http://www.ipm.iastate.edu/ipm/icm/taxonomy/term/6041/feed The taxonomy view with a depth of 0. en http://www.ipm.iastate.edu/ipm/icm/2005/10-10/ntest.html John Sawyer and Ali Tabatabai explore this question. Ali Tabatabai IC-494(24) -- October 10, 2005 John Sawyer Nitrogen Soils Thu, 13 Oct 2005 10:54:19 -0500 jvandyk 218 at http://www.ipm.iastate.edu/ipm/icm