AMELIORATION OF SOIL BY NATURAL PROCESSES

A number of "natural" processes and their roles in soil amelioration are discussed and some new results are presented. Drying of soil produces cracks which can provide paths of low resistance for root growth and also can produce fracture of aggregates as the clay matrix shrinks around rigid inclusions such as sand grains. Rapid wetting of soil can induce micro-cracks which can make the soil weaker and more friable and can also increase the penetrability of the soil by roots. Ageing of soil after disturbance increases its water stability and its ability to resist mechanical stresses. The binding together of soil by roots and fungal hyphae can also induce stability as can the exudates from roots and other soil organisms. Roots are particularly important because of the biopores which they leave when they decay. Biopores (comprising root channels and earthworm tunnels) can provide important pathways for root penetration of subsequent crops, and it is shown that they can result in significant yield increases. It is suggested that these "natural" processes can be developed and exploited as "modified natural" processes, and that a considerable potential exists for using them to improve our soils at a modest cost.