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

Abstract

Abstract. Available soil information and unpublished data from soil survey indicate that high clay contents and high bulk density are the major subsoil constraints to crop growth in the high rainfall zone (HRZ)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/m 3 ). 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.

Changes in pasture root growth and transpiration efficiency following the incorporation of organic manures into a clay subsoil

“…These occupy large areas of the agricultural land in southern Australia and are characterized by a light-textured sandy, sandy-loam or loam soil, overlying dense clay subsoil (Chittleborough 1992). Root growth into the deeper layers of the clay subsoil is frequently limited by excessive soil density and strength, and low macro-porosity, and there can also be chemical constraints from salinity and sodicity in some duplex soils (MacEwan et al 2010). A feature of the physically constraining subsoil is that crop growth can be constrained by transient waterlogging in winter when rainfall exceeds evaporation, and then limited by water deficits as rainfall declines in mid to late spring.…”

Farming system context drives the value of deep wheat roots in semi-arid environments

“…As a result, the previous simulation studies may be overestimating the value of modified root systems for many Australian cropping soils. For example, sodicity constraints have been reported for 59% of Victorian and 63% of South Australian arable land ( Ford et al , 1993 ) and are estimated to affect more than 26% of Queensland ( Dang et al , 2006 ; MacEwan et al , 2010 ) and around 50% of arable land nationally.…”

Organic and inorganic amendments did not affect microbial community composition in the bulk soil differently but did change the relative abundance of selected taxa

“…• Changes in microbial community structure were due to movement of soil solution away from the amendment. Soils with dense, sodic clay subsoil dominate the dryland crop production zones of south-eastern Australia (MacEwan, Crawford, Newton, & Clune, 2010). These subsoils are naturally physically constrained and can severely limit plant growth by restricting root penetration and water use by plants (Adcock, McNeill, McDonald, & Armstrong, 2007;Zhang, Turner, Poole, & Simpson, 2006).…”