CHEMICAL-PROPERTIES OF ASH DERIVED FROM EUCALYPTUS LITTER AND ITS EFFECTS ON FOREST SOILS

The concentration of elements in ash from eucalyptus litter varied several-fold depending upon the type of fuel and combustion conditions. In vegetation fires, and where ash is used as a soil amendment, significant amounts of nutrients and heavy metals will be added to soils. Three patterns of dissolution of ash constituents in water were observed: (1) high (> 70% of element content of ash quickly soluble), but with a residual component which was not solubilized by further dilution (elements K, S, and B); (2) relatively insoluble, but where the amount dissolved is related to dilution (Ca, Mg, Si and Fe), and (3) highly insoluble (such as P). The capacity of ash to neutralize acid was well correlated with the total amount of basic cations (K + Ca + Mg) in the ash. Addition of 4-20 t ash ha(-1) to a range of forest soils increased pH (KCl) by one to three units depending on soil C content, decreased exchangeable Al and H content, increased exchange sites (variable negative charges) and increased basic-cation levels. Ash addition increased respiration rates in all soils, especially in those with higher organic matter content. Addition of ash increased N mineralization rate and nitrification in most of the soils, although the magnitude of response was not clearly related to assessed soil properties. This study suggests that account must be taken of soil and ash properties when assessing the utility of plant ash for soil amelioration.