Provided for non-commercial research and educational use only. Not for reproduction, distribution or commercial use. This chapter was originally published in the book Methods in Enzymology, Vol. 496 published by Elsevier, and the attached copy is provided by Elsevier for the author's benefit and for the benefit of the author's institution, for non-commercial research and educational use including without limitation use in instruction at your institution, sending it to specific colleagues who know you, and providing a copy to your institution’s administrator. All other uses, reproduction and distribution, including without limitation commercial reprints, selling or licensing copies or access, or posting on open internet sites, your personal or institution’s website or repository, are prohibited. For exceptions, permission may be sought for such use through Elsevier's permissions site at: http://www.elsevier.com/locate/permissionusematerial From: David D. Myrold, Jennifer Pett-Ridge, and Peter J. Bottomley, Nitrogen Mineralization and Assimilation at Millimeter Scales. In Martin G. Klotz and Lisa Y. Stein, editors: Methods in Enzymology, Vol. 496, Burlington: Academic Press, 2011, pp. 91-114. ISBN: 978-0-12-386489-5 © Copyright 2011 Elsevier Inc. Academic Press