Subsurface Soil Acidification in Farming Systems: Its Possible Causes and Management Options

Abstract

Subsurface soil acidity is widespread and its amelioration is costly and often practically infeasible. This paper summarizes recent research on the causes and management of subsurface soil acidity in farming systems. The development of subsurface soil acidity depends largely on acid production by plant roots due to excess cation uptake, particularly under legume-based agriculture. The deposition and decomposition of plant residues do not cause subsurface soil acidification but contribute to the development of subsurface soil acidity profiles through their liming effect on the topsoil. Nitrification from ammonium-based fertilizers or from organic N in plant residues, and subsequent leaching of nitrate, contribute mainly to topsoil acidification. In contrast, the uptake of leached nitrate and denitrification in deeper layers may decrease subsurface soil acidity. Various application methods and liming materials have been studied for their effectiveness in ameliorating subsurface soil acidity. These include application of lime, gypsum and organic materials, and growing acid-tolerant crops. Biological amelioration through managing excess anion (nitrate) uptake has been tested in the field and is a promising method to ameliorate subsurface soil acidity. The major challenge for the biological amelioration method is to synchronize nitrate movement and root capture in the subsurface soil for maximal alkalization and minimal nitrate leaching loss.