Capitulo de libro
THE EFFECT OF ORGANIC MATTER AND SOIL CHEMICAL PROPERTIES ON SULFATE SORPTION IN CHILEAN VOLCANIC SOILS
Fecha
2005Registro en:
1578083443
978-157-808-344-2
7020934
Institución
Resumen
Almost 70% of the volcanic ash-derived acid soils in Chile are deficient in plant available sulfur (S). Furthermore, the low organic matter mineralization rates in these soils necessitate regular application of S fertilizers to achieve sustainable production. It is therefore important to examine the effect of various factors that regulate the behaviour of this nutrient anion in these soils. The difference in sulfate sorption capacity between Chilean Ultisol and Andisol, which vary in organic matter content and natural acidity levels (pH, aluminium saturation), and the effects of different metal ions and phosphate on sulfate sorption were determined. Results indicated that sulfate sorption capacity for both soil types was strongly pH-dependent, with sorption decreasing with increase pH. Sulfate sorption was highest at pH 3.5 and decreased markedly as pH increased. However, the initial natural soil acidity influenced sulfate sorption, which was higher in highly acid soils than in low acidity soils; this was attributed to the higher contents of exchangeable Al and acidity of reactive sites in the former soils. Sulfate sorption was concentration dependent showing a significant amount of sorption even at pH 8.0 at high sulfate concentration (20 mM) in solution, while at low sulfate concentration (6 mM) in solution, sorption was almost zero at pH>6.5. Removal of fulvic acids (FA) and humic acids (HA) resulted in an increase in sulfate sorption in both soil types. Increase in sorption was more pronounced with the removal of humin fraction, whereby the PZC changed from 4.1 to 7.6 in the Andisol and from 4.0 to 8.3 in the Ultisol, indicating a large increase in positive charge at low pH. Sorption maximum ranged from 20 to 350 mmol kg-1 in the Andisol and 15 to 180 mmol kg-1 in the Ultisol, which was consistent with the greater increase in the number of active sites (Ns) in the former soil (from 80 to 600 cmol kg-1 in the Andisol and from 100 to 300 cmol kg-1 in the Ultisol). These results indicated a strong reaction between sulfate ions and active surface sites on inorganic minerals, such as allophane and ferrihydrite in Andisol. There was a significant effect of metal cations on sulfate sorption; the latter followed the order Ca > Mg > K, which was consistent with the hydrated ionic radius of these metal cations. Results from the competitive sorption study indicated that while sorption of phosphate was not affected by the presence of sulfate ions, sorption of sulfate was greatly inhibited by the presence of phosphate ions.