Mike Ewing

The potential for developing fodder plants for the salt-affected areas of southern and eastern Australia: an overview

This paper reviews the major issues that impact upon the development of improved fodder species for saline environments across temperate Australia. It describes past and present research that has been, or is being, undertaken towards improvements in salt tolerance in forage species within Australia in relation to the principal regions where salinity occurs. It includes a discussion on the mechanisms of salt tolerance in plants. An extensive list of known or potential salt-tolerant fodder species is provided and the key opportunities for advancement within each of the 4 major forage groups: grasses, legumes, herbs and shrubs are discussed. Constraints to developing new salt and waterlogging tolerant fodder species are identified. A number of recommendations are made for research that should ensure that Australian producers have access to a new array of productive fodder species suited to saline environments.

The search for new pasture plants to achieve more sustainable production systems in southern Australia

Increasing the proportion of the landscape planted to deep-rooted perennial pasture species is recognised as one of several remedial actions required for the control of dryland salinity in southern Australia. The widespread use of perennials in farming systems is limited at present by the lack of well-adapted perennials that can be grown to reduce recharge in a landscape where drought, soil acidity, temporary waterlogging, infertile soils and unrestricted grazing prohibit the use of many species. The range of plants adapted to salinity also needs to be expanded to stabilise and ameliorate soils already degraded by rising watertables and to increase the profitability of grazing discharge regions within the landscape. This paper describes the steps involved in a national forage screening and breeding program initiated by the Cooperative Research Centre (CRC) for Plant-based Management of Dryland Salinity1, seeking to expand the range of perennial and or salt-tolerant forage plants that can be incorporated into farming systems of southern Australia. It describes the target environments, soil constraints, farming systems and the criteria being considered when assessing the potential of new plants, including assessment of the weed risk posed by introducing new species. This paper forms an introduction to a special issue which presents the outcomes of the pasture species field evaluation and plant breeding program conducted by the CRC.

A mathematical programming model of a crop-livestock farm system

Abstract A whole-farm mathematical programming model has been built for dryland crop-livestock farms in Western Australia. The multidisciplinary approach used for model building is presented and the resulting model structure is described. It is a mixed integer programming model which represents, in some detail, the biological, technological and financial relationships of the farming system and stresses the interdependencies of enterprises. The model is used to investigate the extent to which positive interactions between different enterprises influence the optimal farm plan. The management issue considered is the division of land between crop and pasture production. It is concluded that, for the farming system considered, interactions do have an influence on profit and the optimal farm plan.

Perennial wheat: a review of environmental and agronomic prospects for development in Australia

Perennial wheat could improve grain production systems in Australia by rectifying many environmental problems such as hydrological imbalance, nutrient losses, soil erosion, and declining soil carbon and soil health. There are also potential direct production benefits from reduced external inputs, providing extra grazing for livestock in mixed farming systems, as well as benefits for whole-farm management which may offset lower grain yields. In addition to universal issues of domestication and breeding of perennial wheat, specific challenges for perennial wheat in Australias dryland systems will include tolerance of water deficit and poor soil environments, and the risks of hosting foliar pathogens over summer. Temperate perennial forage grasses could indicate the potential distribution and traits required in perennial wheat adapted to more arid environments (e.g. summer dormancy). Several Australian native and exotic perennial relatives of wheat could also provide sources of disease resistance, and tolerance of soil acidity, drought, salinity and waterlogging. Still, several farming systems could accommodate perennial wheat with inconsistent persistence in some environments. While developing perennial wheat will be challenging, there is significant opportunity in Australia for perennial wheat to diversify current cropping options. The risks may be minimised by staged investment and interim products with some immediate applications could be produced along the way.

