Amelioration of alkaline phytotoxicity by lowering soil pH

Highly alkaline soils (pH >9) may adversely affect agricultural crop productivity. At pH >9.2, aluminium (Al) phytotoxicity may further retard plant development. Most alkaline soils have little alkaline buffering capacity, making it feasible to use acid to lower soil pH to <9.2. Many methods of lowering soil pH have been trialled; however, little research has been done on their relative effectiveness and longevity. Methods trialled in this study as means of lowering soil pH were chemical additives (gypsum), organic additives (glucose, molasses, horse manure, green manure, humus) and leguminous plants. Gypsum was also used in conjunction with plants to determine any synergistic effects of combining treatments. All ameliorants trialled except humus and horse manure proved effective at lowering soil pH to <9.2. The reduction achieved with biological amendments was temporary, with pH returning to pre-amendment levels over the course of the study. Gypsum was most effective amendment for lowering soil pH and sustaining the lowered pH level. The use of plants to lower soil pH, in conjunction with gypsum to sustain the lowered pH, may be an effective and economic method of remediating Al phytotoxicity in alkaline soils.