ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 52 Number 4
Influence of drainage on pH, sulphate content and mechanical strength of a potential acid sulphate soil in Fiji
The development of acid conditions in potential acid sulphate soils is attributed to the oxidation of sulphides to sulphates following reduction of the pore pace saturation as a consequence of drainage. A study was made to evaluate the changes in pH, sulphate content and mechanical strength at matric potentials and degree of pore space saturations which accompany small departures from waterlogged conditions. The results show that characteristic decreases in pH and increases in SO4-S develop rapidly when the degree of pore space saturation fell below 0·95 which in this soil was associated with a matric potential of about - 60 cm of water. The initial oxidation process appeared to be determined by the oxygen diffusion coefficient of the soil associated with the degree of pore space saturation and soil matric potential. Estimates of bearing capacity indicate that this soil could support mechanical equipment associated with agricultural operations at matric potentials between -50 and -80cm of water. Management of this soil to minimize oxidation would, however, restrict the soil water regime to matric potentials greater than 60cm of water.