Effects of potassium humate on aggregate stability of two soils from Victoria, Australia

The potential for using commercially available potassium humate (K-humate) derived from Victorian Brown Coal to improve soil structure and aggregate stability was assessed in this study. Laboratory experiments were conducted on two agricultural soils from the southeastern and northern parts of Victoria, Australia. Bulk surface soil (0-15 cm) samples of an acidic soil (pH 4.6) from Dixons Creek in the Yarra Valley (DeBortoli Vineyards) and an alkaline sodic soil (pH 8-9) from North Mooroopna (waste water irrigated site under grazed pastures) in the Goulburn Valley were evaluated for any changes in aggregate stability after treatment with various application rates of K-humate and subjection to a series of wetting and drying (W/D) cycles. On each soil, six rates of K-humate (0, 0.05, 0.10, 0.50, 1.00, and 10.00 g/kg of soil) were applied, and four sequences of wetting and drying cycles (0, 3, 7, and 10 cycles) were carried out using the 2-5-mm aggregate size fractions. Mean-weight diameter (MWD) of the treated samples was determined after wet-sieving and drying. Compared with the controls, K-humate-treated samples showed significant improvement in MWD for both soils, although treatment did not prevent some decline in MWD after seven wetting/drying cycles. Low treatment rates gave significant improvement for the acidic soil; however, rates of 1.0 g/kg and above were required for significant improvement for the sodic soil. This work demonstrates that potassium humate is potentially effective as a soil conditioner in improving aggregate stability of acidic and sodic soils against adverse effects of cyclic seasonal wetting and drying conditions. (c) 2004 Elsevier B.V, All rights reserved.