Crop and Pasture Science
Volume 63 Numbers 8 & 9 2012
Pasture legumes are crucial to Australian agriculture, both as a nutritious feed for livestock and for their ability to add nitrogen to the soil. Australia has no native legumes suited to livestock grazing, but 47 species, particularly from the Mediterranean region, have been domesticated to cover a wide range of environments and farming systems. New pasture legume varieties have the potential to further increase productivity and sustainability of the livestock and grains industries.
The image of New Zealand is a green pastoral landscape with sheep and cows grazing ryegrass and white clover pastures. However, for much of the land east of the main mountains the summers are dry and pastures without irrigation stop growing during summer months. This paper outlines the current pasture research aimed at these dryland regions. The emphasis is on legumes that can fix nitrogen from the atmosphere, use water efficiently and provide high quality feed for animals.
Since the Roman Empire, lucerne (a.k.a. alfalfa) has been used as a major crop throughout global pastoral agriculture with research programs delivering new cultivars and management systems that solidified this traditional role. New roles include use as sprouts for salads, nutritional supplements, and bioenergy feedstock as well as the only forage crop commercially delivering biotech traits. Its future includes potential use in tropical or sub-tropical livestock production and to mitigate deficiencies in the widely used ryegrass-clover production systems.
Improving the genetic merit of temperate forage legumes helps ensure profitability and sustainability of Australasian pastoral industries. Increasing the rate of genetic gain using innovative breeding methods and new genetic resources is a key objective of white clover breeding in New Zealand. This paper reports on developments in Australasia in the areas of improving root systems for P uptake, pest tolerance, developing novel inter-specific hybrids and marker aided breeding. The successful trans-Tasman collaboration in white clover breeding is also discussed.
Nitrogen from biological fixation by pasture legumes currently supplies most of the protein in grain and animal products produced on Australian dryland farms. However, crop and pasture production is currently far below the water-limited potential. With achievable improvements in management the there can be sustainable nitrogen supply from biological fixation by pasture legumes for greatly increased grain and animal production.
CP12123Factors affecting the potential contributions of N2 fixation by legumes in Australian pasture systems
Biological nitrogen (N) fixation by pasture legumes has been calculated to contribute in excess of 3 million tonnes of N to Australian agriculture each year. While it has been demonstrated that many legume species have the potential to annually fix several hundred kg of N per ha, the actual levels achieved often fall far short of these level. The paper reviews the main biological and environmental variables that regulate N fixation as the principal source of renewable N to support pasture production and to maintain the organic fertility of agricultural soils.
Symbiotic nitrogen fixation by legumes is an important ecosystem process but has been down regulated by management in modern dairy systems which have favoured the use of nitrogen fertiliser and grass production over legumes. Multiple benefits are likely to accrue from encouraging legume growth but N fixation management requires careful attention to the needs of the symbiosis. This includes manipulating soil microorganisms and reducing urinary N returns from grazing animals, which would also provide multiple environmental benefits.
CP12154Nutrient surpluses in Australian grazing systems: management practices, policy approaches, and difficult choices to improve water quality
Adding nutrients to farm land can increase agricultural production, but many farm systems now have excess nutrient levels and can cause nutrient pollution of important waterways. Improved farm practices can reduce nutrient pollution but economic pressures for high production, generally resulting from greater fertiliser inputs, often conflict with this objective. Society will inevitably need to make varied and difficult choices to better balance production and environmental goals.
CP12190Exploring short-term ley legumes in subtropical grain systems: production, water-use, water-use efficiency and economics of tropical and temperate options
Pasture legumes can have several benefits in crop rotations including increasing soil fertility, managing soil diseases and weeds, but their perceived lower productivity and problems integrating them with crops have limited adoption. Several summer- and winter-growing forage legumes suitable for cropping systems tended to produce less biomass at lower water-use-efficiencies than annual forage grass alternatives. Despite this burgundy bean and lablab were consistently productive and profitable options that might provide alternative rotation options for farmers.
We’re going to make the plant researchers an offer they can’t refuse! We reduce the size of the research material by weeding and summarising its diversity. Can we? “Yes, we can!”. In this study, the diversity of a new pasture species is looked at, analysed and summarised while keeping most of the diversity within a minimum sample size. This is for the sake of efficient, inexpensive and speedy studies of this sample, very well-representing the natural diversity of a much larger group, in future.
