40% for heat-dried biosolids, but this research shows that some heat-dried materials fall well above that range.