High clay contents, dense soils, and spatial variability are the principal subsoil constraints to cropping the higher rainfall land in south-eastern Australia

Available soil information and unpublished data from soil survey indicate that high clay contents and high bulk density are the major subsoil constraints to crop growth in the high rainfall zone (HRZ) of south-eastern Australia. Seven high rainfall agroecological zones are proposed as sub-divisions of the region to focus future research and development. The HRZ is dominated by texture-contrast soils (69.9%) and soils with clay subsoil (89.4%) and high bulk density (mean 1.6 t/m3). Sodicity and acidity are also significant constraints to crop production in the HRZ. The physical limitations to root growth in the HRZ subsoils are best appreciated through the least-limiting water range concept and growth-limiting bulk densities. Management options and results of past research and intervention in soil loosening, drainage, raised beds, liming, and gypsum are reviewed. Climatic uncertainty raises questions about the future relevance of waterlogging as a constraint in the HRZ and confounds the development of reliable recommendations for engineering intervention.