EFFECT OF MILL MUD AND GYPSUM AMENDMENTS AND THEIR COMBINATION ON PHYSICOCHEMICAL PROPERTIES AND HYDRAULIC CONDUCTIVITY OF MARGINAL SOILS

A SIGNIFICANT AMOUNT of sugarcane production occurs on marginal soils. Often these soils are sodic having severe physical and chemical constraints and poor water infiltration. These constraints limit the crop ability to access moisture and nutrients affecting the sugarcane crops production. The effects of treatment with either mill mud of different rates (120 t/ha and 20 t/ha) and/or gypsum as well as a combination of both treatments on the physicochemical, structural and hydraulic properties of soils were studied in the controlled, eight-month pot experiment. This was done using two different soil types collected from three depths (20 cm increments from the surface to 60 cm depth) in a sugarcane trial conducted in Maryborough. The soil was analysed to assess changes in pH, exchangeable cations, exchangeable sodium percentage (ESP) and spontaneous dispersion (Dsp). The effect of treatments on the saturated hydraulic conductivity (Ks) of repacked soil columns was studied by percolating deionised water through the soil columns with three wetting, draining and drying cycle to simulate infiltration of the soil with rain water. The two soils exhibited an increase in Ks following all treatments at all three depths, with the highest Ks in the soils treated with a combination of mill mud and gypsum. Dsp was substantially reduced relative to the untreated soils, under mill mud and gypsum combination treatments, following by gypsum and mill mud at different rates. Soil clay content and soil depth influenced the degree of the decrease in Dsp and ESP % and the increase in Ks. There was a significant correlation between ESP% and Dsp, R2=0.93. There were no noteworthy differences between the rates of mill mud (120 t/ha and 20 t/ha) were observed. The results indicate that incorporation of a mixture of mill mud and gypsum (20 t/ha and 6 t/ha respectively) could be the best and most labor economic method for improving properties and permeability of marginal soils.