Craig Scanlan

Approximately 5 and 29% of soils used for crop production globally have a sand or gravelly subsoil. The proportion of cropping soils with sand subsoil is greatest in Africa and Australia and Oceania. The countries with the greatest area of soil with gravel subsoil used for cropping are India and China. Sand and gravel subsoils have a limited capacity to supply soil and water to crops. Sand subsoils by definition have low clay content and, as a result, low water and nutrient storage capacity. The capacity of gravel subsoils to store water and nutrients decreases as gravel content increases. Although crop roots can access water and nutrients from these subsoils, the depth of these resources and physical constraints to root growth limit the efficiency of their use. Sand and gravel subsoils can constrain root growth although the mechanisms differ. Root growth is constrained in sand subsoils by constraints that can develop under crop production: compaction and aluminium toxicity. The impact of gravel subsoils on crop growth depends upon the penetrability of the gravel layer by crop roots. For impenetrable gravel layers, the properties of the topsoil will have the greatest influence on crop growth. For penetrable layers, root depth or length decreases as gravel content increases. There is potential to adapt agronomic management to maximise production on soils with sand or gravel subsoils. Split applications of nutrients can minimise leaching risk. There is evidence that the constraints that develop on sand subsoils due to crop production can be ameliorated profitably.