Fig. 4. Scanning electron micrographs of (a) Santana do Livramento Typic Calciudert, Rio Grande do Sul (RS), untreated; (b)–(d) Cruz Alta, RS, sandy Typic Hapludox: (b) untreated, (c) soil organic matter (SOM) leached, and (d) dithionite-soluble iron (Fe_d) leached; (e)–(g) Cruz Alta, RS, clayey Typic Hapludox: (e) untreated, (f) SOM leached, and (g) Fe_d leached; (h)–(j) Santo Ângelo clayey Typic Hapludox, natural forest: (h) untreated, (i) SOM leached, and (j) Fe_d leached; and (k)–(n) Santo Ângelo, clayey Typic Hapludox, under no-tillage: (k) untreated, (l) SOM leached, (m) Fe_d leached, and (n) detail of (m).