A suite of novel pasture legumes and innovative establishment options has been under evaluation to give growers in low to medium-rainfall zones the ability to move more easily between pasture and crop sequences.
The Dryland Legume Pasture Systems (DLPS) project has been sourcing legume pasture species to decrease risk, increase profit and increase production system resilience for these regions.
Murdoch University led the pasture improvement program in WA, together with researchers from CSIRO and the Department of Primary Industries and Regional Development (DPIRD). The central and southern NSW component was led by the NSW Department of Primary Industries. Similarities in the agro-ecological regions has allowed much of the learning from the western node to be transferred and adapted to NSW.
These species have hard-seeded cultivars and produce their seed aerially. This means that they can be conventionally harvested and the seed grown on-farm at comparatively lower cost. This is a clear benefit when compared to the cost and complexity of harvesting subclovers that bury their seeds and medics that drop their pods.
Murdoch University and DPIRD have a history of developing robust pasture legume species, including bladder clover (Trifolium spumosum), biserrula (Biserrula pelecinus) and other annual clovers such as gland clover (Trifolium glanduliferum). They also developed the first cultivars of hard-seeded French serradella (Ornithopus sativus) and new cultivars of arrowleaf clover (Trifolium vesiculosum) and yellow serradella (O. compressus).
These pasture legumes all have unique breakdown patterns of their hard seed and germination, which is affected by local environmental conditions. These include the intensity of temperature variation and soil moisture over summer and autumn.
Identifying cultivars with appropriate hard-seed breakdown patterns for the target sowing environment is key to successful establishment and ongoing persistence in the rotation.
The most progressive hard-seeded breakdown feature is the suitability for sowing in late summer. The uniform dormancy release enables unprocessed seed (or pod segments in the case of serradella) to be sown in February or March, avoiding any clash with autumn cropping operations.
Once the seedbank has been established, hard-seeded pasture legumes can regenerate on demand between crops, meaning they will grow in subsequent years without needing to be resown.
This develops a nitrogen bank for subsequent crops and also gives growers the flexibility to move from crops to pastures to meet seasonal or market opportunities that arise. During the pasture phase, the legumes provide high-quality forage.
Matching to regional soil types and climatic conditions
Selecting hard-seeded pasture species that are widely adapted to climate and regional soil types and a range of farming systems is a challenge in a vast state such as WA. Traditionally, subclovers and medics have been used, but these species are falling behind in production and their suitability to evolving farming systems and changing climatic conditions.
However, hard-seeded varieties of species such as French serradella and biserrula have performed successfully on acid, coarse-textured soils in WA over several years. The serradella varieties Margurita and Fran2o , released in 2004 and 2020 respectively, have continued to be evaluated in the DLPS project.
With newly developed summer sowing practices, the new legume species have shown they can establish successfully on early autumn rains, producing more biomass, animal feed and nitrogen for following crops. They are also more competitive with weeds than current varieties.
The project has moved on to identifying new species that are adapted to WA’s alkaline, fine-textured soils. Trigonella (Trigonella balansae), bladder clover,a couple of medic species and Scorpiurus muricatus have been evaluated with grower groups at Esperance, Mingenew and Narembeen.
In contrast, the temperate environment of central and southern NSW usually receives more summer rainfall than most parts of WA. The higher clay content and good soil moisture retention of the regional soils generally mean faster seed breakdown and more opportunities for summer sowing across a wider range of legume species.
Additional species successfully established by summer sowing in NSW include arrowleaf clover, biserrula and gland clover. Trigonella has also performed well on acidic soils (pHCa 4.8 to 5.2) in NSW, indicating it may be a useful species across a range of soil conditions.
The hard-seeded legumes have shown tremendous adaptation to variable climatic conditions, partly attributed to root systems that significantly extend past the average depth of the older medic cultivars.
In NSW, under severe drought conditions in 2019 where some sites received less than 70mm growing season rainfall, hard-seeded legumes such as biserrula set sufficient seed (>150 kg/ha) for ongoing regeneration. However, subterranean clover and annual medics died before producing seed. Under the wetter-than-average seasons of 2020 and 2021, summer sown hard-seeded legumes produced four to 10 times more herbage than conventionally sown traditional legumes.
In commercial settings, hard-seeded legumes established in the drought of 2017–19 have regenerated strongly following the break of the drought and traditional legumes have had to be resown.
Leading species or accessions for probable release and suitable for use in summer sowing include bladder clover (acc. CYP43.6.1) and trigonella (acc. APG5045 early). Additionally, the recent French serradella release (cv. Fran2o) from the WA node of the project showed consistent performance on acid soils in NSW and WA.
Arrowleaf clover (cv. Cefalu) continues to perform well in summer sowing situations in NSW, while the addition of a proportion of scarified seed of biserrula (cv. Casbah) to unprocessed seed has resulted in greater early vigour of summer sown stands in NSW.
Care with pairing rhizobia
Certain pasture legumes such as French serradella are obligate nitrogen-fixing plants, which means they fix nitrogen much more efficiently than plants such as medics even when soil nitrogen levels are high.
Rhizobia need to be carefully matched to legume species and soil type. Pictured here is the French serradella Fran2o, which was inoculated with Group G/S rhizobia. Photo: Paul Sinderberry, Condobolin
It is vital that hard-seeded pasture species are matched with the appropriate rhizobia species to optimise production and increase soil nitrogen reserves for subsequent crops. Hard-seeded annual clovers require Group C inoculant, French serradella requires Group G/S, and biserrula requires the Biserrula Special inoculant.
Nearly all of the nitrogen-fixing strains of rhizobia are introduced to Australia from the Mediterranean region. Working with the Centre for Rhizobium Studies based at Murdoch University and supported by GRDC, the team has access to the world’s largest rhizobia genebank to match appropriate elite nitrogen-fixing species and strains to the hard-seeded pasture legume species.
Rhizobiologists and geneticists identify stable rhizobia populations that fix nitrogen efficiently, are tolerant to desiccation and hostile soil conditions, and are suited to the inoculant manufacturing process.
The correct matching of rhizobial strain with the legume host ensures efficient nitrogen fixation for increased pasture production and benefits to following crops. Improvements in rhizobial inoculant can benefit current and new legume species. For instance, research is underway to find a better match for Scorpiurus muricatus, with germplasm from Morocco and Greece being assessed for both the legume and rhizobia.
This research was part of the national Dryland Legume Pasture Systems project supported by the Australian Government Department of Agriculture, Water and Environment (DAWE) Rural R&D for Profit program and the Grains Research & Development Corporation, Meat & Livestock Australia and Australian Wool Innovation.
More information: Robert Harrison, robert.harrison@csiro.au; Belinda Hackney, belinda.hackney@dpi.nsw.gov.au; Ron Yates, ronald.yates@dpird.wa.gov.au