Tolerance of aluminium toxicity in annual Medicago species and lucerne

A rapid (7 day) solution-based screening test was developed using 15 annual Medicago cultivars and one M. sativa. Based on a relative root regrowth after exposures to aluminium (Al), Zodiac (M. murex), Orion (M. sphaerocarpos) and the M. polymorha cultivars Santiago, Cavalier and Serena had the greatest Al tolerance. Herald (M. littoralis) and Rivoli (M. tornata) were most sensitive. Ranking for Al tolerance from the solution culture correlated well (r = 0.80) with ranking for tolerance of the 16 genotypes grown in an acidic soil (unlimed pHCa 4.1). We screened 17 Australian populations of lucerne (M. sativa) using a 24 h ‘pulse’ of 75 µmol/L Al, and a three day ‘recovery’ of 10 µmol/L Al. We identified and recovered plants with a root regrowth of ≥5 mm in all 17 populations with selection intensities of 2 to 4%. Four of these selected populations (Aurora, UQL-1, A513 and TO2-011) were polycrossed within each population to produce four populations of seed from the cycle 1 selections. The length of root regrowth under Al stress was improved for all four populations of cycle 1 selection (P ≤ 0.001; from 2.6 mm for the original populations to 6.3 mm for the cycle 1 selections). In a subsequent experiment the cycle 2 selections from Aurora, UQL-1 and TO2-011 had significantly greater root regrowth than both the cycle 1 selections (P ≤ 0.001; 8.3 cf. 6.6 mm) and the unselected populations (3.0 mm). The selections from TO2-011 appeared to have greater improvement in the average length of root regrowth after 2 cycles of selection. Selected germplasm was more tolerant than GAAT in our evaluation. Based on estimation of realised heritability, it seemed likely that higher selection intensities would give more rapid improvements in tolerance. Our studies have not investigated the physiological basis of any tolerance of Al which we observed.

Annual Pasture Legumes: A Vital Component Stabilizing and Rehabilitating Low-Rainfall Mediterranean Ecosystems

Surveys of the distribution of annual legumes in low - rainfall Mediterranean areas show them to be a persistent element of ecosystems that exhibit great climatic and edaphic diversity and are present even when these systems have been substantially degraded by long - term human disturbance. Studies of the productivity of degraded grasslands in low - rainfall Mediterranean environments indicate that productivity is usually in the range of 2-5 kg mm-1 mean annual rainfall, i.e., well short of potential. It can be enhanced by a range of interventions that favor annual legumes. Effective strategies include control of grazing (both intensity and timing), input of exogenous nutrients, particularly phosphorus, and the addition of legume seed, or a combination of all of these. Recent studies have greatly increased understanding of the mechanisms leading to resilience of annual legume populations. This knowledge is useful in designing rehabilitation programs. It has become clear that the combination of a high leve...

Preference of sheep among annual legumes is more closely related to plant nutritive characteristics as plants mature.

We hypothesised that the preference of sheep among a wide range of annual legumes at successive stages of plant phenology would be related to laboratory measurements of the chemical composition of the forage. We tested this by examining the relative preferences of sheep among 20 genotypes of annual plants at three phenological stages of plant growth usingtheChesson-Manlyselectionindex.Plantmaterialwascollected forlaboratoryanalysesateachphenological stage and samples were analysed for nitrogen, sulfur, neutral detergent fibre, acid detergent fibre, in vitro digestibility and water soluble carbohydrates. Sheep differed in relative preference among the plant genotypes within and between each of the three phenological stages. Vegetative characteristics that were correlated with relative preference also differed with plant phenology. Measured characteristics of the plant material explained an increasing proportion of the variance in relative preference with successive phenological stages (4.8, 51.1 and 60.9% at the vegetative, reproductive and senesced stages; P < 0.001). The relative preference of the sheep depended on the overall quality of the vegetation. When the quality of the vegetation was high, relative preference did not correlate well with measured nutritive characteristics. However, whenthevegetationwasoflowquality,sheepselectedplantswithcharacteristicsassociatedwithhighernutritivevalue.We conclude that sheep adopt different foraging strategies in response to changing vegetation characteristics and increase their preference for plants that increase their intake of digestible dry matter as the sward matures.

