Ecology of herbaceous perennial legumes: a review of characteristics that may provide management options for the control of salinity and waterloggingin dryland cropping systems

Salinity is a widespread problem caused by an imbalance between rainfall an d 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 ger mplasm 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 Au stralia. There are doubts about its adaptation to acid soils and to climate s 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 environmen ts ranging from alpine to desert. Targeted collections of genera from the d ry areas, especially where soils are acid, are likely to yield species of v alue. These may include perennial species of Astragalus, Hedysarum, Lotus, Onobrychis, Psoralea, and Trifolium. Some Australian genera, for example Sw ainsona, 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 h igh in free aluminium is seen to limit their use in southern Australia. How ever, since virtually nothing is known of the ecology and ecophysiology of species from the dry areas, it is possible that through selection and the u se of adapted rhizobia, some at least may be of value in Australian conditi ons. Cropping in rotation with perennial legumes is likely to involve several ch anges in farming systems. It is impossible to predict their nature but it i s essential that we understand what these changes are before the species ar e widely introduced. Account must also be taken of their ability to use wat er. It is entirely possible that perennials from dry areas are dormant in s ummer 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, alter natives 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 i n the Mediterranean basin and elsewhere is needed and a beginning has been made in this direction.