Predictive relationships between pH and sodicity in soils of tropical Queensland

Abstract

Interrelations between soil pH and exchangeable sodium percentage (ESP) were examined using soils from the Burdekin River area in tropical Queensland. Highly significant correlations were found but the goodness of fit differed between groups of soil profile classes. In general, Typic Natrustalfs of the flood plains had better relationships (r² = 0.85) between these soil properties than did the Chromusterts (r² = 0.50). The regression ESP = 1.935 × 10^‐5 _pH6.205 (_r2 = 0.61; n= 288) for all soils and depths underestimated ESP in Typic Natrustalfs groupings and overestimated this soil property in the Chromusterts.

By using the appropriate regression, pH levels associated with non‐sodic, sodic and strongly sodic horizons have been defined. Either laboratory or field determined estimates of pH may be used but the laboratory determined value is preferred. It is expected the predictive models will remain valid until soil ESP or pH levels are significantly modified as a consequence of agricultural development.

Key words:

• Soil pH
• Sodicity (ESP)
• Soil analysis
• Burdekin River
• Queensland