Management of soil acidity in long-term pastures of south-eastern Australia: a review

Abstract

Acidification of non arable soils under long-term pasture presents a major agricultural problem in the high rainfall areas (≥600 mm/year) of central and southern New South Wales and north-eastern Victoria. Some of these soils were already strongly acid to depth before agriculture. Evidence suggests that persistence of pasture species tolerant of acidic soils is being affected adversely on a number of severely acidic soils. Acidification processes are well understood but the capacity for grazing enterprises to pay for amendment by lime application is a major constraint in long-term pasture areas. In addition, soil acidification is likely to have substantial off-site effects on water quantity and quality and as a result, on dryland salinity. However, there is a paucity of scientific evidence to link soil acidity and dryland salinity in this way. Production from a grazing enterprise can be maintained by selecting plants for tolerance of acidity, surface application of lime or a combination of both. Responses by subterranean clover, lucerne and perennial grass (mainly phalaris and cocksfoot)-based pastures to incorporated lime are reported, but there is limited evidence of responses to surface applied lime. The movement of the lime effect into the soil from surface application is suggested as a major factor in controlling lime responses by plants. There is a need for more confidence in the benefits of topdressed lime in non arable soils before producers are likely to adopt the practice. High subsurface acidity in many soils is a major limitation to the range of species that can be grown. In the longer term, the use of lime may remove constraints on the use of productive species such as lucerne. Other options for acidic soils where slope is less than 10% are for the grazing system to be modified or intensified, or for crop or horticultural production. Costs of lime could be justified through more profitable enterprises than traditional grazing operations. Low input systems based on native grasses are intrinsically appealing, however, this is only possible where a premium is paid for such produce (such as super fine wool). Forestry is an option where suitable land and infrastructure are present and should slow soil acidification and minimise off-site impacts. Land retirement may be a useful option for some parts of the landscape that contribute disproportionately to environmental problems. Private and government funded land retirement may have a role to play.

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

“…Helyar 1991;Scott et al 2000) and waterlogging (e.g. Belford et al 1990;McFarlane 1990, 1995;MacEwan et al 1992;Sarlistyaningsih et al 1995;Christy 1996;Malik et al 2002;Barrett-Lennard 2003;Peries et al 2004) on soil processes and plant growth responses.…”

“…Surface acidity in the A1 horizon is already a management issue for HRZ producers, particularly on texture-contrast soils (Helyar 1991;Coventry 1992;Scott et al 2000). This has resulted from elevated rainfall, more intensive crop production strategies (e.g.…”

“…This has resulted from elevated rainfall, more intensive crop production strategies (e.g. increased application of N), an environment more conducive to nutrient turnover and N mineralisation, and the greater opportunity for losses of excess nutrients through leaching (Helyar 1991;Raij 1991;Coventry 1992;Scott et al 2000). Current data (NLWRA 2005) suggest that subsoil acidity in the HRZ is generally at a level that will not inhibit the production of most crop species.…”

“…Current data (NLWRA 2005) suggest that subsoil acidity in the HRZ is generally at a level that will not inhibit the production of most crop species. However, the development of subsoil acidity is a hidden but significant threat as cropping activities expand in the HRZ and increases in nitrogen fertiliser application occur in order to meet higher yield expectations (Helyar 1991;Coventry 1992;Scott et al 2000). Subsoil acidity in the Southern Highlands and Tasmanian HRAEZs may require further investigation to determine whether it is actually a problem on arable land.…”

“…Acid surface soils can be readily modified by incorporation of lime, but amelioration of low pH in the subsoil is more challenging (Scott et al 2000). Surface applications of lime can, with sufficient time, ameliorate acid subsoils.…”