The Influence of Fly Ash Application on the Sorption-Desorption of Phosphate on Raised-Bed Soil of Tidal Swamplands

The availability of phosphate (P) in soils generally is controlled by the sorption and desorption process of P ions by soil minerals. We examined the sorption and desorption of P on raised- bed soils of tidal swamplands applied with fly ash. Four different aged of raised-bed soils (3, 9, 16 and 27 years) was applied with 25 Mg ha(-1) fly ash, and incubated at the dark for 15 days, and a batch experiment was carried out following the completion of incubation for the measurement of sorption-desorption of P. Results of the study showed that P sorption to fly ash-added soils fitted very well to the Langmuir Equation (R-2 = 0.91.0.98), in which fly ash application increased the maximum capacity of soil for P sorption (Q(max)). Increasing the value of Q(max) might be attributed to the presence of aluminium and iron oxides containing in the fly ash increased the sites of fly ash-added soils for the P sorption. The amounts of phosphate released from fly ash-added soils ranged from 4.4% to 7.4% of sorbed P at the treatment of without fly ash addition. Fly ash addition to the soil significantly reduced the desorption of P. Results of this study imply the potential use of fly ash as waste material for improving P availability in the raised-bed soils of swamplands.