This is the top 2 soil horizons from a Red Chromosol at Jamestown in the Mid North of South Australia. A clay bolus was formed from the top 8cm (on right of photo) and then from the next 12cm of soil (on left of photo). The soil friability is remarkably different due to the accumulation and degradation of organic matter, the clay concentration and the historical management. It is a powerful photo to show the value of organic carbon in farmed soils.
Bolus Over! Look at the effect of Organic Matter