Research being conducted at Wagga Wagga has indentified acid tolerance in new legume species that are due to become commercially available in the next two to three years.
The work being carried out by the Graham Centre (an alliance between NSW DPI and Charles Sturt University) has involved screening new cultivars and species of perennial forage legumes for tolerance to aluminium and manganese toxicities, which are common in low pH soils.
NSW DPI researcher, Brett McVittie, said there were currently no perennial legumes widely adapted to the high rainfall regions (600-800 mm) of southern Australia.
“Soils in this zone are typically too shallow and acidic for lucerne, and rainfall is too variable to reliably support white clover,” he said.
“There are several perennial legume species that have undergone development in recent years, which may be commercialised in Australia for use in these regions, including talish clover (Trifolium tumens), birdsfoot trefoil (Lotus corniculatus), Caucasion clover (T. ambiguum), tedera (Bituminaria bituminosa var. albomarginata) and tall verbine (Cullen australasicum).
“This study compared seedling tolerance of 23 perennial legume genotypes, as well as chicory, to aluminium and manganese stress, both of which commonly occur in acidic soils.”
McVittie said tolerance was assessed by observing seedling root and shoot growth after 23 days in hydroponic solution at five concentrations of aluminium and manganese, respectively.
“Results revealed that greater lotus (Lotus pedunculatus) was the most tolerant to aluminium and tedera was most tolerant to manganese toxicities,” he said.
“The native legume, tall verbine, was the least tolerant species to toxicities of aluminium, and lucerne was the least tolerant species to toxicities of manganese.
“Aluminium rankings for legumes from most tolerant to least based on the reduction of root length relative to the control solution is as follows: greater lotus, white clover, talish clover, birdsfoot trefoil, tedera, Caucasion clover, red clover, lucerne, strawberry clover and tall verbine.
“Manganese rankings using reduction in shoot weight relative to the control solution are in decreasing order: tedera, birdsfoot trefoil, caucasian clover, tall verbine, red clover, talish clover, strawberry clover, greater lotus, white clover and lucerne.”
Mr McVittie said acid soil tolerance was important, especially where high exchangeable aluminium was prevalent, as it stunts root growth which in turn limits access to soil water.
“This becomes a major problem during periodic droughts and it is often at this point that acid sensitive plants die,” he said.
“Previous research has demonstrated that increased acid soil tolerance can improve pasture establishment under dry seasonal conditions, presumably due to the increased capacity explore the soil volume for water.
“Acid soils can be ameliorated with lime. However, many soils remain acidic at depth, and the steep topography across the high rainfall zone typically limits the application and incorporation of lime.
”Mr McVittie said due to the variable nature of acidic soils, it has been demonstrated that acid tolerant species and cultivars should be used in combination with lime application.
“Legumes with improved acid tolerance should fix more nitrogen, subsequently increasing the nitrogen availability to companion grasses such as phalaris and cocksfoot,” he said.
“The will mean not only improved legume growth, but also improved grass growth and overall production of the pasture.”