Managing Alkaline Toxicity

Including: Aluminium and Carbonate Toxicity and Nutrient Deficiencies

Alkaline soils (pH >= 8) occupy 23.8% of the land area in Australia. In southern Australia, approximately 8 million hectares are alkaline, comprising Calcarosols, Vertosols and duplex soils. Over 80% of soils in the cereal zones of South Australia have high pH in the subsoil (20-60 cm depth), ranging between 8.5 and 10 . High alkalinity adversely affects agricultural crop productivity. As part of GRDC project UA 00092 "Chemistry and crop agronomy in alkaline cropping soils" problems in soils associated with alkaline pH such as poor soil structure, phytotoxicity due to aluminium and carbonate species and, deficiencies of nutrients such as P, Ca, and Fe profoundly affected root growth and crop production. Field observations in South Australia (as well in northern India) have shown that wheat yield reductions of more than 50% occur when the soil pH is greater than 9.2. In this project it was found that above pH 9.2, negatively charged Al species and carbonate species dominate soil solutions and drastically reduce root growth. Studies on alkaline buffering capacity (resistance to change in the pH) of these soils have revealed that a high buffering action occurs only below pH 8 due to the prevalence of calcite minerals. On the other hand, reduction of pH from 10 to 8 occurs without any buffering effect. Therefore, a key conclusion from the research in this project was that if the soil pH is reduced below 9 by injection of protons (H+ or acid ions) through soil amendments and use of suitable plant species, crop productivity can be maintained in alkaline soils. After comparing several amendments such as manures, molasses, glucose and gypsum in addition to growing legumes, application of gypsum and growing of legumes were found to be the most efficient and practicable means of reducing the soil pH to below pH 9.

The relationship between soil pH(1:5 soil:water) sampled between 30-40cm and grain yield of Tamaroi (wheat) (adapted from Cooper 2004).

To assess the economic value of remediation of your alkaline soil use this theoretical Economic Calculator.

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