Clay and humus act like glue in soil aggregates containing larger particles making them stable.
However soils with high clay content may not be stable. If they have low calcium content the aggregates will break down if compressed when wet. This leaves a solid mass.
Sandy soils with low levels of clay or humus are unstable; the aggregates break down easily into their component particles under compression or cultivation.
Characteristics of soil types The best of all worlds. Structure is easily worked into crumb aggregates. Good CEC combined with good drainage and water holding capacity. Easy to work. Loam Quick to warm and cool. Drain freely, which makes them easy to work, but also prone to drought. Organic matter breaks down quickly. Very sandy soils can have unstable structures. Nutrients leach out as no CEC. Sandy soils Good water retention. Can be fertile. Easier to work. Unstable soil structure can lead to capping and water logging. Silt soils Warm slowly and cool slowly. High CEC so fertile. Retain high levels of water which can lead to working and drainage problems. Clay soils