CP12160Breeding and farming system opportunities for pasture legumes facing increasing climate variability in the south-west of Western Australia
The productivity of legume based pastures in the south-west of Western Australia is being impacted by climate change and an associated increase in climatic variability. A comprehensive understanding of the special attributes and adaptation of annual legumes when grown under Mediterranean climatic conditions is a precursor to designing specific strategies for adaptation to climate change. Based on such insights, we identify a combination of traits for targeted breeding and farming system opportunities to optimise the performance of legume pastures in variable and changing Mediterranean climates.
CP12173Breeding of an early-flowering and drought-tolerant Lotus corniculatus L. variety for the high-rainfall zone of southern Australia
For the first time, Lotus corniculatus has been bred for Australian Mediterranean climatic conditions. The new early flowering and drought tolerant cultivars will allow Australian farmers to utilize one of the most widely sown forage legumes in the world, now adapted to agricultural regions that are too dry for white clover or too wet or too acidic for lucerne.
Rhizobial inoculants applied to legumes have the potential to maximise crop productivity and increase nitrogen input in farming systems. The process of preinoculating seed with rhizobia usually includes additional agents which may be toxic and compromise survival of rhizobia. Our research has shown that rhizobial survival on seed is variable and affected by water quality, polymer adhesives, water activity on the seed coat, rhizobial strain and inoculant maturity, therefore each ingredient used in the preinoculation process should be examined for compatibility with rhizobial survival before use.
CP12130Development of an early season barrel medic (Medicago truncatula Gaertn.) with tolerance to sulfonylurea herbicide residues
In alkaline soils, sulfonylurea herbicides applied to crops can persist and adversely affect following barrel medic pastures. SARDI has developed barrel medics that grow well in the presence of sulfonylurea herbicide residues. A cultivar will be released soon that will allow farmers to grow productive barrel medic pastures in the year after a sulfonylurea herbicide application.
CP12138Spatial and temporal variation in soil Mn2+ concentrations and the impact of manganese toxicity on lucerne and subterranean clover seedlings
This study is a reminder of the damaging effects that Manganese toxicity can have on establishing legume pastures. It shows that manganese toxicity can lead to mortality of 35% of lucerne populations, can reduce root growth by nearly 40% and can even adversely affect relatively tolerant species such as subterranean clover. Manganese toxicity is best managed by combining soil amelioration with improved plant tolerance; however, this paper discusses the looming risk of developing ‘acid-tolerant’ cultivars without also addressing manganese toxicity.
Boron is present at toxic levels in the subsoils of much of the south-eastern Australian cereal-livestock zone where it can cause significant damage to pasture legumes including annual Medicago spp. The boron tolerance of newly developed annual medic cultivars was evaluated and presented in a table which summarises all known medic tolerance ratings from past and present research. This information will be useful for plant breeders, agronomists and farmers who manage soils with high boron levels.
CP12137A new biotype of bluegreen aphid (Acyrthosiphon kondoi Shinji) found in south-eastern Australia overcomes resistance in a broad range of pasture legumes
A new bluegreen aphid biotype (Acyrthosiphon kondoi Shinji) has been found in south-eastern Australia that causes severe damage and mortality in seedlings of previously resistant pasture legume cultivars. The new bluegreen aphid is confirmed to be widespread in south-eastern Australia.
CP12121Bean leafroll virus is widespread in subterranean clover (Trifolium subterraneum L.) seed crops and can be persistently transmitted by bluegreen aphid (Acyrthosiphon kondoi Shinji)
In the mid 2000s subterranean clover seed producers reported symptoms of a red-leaf disease associated with reduced seed yields. The present study found that Bean leafroll virus was widespread and persistently transmitted by bluegreen aphids. These results have implications for the management of Bean leafroll virus in seed crops, legume pastures and pulse crops and it is recommended that farmers adopt a management plan to minimise the risk of Bean leafroll virus to their legumes.
Lucerne can extend the growing season of winter-based pasture and respond quickly to rainfall after periods of drought, but is underutilised for livestock production in Australia. This paper investigates the opportunity to improve the adoption of lucerne; taking it from a specialty fodder crop that requires careful management to a robust traditional pasture. The plant traits and management principles that are important for achieving this vision are discussed.
This paper provides a summary of the Australian Legume Symposium and highlights the key research priorities that were identified by the participants. The organisation of pasture research and development in Australia was raised many times during the conference and emerged as a key concern. The views of participants were obtained through polling and included (amongst others): too much effort had gone into legume genotype development; resources should be guaranteed for maintenance research; mixed farmers faced a ‘nitrogen crisis’; and, that molecular techniques were unlikely to contribute to pasture cultivar development over the next decade.