New Legume Species as Opportunistic Summer Crops for Southern Australia

By BCG Staff and Contributors
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By Audrey Delahunty, Ash Wallace, Sally Norton, Penny Riffkin, Brendan Christy, Jason Brand, Frank Henry, Eileen Perry, Alex Clancy, Garry O’Leary, Cassandra Walker, Joshua Fanning, Sachesh Silwal, Debra Partington and James Nuttall (Agriculture Victoria)

 Take Home Messages

  • Commercial cultivars of mungbean, soybean and lab lab (as fodder) have potential as opportunistic crops in Victoria where summer rainfall is significant.
  • Suitability of summer legumes was best in high rainfall regions (eg. south west and north east Victoria), with north eastern Victoria being most suitable for supporting immediate adoption of commercially available summer legumes.
  • Breeding for better adapted varieties and further research into agronomic management is needed to enable incorporation of summer legume crops into Victorian cropping systems.

Background

Legume crops constitute 10 per cent of grain production across south east Australia, which is mostly winter sown. This includes lentil, chickpea, field pea and faba bean. Expansion into summer crop options may allow growers to capture greater value from the farming system by using summer rainfall. The addition of sub-tropical legume species as summer crops, has the potential to provide a diversified income stream as grain and/or fodder, as well as enhancing soil nutrition through additional nitrogen fixation and using out-of-season rainfall. Additionally, summer crops within the high rainfall zones may boost production of subsequent winter crops through dewatering of the soil profile and limiting potential impacts of waterlogging.

This paper reports on a series of experiments evaluating the suitability of summer legume crops typically grown in central and southern Queensland and northern New South Wales. These crops include adzuki bean, mungbean, cowpea, pigeon pea, lab lab and soybean, which are grown under both dryland and irrigated conditions in these environments. This work particularly focused on crop development (timing of flowering, podding and harvest), water requirement and temperature adaptability across a range of agroecological zones within Victoria. 

Aim

This research project was established to assess the suitability of a range of alternative legume species, as an opportunistic summer crop, to cropping regions in southern Australia.

Paddock Details

Locations: Ouyen, Woomelang, Horsham, Hamilton and Rutherglen

Crop year rainfall: See Table 1

GSR (Oct–Apr): See Table 1

Soil type: Mallee – Calcarosols, Wimmera – Vertosols,
Hamilton and Rutherglen – Chromosols

Paddock history: Predominantly long fallow

Trial Details

Crop type/s: Adzuki bean, mungbean, cowpea, pigeon pea, lab lab, soybean

Treatments: Species and varieties, time of sowing (TOS), environment

Target plant density: Adzuki bean, mungbean, dry bean: 35 plants/m²
Cowpea: 25 plants/m²
Lab lab: 12 plants/m²
Soybean, pigeon pea: 40 plants/m²

Seeding equipment: Tyne seeder with narrow point press wheels, 25 to 36cm row spacing

Sowing date: Sowing window September to December (see Table 1) Replicates: Three

Harvest date: March to June

Trial Inputs

Fertiliser: Mono-Ammonium Phosphate as per standard rate for each region (50 to 80kg/ha at sowing)

Herbicide: Pre-emergent only: Round-up (2L/ha) and Treflan (1L/ha)

Insecticide: Trial managed as per best practice

Fungicide: Trial managed as per best practice

Seed treatment/inoculant: Gaucho and species-specific rhizobia applied to seed before sowing

Irrigation: A small amount of supplementary irrigation was applied before sowing, and afterwards at some sites, to establish the summer crops over the three-year experimental period so the yield potential could be realistically assessed.

Method

The experimental program was conducted over three consecutive summer seasons (2019/20 to 2021/22) and evaluated the viability of a broad range of alternative legume species within Victoria. The species were adzuki bean, cowpea, lab lab, mungbean, pigeon pea, navy bean, and soybean. At each location, crop response across species and variety combination were compared for different times of sowing. Trials were a complete randomised block design replicated three times. Supplemental irrigation equivalent to 20mm at sowing was applied to simulate a break opportunity. In the drier environments follow-up water was scheduled at key times to alleviate terminal water stress and provide a realistic yield potential (Table 1).

Production potential (yield and biomass), critical response to temperature (ambient and soil), water availability, latitude and phenology were assessed to inform the adaptability of each species across a range of environments.

Results & Interpretation

Fodder and grain yield potential of summer legumes

For the higher rainfall regions of Victoria, soybean and pigeon pea produced the highest average biomass in north-eastern Victoria. In south west Victoria, soybean and mungbean produced the highest biomass (Figure 1). For these regions, crops were grown under largely rainfed conditions (Table 1). While the supplementary irrigation allowed all crops to establish, it did not significantly advantage those growing in the drier areas and the potential yield assessments are considered realistic. In the Wimmera, highest biomass was observed for lab lab and pigeon pea. In the Mallee, lab lab produced the highest biomass, while cowpea, mungbean and pigeon pea all had equivalent biomass. Soybean growth was poor. Overall, biomass production at harvest typically ranged from 1t/ha in the Mallee to 2–3t/ha in the Wimmera, 2–5t/ha in south west Victoria and 4t/ha or more in north east Victoria across all species. 

