Effects of coal derived humic substances on water retention and structural stability of Mediterranian soils

The potential for using coal-derived humic substances to improve the available water holding capacity (AWC) and aggregate stability of typical Mediterranean soils was evaluated in the laboratory using an agricultural surface (0-20 cm) soil from each of three regions of Italy, (Sicily, Tuscany and Venetia) and five rates of humic acids (HA), 0,0.05, 0.10,OSO and 1.00 gikg.There were significant ( P < 0.05) differences between the field capacity (FC), permanentwilting point (PWP), and available water capacity (AWC)values ofthe controls and those treated with 0.05 gikg of the HA. Beyond this rate, differences in these properties were not significant. At the 1.00 gikg HA rate, the relative improvements in AWC over the three controls were 30%, 10% and 26O/o. Low rates (0.05 to 0.10 gikg) ofHAwere also needed to obtain a 40 to 120% improvement in aggregate stability ofthese soils relative to the controls. These results indicate that the addition of highly humified organic matter such as coal-derived humic substances can improve the structural and water retention properties of degraded arable soils. However, since there is not yet any direct evidence that these humic materials can ameliorate soils under field conditions, field studies will be needed to validate these results.