as a thin smear on a finely graduated (1 1 cm) Petri dish. Starting from a fixed cell in the dish, all three color particles (yellow, blue and red) were counted under a dissecting microscope. Counting continued until the number of red sand particles exceeded 500, at which point counting of the remaining particles in the current cell was completed and no new cell was started. The proportion of blue or yellow sand particles to red in the sample was used as an indicator of the extent of soil mixing.