Salinity is a widespread problem caused by an imbalance between rainfall and
transpiration in the dryland cropping systems of southern Australia. The need
to use more perennials has been identified and this paper examines the
possibility of replacing annual with perennial pasture legumes and the
germplasm available to do so. While lucerne is already used widely in eastern
Australia it has only recently been adopted in the wheat belt of Western
Australia. There are doubts about its adaptation to acid soils and to climates
where summer rainfall is low and ambient temperatures are high. There is also
a need to diversify the species available to reduce the likelihood of invasion
by exotic diseases and insects.
Several genera are likely to be of value in this respect, although few will be
as widely adapted as lucerne. Perennial legumes are found in environments
ranging from alpine to desert. Targeted collections of genera from the dry
areas, especially where soils are acid, are likely to yield species of value.
These may include perennial species of Astragalus,
Hedysarum, Lotus,
Onobrychis, Psoralea, and
Trifolium. Some Australian genera, for example
Swainsona, Glycine, and
Cullen may also be of value. Most of these genera are
from alkaline soils, and the need to cope with acid soils that are often high
in free aluminium is seen to limit their use in southern Australia. However,
since virtually nothing is known of the ecology and ecophysiology of species
from the dry areas, it is possible that through selection and the use of
adapted rhizobia, some at least may be of value in Australian conditions.
Cropping in rotation with perennial legumes is likely to involve several
changes in farming systems. It is impossible to predict their nature but it is
essential that we understand what these changes are before the species are
widely introduced. Account must also be taken of their ability to use water.
It is entirely possible that perennials from dry areas are dormant in summer
despite the fact that there is no evidence in the literature to this effect.
It was concluded that although lucerne is suitable for phase farming,
alternatives to lucerne are needed. They will have to match the water-using
and nitrogen-fixing capacities of lucerne, and farming systems will be
required that make full use of the new germplasm. Collaboration with
institutions in the Mediterranean basin and elsewhere is needed and a
beginning has been made in this direction.
Nitrogen fertility in semiarid dryland wheat production is challenging for beginning organic farmers