Comparative water use by Dorycnium hirsutum-, lucerne-, and annual-based pastures in the Western Australian wheatbelt

Dryland salinity in southern Australia has been caused by inadequate water use by annual crops and pastures. The purpose of this study was to compare the water use of annual pastures and Medicago sativa L. (lucerne) with Dorycnium hirsutum (L.) Ser., a potential new perennial forage species. The soil water dynamics under bare ground, annual legume-, lucerne-, and D. hirsutum-based pastures were compared at 2 sites in the low- (Merredin) and medium- (New Norcia) rainfall wheatbelt of Western Australia between September 2002 and February 2005. Soil under D. hirsutum was drier than under annual pastures by 8–23 mm in Year 1, 43–57 mm in Year 2, and 81 mm in Year 3. Lucerne used little additional water (<19 mm, n.s.) compared with D. hirsutum and profile soil water content was similar under both species throughout the experiment. At Merredin, annual pastures used water to a depth of 1.0 m, whereas under both D. hirsutum and lucerne in the first 3 years after establishment the successive maximum depth of water use was 1.0, 1.8, and 2.2 m. At New Norcia, additional soil water was extracted by lucerne and D. hirsutum at depths <1.0 m and no difference between treatments was detected below 1.0 m. Biomass of D. hirsutum pasture harvested in autumn contained minimal annual components and was 15–50% of that produced by lucerne- or annual legume-based pastures. D. hirsutum and lucerne plant density declined each summer (25–80%), but D. hirsutum density was lower than lucerne due to poorer establishment. Nonetheless, the comparable water use of lucerne and D. hirsutum suggests that D. hirsutum could make reductions in recharge similar to those of lucerne in the Western Australian wheatbelt.

Increased yield in annual species of Medicago grown in acidic soil in response to inoculation with acid tolerant Rhizobium meliloti

Poor nodulation of annual species of Medicago in acid soils has historically limited the commercial exploitation of this genus to soils with pH above 6 (1:5, 0.01 M CaCl2). The objective of this research programme was to improve the level of acid tolerance in both the host and microsymbiont, so that reliable nodulation could be achieved in self-regenerating annual pastures grown in rotation with cereals on soils in the pH range 4.5–5.0. The results reported describe the method of selection and production benefits gained from inoculating annual medics (M. polymorpha, M. murex) with strains of Rhizobium meliloti selected for saprophytic competence in acid soils. Strains of Rhizobium meliloti collected from acid soils in Sardinia were screened in 7 years of experimentation for their ability to colonise and persist in acid soils (pH 4.6–5.0) in the semi-arid region of Western Australia. Several of the most successful strains were then used in a small plot trial to assess their impact on herbage and seed production in regenerating annual pastures. These production parameters were highly correlated with rhizobial persistence and nodulation in an acid soil. Inoculation with the most acid tolerant strain increased herbage production by 51%, and increased seed yield by 31%.

Breeding and farming system opportunities for pasture legumes facing increasing climate variability in the south-west of Western Australia

Abstract. The south-west of Western Australia has experienced a declining trend in annual rainfall and gradual warming over the last 30 years. The distribution of rainfall has also changed, with lower autumn rainfall, patchy breaks to the season, and shorter springs. This has important implications for the productivity of legume pastures in the region, which is dominated by annual species, particularly subterranean clover (Trifolium subterraneum L.), annual medics (Medicago spp.), serradella (Ornithopus spp.), and biserrula (Biserrula pelecinus L.). For annual pasture legumes, appropriate patterns of seed softening and germination behaviour, efficiency of phosphorus and potassium uptake, responses to elevated levels of atmospheric CO2, and drought resistance of seedlings and mature plants will assume increasing importance. While these traits can be targeted in pasture breeding programs, it will also be important to exploit farming system opportunities to optimise the annual legume component of the feed base. These opportunities may take the form of incorporating strategic shrub reserves and grazing crops to allow for pasture deferment in autumn–winter. Perennial forages may become more important in this context, as discussed in terms of the development of the perennial legume tedera (Bituminaria bituminosa var. albomarginata C.H. Stirton).