Mapping the transition from pre-European settlement to contemporary soil conditions in the Lower Hunter Valley, Australia

Abstract

The concept of soil security has been proposed with the dimensions of capability, condition, capital, connectivity, and codification of soil. However, it remains a challenge to accurately and efficiently assess the soil's capability and condition as a function of soil change. The idea of genoform and phenoform was proposed 20 years ago and recently revitalized. Herein, we were inspired by these concepts to develop a general approach and concepts of genosoils and phenosoils for distinguishing the soil changes within soil mapping units as affected by human activities. Across a 220 km2 district with a diversity in landforms, parent materials, and land use types, we generated maps of Pre-European (soil classes that existed prior to agricultural development) soil classes using a digital soil mapping approach. Based on the land use change, Pre-European genosoils and present genosoils and phenosoils were identified and mapped within each of the Pre-European soil classes. The measured topsoil (0–10 cm) and subsoil (40–50 cm) properties have shown differences between the present genosoils and phenosoils. By objectively calculating the distances between the present genosoils and phenosoils in a principal component space using a recently published comprehensive soil classification system, several present phenosoils displayed significant differences among several soil properties (distance >8% of overall distance) and were redefined as new genosoils. The approach has successfully mapped genosoils and phenosoils within Pre-European soil classes at the district scale and identified shifts between present genosoils and phenosoils. It showed potential in detecting areas of soil changes due to human activities. Future work is required to separate seasonal fluctuations from long-term variations in NDVI and improve land use classification using remote sensing data. The method developed here can be applied in areas without remnant vegetation to separate the soil condition from capability by gauging phenosoils against genosoils.