Effects of gypsum and stubble retention on the chemical and physical properties of a sodic grey Vertosol in western Victoria

The effects of gypsum (0 and 10 t/ha) and stubble management [retained (SR) or burnt (SB)] on a range of soil chemical, physical, and micromorphologic al properties were investigated on a grey Vertosol soil near Natimuk, Victo ria, Australia. After 2.5 years and 3 winter crops, gypsum, and to a lesser extent the stub ble treatments, resulted in significant changes to the composition of the e xchangeable and soluble cations, and to soil physical properties. When gyps um was combined with SR, the beneficial effects of this ameliorant on soil properties were present in both the A and B horizons of the soil. When comb ined with SB, the gypsum treatments were only effective in the A horizon. Organic carbon levels in the A and B horizons were not significantly affect ed by the gypsum or stubble treatments. However, micromorphological evidenc e indicated that in the A horizon, biological activity was greater in SR pl ots than SB plots. Soil dispersion, penetrometer resistance, and bulk density were reduced in plots treated with gypsum compared with plots without gypsum. A stubble man agement effect was also present, showing lower dispersion scores, penetrome ter resistance values, and bulk densities in SR plots than SB plots. The available water holding capacity of the soil from Natimuk was significa ntly (P<0.05) higher in the gypsum-treated plots than in plots without gyps um. This effect was limited to the A horizon of the SB plots, but was appar ent for the A and B horizons of the plots treated with SR. The use of gypsum in combination with SR (and break crops) may improve soil physical and chemical properties at a greater depth than the use of gypsum with SB alone.