For north east Victoria, soybean with median yields of 3.121t/ha and mungbean (1.075t/ha) were the highest yielding of the species. Pigeon pea was the lowest yielding (Figure 2). For south west Victoria, soybean was also high yielding, with median yield of 1.856t/ha. Mungbean (0.82t/ha) and navy bean (1.183t/ha) also yielded moderately well. Despite cowpea producing modest biomass in this environment, it did not translate to yield, which is likely related to limited flowering and seed set. In the Wimmera, median yield of all species was less than 1t/ha. The highest yielding species were soybean (0.701t/ha) and mungbean (0.542t/ha). In the Mallee, mungbean was the highest yielding species (0.453t/ha) and soybean and pigeon pea did not yield. Overall, the trend of summer legume yields across environments was Mallee < Wimmera < south west < north east.

Suitability of commercial summer legumes to environments and farming systems In southern Australia, harvest of winter crops generally begins as early as late October or as late as January. The window for ‘double-cropping’ would be limited in many environments unless sowing of summer crops was delayed until January. For testing the summer legume species, experiments were established based on an assumption that the summer legume would follow either a winter fallow or a hay/silage crop. It was determined that the optimal rate of emergence (< 12 days) occurred for summer legumes at soil temperatures of at least 15°C with limited differences between species. Despite differences in the rate of establishment, there was no relationship between soil temperature and final establishment, except where soil temperatures at the time of sowing were very low ie. less than 12°C).

Growing season length of summer crops has significant implications for their suitability within continuous winter cropping enterprises. Mungbean was the fastest maturing species, while pigeon pea was the slowest, often failing to mature before sowing of a subsequent winter crop (Figure 3). Soybean was also slow to mature, often reaching flowering in relatively short timeframes, but having a protracted pod-filling period and being slow to desiccate due to cool conditions occurring in early autumn. Balancing the combination of sowing and harvest dates, mungbean are best suited across a range of environments and pigeon peathe least suited. With appropriate management and germplasm improvement, soybean and cowpea have the potential to fit the 1 October to 20 April window. Cowpea may be best as a fodder option.

Commercial Practice and On Farm Profitability

In addition to regionally-specific data observed through the experimental program, the long-term production potential of summer legumes in south east Australia was assessed with biophysical modelling. This included mapping long-term simulated yield of soybean and mungbean to identify zones most suited to their production. There is a trend of higher yield potential in the high rainfall regions of north east and south west Victoria for soybean (Figure 4). In these regions, average soybean yield was 1–1.5t/ha when a November sowing opportunity occurred (about 70 per cent of years) and stored soil water at sowing was at 80 per cent of plant available water (PAW). In contrast, for low rainfall regions such as the Mallee, expected average yields were 0.5–0.75t/ha where sowing opportunities occurred (about 60 per cent of years). Under conditions of lower stored soil water, expected yields decreased in a spatial pattern broadly following rainfall gradients in a south east direction. Experimentally, we also determined that summer crops grown in drier environments caused a yield penalty to the following winter crop. For every tonne of summer legume biomass there was a wheat yield penalty of 0.4–0.5t/ha

Long-term modelling of yield potential across Victoria suggests:

High rainfall zone: Suited to opportunistic cropping of summer legumes as grain or fodder. The most promising options include soybean, mungbean and lab lab (fodder).

Low and medium rainfall zones: A summer legume phase was determined to be high risk. Species such as lab lab or mungbean grown for fodder were the most appropriate in years with significant spring rainfall.

Considerations for Growing a Summer Legume

  • Water supply: A wet soil profile and/or forecast indicating significant spring/summer rainfall (>150mm) are important to support growth of a summer crop. Sowing should also be timed with a rainfall event (25mm) and suitable soil temperature. The risk profile based on climate is region specific and should be considered.
  • Labour availability: Incorporating a summer crop has implications for winter crop operations such as time of sowing relative to hay production and time of harvest relative to sowing of the subsequent winter crop.
  • Land availability: Sowing between October and December relies on either a winter fallow, winter crop failure (eg. waterlogged) or winter crop removal for hay or silage. Opportunity to sow a summer legume after harvesting a winter crop may occur, but this would mean sowing into the driest time of year for most environments.
  • Risk management: Dual purpose (fodder and grain) species are an important risk management strategy, and this is particularly relevant if considering opportunistic sowing of summer legumes in dryland systems in Victoria.
  • Crop and variety selection: For dual purpose options, mungbean and soybean are the best adapted to Victorian growing conditions. Mungbean has a shorter growing season that is compatible with a double-cropping rotation. Lab lab is a suitable fodder crop option, producing high biomass and the capacity to increase soil N.
  • Agronomy and advice: Given the novel nature of growing summer legumes in Victoria, localised advice is limited. Agriculture Victoria can assist with establishing networks for procuring seed and linking with existing organisations, such as the Australian Mungbean Association and Soy Australia. Further research is needed to identify optimal management of these new species under Victorian conditions.
  • End user and Market access: Since summer legume production in Victoria is currently limited, it is likely grain will need to be delivered long distances (compared with traditional winter crops) and marketing options developed over time. However, there are processors seeking certain species in Victoria if the supply chain were to develop.

Acknowledgements

The ‘Alternative legume crops for the southern region’ project was supported by Agriculture Victoria and the GRDC through the Victorian Grains Innovation Partnership. We gratefully acknowledge Frontier Farming Systems, Birchip Cropping Group, Southern Farming Systems, Kalyx and the Agriculture Victoria Alternative Legume technical team for conducting the field trials. Thank you also to the growers who hosted these field trials for the support provided to us throughout the project.

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