Fig. 2. Glucosamine concentrations (g kg^–1 soil) in soil of grassland ecosystems (), no-tillage agroecosystems () and conventional tillage agroecosystems (), and their relationship with percent clay content, mean annual precipitation (MAP), and mean annual temperature (MAT). Data were obtained from Amelung et al. (1999c) for the grassland ecosystems and from Frey et al. (unpublished data) for the agroecosystems (the latter data were not included in the regression).