AN ALTERNATIVE METHOD TO MEASURE AVAILABLE SULPHUR BY ION CHROMATOGRAHY IN VOLCANIC SOILS

Abstract

Sulphur (S) is an essential crop nutrient, and its deficiency in the soil has been reported in recent years. The index of S fertility is based on the sulphate availability measured by the turbidimetry method (TB), because it is easily and quickly applied. However, this method has shown a large variability, and lack of precision to determine sulphate, particularly in Andisols, so S fertility assessment in this type of soil is not certain. The objective of this study was to evaluate the applicability of the ion-chromatography method (IC) to obtain more accurate and precise results of the available S in volcanic soils of Chile. Two sites contrasting soil and climate conditions were assessed in their available sulphate content by the TB and IC methods The IC method was tested for accuracy and precision by calculating the curve of calibration and by comparing sulphate in the soil extracts (n=10) with the addition of standard concentrations to the same extracts. Values of available S in the Andisol varied depending on the methodology used (P < 0.05), whilst no differences were observed in the Inceptisol (P > 0.05). The IC showed linearity (R2 = 0.9998) and precision, with no significant differences between the measured and modelled value of sulphate (P > 0.05). A wide range of available S was found in others sites (7-37 mg SO4 -2 kg soil-1), which highlights the extend of available S in Andisols and the relevance of an appropriate methodology for the interpretation of the S balances in these soils.