Subsoil Acidity Amelioration for Improved Soil Productivity

Subsoil is the layer (stratum) of earth immediately below the surface soil (below 20 cm), consisting predominantly of minerals and leached materials such as iron and aluminium compounds. A favourable condition of subsoil is important for improved productivity of deep-rooted crops like maize, sorghum, soybean etc. Any physical, chemical or biological characteristic of the soil located below the seedbed that limits the ability of crops or pasture to access water and nutrients is considered as a constraint to the subsoil. Subsoil acidity characterized by low Ca and high Al at depths below the plough layer, constrains crop productivity all over the world, especially in the highly weathered acid soils of the humid tropics. Yield reduction due to subsoil acidity results from high concentrations of soluble Al, Mn etc. or low plant-available calcium or magnesium in the root zone, inhibiting physiological and biological activities, root development and uptake of nutrients as well as water. Aluminium toxicity in the subsoil is the major growth limiting factor associated with subsoil acidity. Research findings suggest that conventional surface liming has very little effect on subsoil acidity. Therefore, successful amelioration of acidity in the subsoil requires specialised management practices involving application of soluble sources of calcium or magnesium or improving the solubility and downward movement of liming materials by the application of organic amendments like biochar. This paper attempts to analyse the impacts of subsoil acidity on soil productivity and its mitigation strategies.