EVALUATION OF 2 COAL-DERIVED ORGANIC-PRODUCTS IN AMELIORATING SURFACEAND SUBSURFACE SOIL ACIDITY

Acidity in the soil surface and subsurface is of major concern in hort iculture, cropping and pasture production systems in southern Australi a. Broadcast applications of lime to the surface have proved to be ine ffective in ameliorating subsurface acidity in the short term. Two cal cium-saturated coal-derived organic products, an 'oxi-product' (OXPR) and an 'oxi-fulvate' (OXFU), were evaluated for use as liming material s with specific consideration given to amelioration of subsurface acid ity. The effects of these two organic products and of lime on the chem ical composition of the A(1) and A(2) horizons of an acid red podzol w ere investigated in leaching columns, 20 cm long. OXPR and OXFU supply ing 80 or 160 g Ca m(-2) were compared to 160 g Ca m(-2) applied as Ca CO3 and a control receiving no amendments. The effects of CaCO3 on exc hangeable Al and pH were limited to the surface 2 cm. In contrast, the two organic amendments were effective in decreasing exchangeable Al a nd increasing pH and exchangeable Ca to depth, the extent being a func tion of amendment and rate applied. The formation of inorganic and org anic complexes were assumed to be responsible for the movement of Al o ut of the column in the leachate, although significant quantities of A l were precipitated in the column. Significant linear regressions were observed between the ionic strength and Al in the leachate. Significa nt quantities of Mg and K were displaced by Ca and leached from the co lumn; consequently, this loss must be considered against the benefits of decreased exchangeable Al when assessing fertility for plant produc tion.