Fig. 9. Kriged contour diagrams of total N, NH₄–N, and NO₃–N in topsoil (0–0.15 m) across time at the abandoned feedlot site. In 1998, NO₃–N concentrations ranged up to 120 mg N kg^–1 soil. Figures are shown in consistent scale, but the sampling frame for inorganic N was expanded by 7.6 m in all directions in 2000 and 2001.