Aggregation of Sodic Subsoils Using Gypsum and Decomposable Phyto-organics: Interactions and Implications for Bauxite Red Muds

Abstract

The ability of gypsum with or without the addition of N-rich decomposable phyto-organics to increase soil aggregation in sodic subsoils was examined. Before flowering, young leaves from Vicia sativa (common vetch) were finely chopped to <2 mm particles and incubated into the subsoil at 80 % field capacity for 12 weeks. Experiments were carried out on two alkaline sodium affected sub-soils (15–30 cm) from Strathalbyn, and Two Wells in South Australia, under glasshouse conditions in pots containing 1 kg of soil. To a sodic subsoil, rapid encrustation was induced to a depth of 8 mm. The average size of dispersed materials in control soils was < 5 µm, whereas after green manuring, the average particle size increased up to 30 µm. Such particles were insufficient to resist translocation by light to moderate winds. The products of the released Ca²⁺ from native lime aggregated the clay particles and stabilized them into masses which exceeded 100 µm in diameter. The results of this study promise the use of gypsum as an ameliorant for sodic alkaline environments such as the red muds of bauxite mine-spoils. Where no organic matter had been added, it is concluded that the binding action of Ca²⁺ released in solution replaced the Na⁺¹ which had been dispersing the particles prior to the treatment.

Original article: Sodium affected subsoils, gypsum, and green-manure: Inter- actions and implications for amelioration of toxic red mud wastes. Environmental Geology Volume 45, Issue 8, pp. 1118–1130.