Radical soil management for Australia: A rejuvenation process Alex McBratney, Tony Koppi, Damien J. Field ⁎ Centre for Carbon, Water and Food, Faculty of Agriculture and Environment, University of Sydney, New South Wales, Australia abstract article info Article history: Received 21 July 2015 Received in revised form 2 February 2016 Accepted 3 February 2016 Available online 4 February 2016 Particularly in the Australian context, this concept paper argues that much of the continent has highly weathered soil of great antiquity with poor agricultural productivity, that much younger soil also exists in juxtaposition, and that certain anthropogenic processes, such as soil inversion or any other radical soil management, can rejuvenate soil for increased productivity. Younger soil occurs wherever there is an accumulating environment where rela- tively young materials are being deposited (e.g., alluvium), or eroding circumstances where less weathered ma- terials become exposed such as following colluvial or deflation activity. Depositional materials are not necessarily younger when they result from redistribution of highly weathered materials such as by aeolian activity. Certain soil types may be considered as self-rejuvenating if they exhibit self-mulching and pedoturbation characteristics whereby less weathered subsoil material is brought up into the soil. Soil rejuvenation events, through a variety of processes, therefore occur naturally in Australia, as they do elsewhere. With respect to wheat production for il- lustrative purposes, it is argued that young or rejuvenated soil is more agriculturally productive, and that certain anthropogenic processes (such as the addition of clay or bringing subsoil clay to the surface) that rejuvenate soil can be brought about by radical soil management. © 2016 Elsevier B.V. All rights reserved. Keywords: Alfisols Vertisols Aridisols Soil management Soil rejuvenation Soil aging processes Tillage 1. Introduction Australia has the reputation of having very old and highly weathered soil (Grant, 2007; Price, 2010) in a landscape of great antiquity (Taylor, 1983; Twidale, 2007; Twidale and Campbell, 2005). Taylor (1983); Beckmann (1983) and McKenzie et al. (2004) note the widespread infertile nature of Australian soil associated with prolonged deep weathering. This poor fertility of Australian soil can partly be attributed to a lack of the kinds of rejuvenation processes that occurred in Europe and North America, such as Pleistocene glaciation (Taylor, 1983; Twidale and Campbell, 2005) which removed much of the older soil. However, Australia has also had some rejuvenation episodes such as tertiary volcanic activity particularly in the eastern part of the conti- nent (Green, 1969; Beckmann, 1983; Twidale and Campbell, 2005) that has contributed younger soil materials by their weathering and redistribution. Many soil-forming processes that occur within soil profiles have been identified (17 by Bockheim and Gennadiyev (2000)) and Table 1 categorizes high-level processes within and external to the profile that age and rejuvenate soil. Aging processes include those that remove ele- ments or materials from the soil either vertically downwards or lateral- ly. While some elements (e.g., salts) may move upwards, such a process is not necessarily aging even though it may be symptomatic of land management (clearing and irrigation) in an old weathered landscape (Isbell et al., 1983). Accretion materials such as alluvial, lacustrine, collu- vial, estuarine and wind-blown deposits represent the redistribution of materials (possibly from a younger source) and rejuvenation processes. Another natural in situ rejuvenation process in swelling soil types is given by self-mulching shrink-swell clays where subsoil material may gradually be brought to the surface. Australia therefore has a range of weathered soil materials, from the ancient relatively infertile to relative- ly young that subsequently influences agricultural production. Recently, the rate of soil formation by conversion from consolidated parent material has been estimated as a global average of 114.27 ± 10.93 mm kyr -1 or about 0.1 mm per year (Stockmann et al., 2014). This conversion rate does not indicate the rate of profile differentiation, such as the development of clay rich subsoil or leaching rates. Given the appropriate conditions of soil formation and parent mate- rial composed of a mixture of sand and clay (as opposed to all clay or all sand), a consequence of soil aging is the tendency for the soil to become more texturally differentiated and duplex (as first defined by Northcote (1960)) over thousands of years (Walker, 1962; Chittleborough, 1992), and to exhibit many of the constraints listed above. The rate of differen- tiation of a duplex profile in an unconsolidated parent was estimated as greater than 10,000 years (Walker, 1962) and given as from 10 3 years to 10 6 years by Walker (1989). The aging sequence of textural differentia- tion is depicted in Fig. 1 with indicative dates given based on Walker (1989). A rejuvenated soil is one where the effects of aging through geolog- ical time are reversed enabling it to provide the physical and chemical conditions desirable for optimal agricultural production. A rejuvenated soil would not exhibit the profile differentiation of a duplex soil. Geoderma Regional 7 (2016) 132–136 ⁎ Corresponding author at: Centre for Carbon, Water and Food, University of Sydney, Suite 103, Biomedical Building, 1 Central Ave, Eveleigh, New South Wales, Australia. E-mail address: damien.field@sydney.edu.au (D.J. Field). http://dx.doi.org/10.1016/j.geodrs.2016.02.001 2352-0094/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Geoderma Regional journal homepage: www.elsevier.com/locate/geodrs