Crop production in the high rainfall zones of southern Australia — potential, constraints and opportunities

Abstract

Annual cropping has been expanding in the high rainfall zone of southern Australia. The higher rainfall and longer growing season compared with the traditional wheatbelt contribute to a much higher yield potential for major crops. Potential yields range from 5 to 8 t/ha for wheat and 3 to 5 t/ha for canola, although current crop yields are only about 50% of those potentials. The large yield gap between current and potential yields suggests that there is an opportunity to lift current yields. Both genetic constraints and subsoil constraints such as waterlogging, soil acidity, sodicity, and high soil strength contribute to the low yields. Waterlogging is a widespread hidden constraint to crop production in the region. Controlling waterlogging using a combination of raised beds and surface or subsurface drains is the first step to raise the productivity of the land. Increasing root growth into the subsoil remains a key to accessing more water and nutrients for high yield through early planting, deep ripping, liming and use of primer crops to ameliorate the subsoil. In order to realise the high yield potential, it is essential to achieve higher optimum dry matter at anthesis and high ear number through agronomic management, including early sowing with appropriate cultivars, a high seeding rate and application of adequate nitrogen along with other nutrients. Current cultivars of spring wheat may not fully utilise the available growing season and may have genetic limitations in sink capacity that constrain potential yield. Breeding or identification of long-season milling wheat cultivars that can fully utilise the longer growing season and with the ability to tolerate waterlogging and subsoil acidity, and with disease resistance, will give additional benefits. It is concluded that improving crop production in the high rainfall zone of southern Australia will require attention to overcoming soil constraints, particularly waterlogging, and the development of longer-season cultivars.

Dual-purpose cropping – capitalising on potential grain crop grazing to enhance mixed-farming profitability

“…An obvious first target was the estimated 6M ha of arable land in other high rainfall zones of Australia (Zhang et al 2006), where livestock enterprises comprise a significant portion of the farm enterprise, and where cropping has recently expanded (Riffkin et al 2012). Significant areas of the south-eastern and north-eastern Tablelands and slopes, and the southern and western high rainfall zones have suitable soils and climates for cropping, well suited to longer-season cereal and canola varieties, and predominately mixed farming enterprises that could capitalise on dual-purpose crops.…”

Why non-native grasses pose a critical emerging threat to biodiversity conservation, habitat connectivity and agricultural production in multifunctional rural landscapes

“…In rough, sloping or infertile areas normally considered unsuitable for cropping, such practices can also drive further ecosystem degradation via erosion, soil compaction, and loss of organic matter. The fact that this process has received little attention is surprising given that the conversion of grazing lands to more intensive pasture or cropping regimes on similar scales in response to other drivers (e.g., Zhang et al 2006) is a serious contemporary threat to biodiversity conservation in Australian rangelands and native pastures. The use of fire as a management tool to maximise the palatability of undesirable species (e.g., H. hirta and E. curvula) also clearly has the potential to accelerate broad scale biodiversity loss in Australian rangelands and pastures, especially where the removal of NNG infestations is economically or biologically impossible (e.g., Lodge et al 1994), and where native species have low tolerance to changing fire regimes.…”

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

“…This amount would represent a capacity to more than double current gross national production of grains in Australia. APSIM modelling by Zhang et al (2006) predicts yields of 3-5 t/ha for canola and 5-8 t/ha for wheat if all constraints are removed. …”

“…For Western Australia, Poole et al (2002) refer to 400-700 mm annual rainfall areas, while Zhang et al (2006) recognise 450-800 mm annual rainfall as the HRZ with rainfall exceeding one-third of evaporation for 7 months of the year. An earlier definition of the HRZ used by the GRDC follows that of Prescott and Thomas (1949), who defined the lower climatic limit of the high rainfall cropping areas as 'the areas where rainfall exceeds one third of evaporation for 9 months of the year or more'.…”

“…Potential for crop production in the HRZ is high. Zhang et al (2006) reviewed the potential for annual cropping in the HRZ of southern Australia, concluding that current crop yields are only 50% of potential and that the major constraints are waterlogging, lack of adapted cultivars, limited root penetration due to poor soil structure and acidity, and poor nutrient supply.…”