Fig. 3. Results of amplitude sweep tests with predrained (at –60 hPa) samples of (a) a sandy and (b) a clayey Typic Hapludox from Cruz Alta, (c) a clayey Typic Hapludox, Santo Ângelo, under natural forest, and (d) a clayey Typic Hapludox, Santo Ângelo, under no-tillage conditions. G' = storage modulus, G'' = loss modulus, = shear strain, SOM = soil organic matter, Fe_d = dithionite-soluble iron.