Faba bean agronomy and varieties

Take home messages

• Faba bean production has grown significantly in Victoria due to improved grower confidence with agronomy and varieties, which deliver profitable returns for the whole farming system.
• For commonly used varieties, sowing in April optimises grain yield in all rainfall zones across varying seasons, even in higher biomass production areas of the high rainfall zone (HRZ) (in the absence of lodging and when diseases are managed succesfully).
• In the HRZ of southwest Victoria, yield potential is likely to be limited at or above 25 plants/m² with any sowing date, suggesting that current practice is underutilising available light and moisture.
• To maintain a high yield potential across seasonal variability, growers should pursue growing manageably large canopies rather than trying to increase the pod-set of individual plants.
• In low rainfall areas, earlier flowering new varieties with higher yield potential and agronomic treatments that ameliorate soil constraints, like deep ripping on sands could give growers confidence to expand the area where faba bean is grown.
• Ongoing improvements in herbicide tolerance (PBA Bendoc) and disease resistance (PBA Amberley), combined with optimised agronomic management will improve economic yield and yield stability.

Background

Production of faba bean in Victoria has grown over the last 10 years from 35,000t produced from 22,000ha in 2009-10 season to 67,000t from 116,000ha in the 2018-19 season (Table 1). A peak in production was achieved in 2016-17 season with 220,000t and a peak in area sown was achieved at 147,000ha in 2017-18 season. These increases are due to improved grower confidence with agronomy and varieties which deliver profitable returns for the whole farming system. However, as illustrated by Table 1, the seasonal yield variability for faba bean is high due to a range of biotic and abiotic factors which when combined with price variability could constrain further growth and expansion.

Faba bean production across Victoria in 2020 was generally excellent with many crop yields of 4-5t/ha being reported within the medium and high rainfall zones. Unfortunately, prices have dropped dramatically from above $900/t in 2019, to less than $350/t in early 2021.

Most faba bean production occurs in the high and medium rainfall zones. However, there is increasing interest in the lower rainfall zones as new varieties with drought adaptation become available. Faba bean can be extremely profitable as a cash crop with long term average prices around $400/t, however prices can be volatile with peaks over $900/t in 2019 to a low of $220/t in 2018. An additional benefit reported by many growers is the higher growth rate of lambs grazed on bean stubbles, thereby providing additional profitability to the whole farm system. The ‘break crop’ benefits of faba bean also adds value to the following cereal crop and includes:

• Potentially, more than 100kg N/ha contributed to the following crop.
• Effective control of grass weeds.
• Effective break for many cereal foliar and root diseases.

When combined, these benefits are valued at improving yield of the following cereal crop by at least 0.5-1t/ha (Moodie et al. 2016).

To maintain a continued improvement in grower confidence to growing faba bean and support the growth in production and profitability several factors are being addressed through applied research and development activities to broaden the adaptability and improve the stability of faba bean yield. This paper presents some of the latest research findings that aim to overcome many of the key constraints across Victoria.

Table 1. Area sown and production of faba beans in Victoria from 2009-2010 to 2018-2019. (Source: ABARES, 2021).

^ABased on prices offered in Horsham in December of that season

Results and discussion

Maximising yield potential through canopy management in southwest Victoria (HRZ)

Canopy size, plant size and yield potential

A substantial dataset has been generated over numerous years of trials in southwest Victoria where canopy size has been manipulated through time of sowing and sowing rate. The results from these trials suggest that growers should change their thinking on how canopy management affects faba bean yield potential.

For a canopy to maximise yield it must capture as many resources as possible and allocate them efficiently to grains. This can be increased by management options such as sowing earlier or increasing the plant density up to the point at which crop-to-crop competition becomes excessive.

At Inverleigh in 2020, results of trials showed that as plant density increased each individual plant was smaller and supported fewer pods/plant (Table 2). On balance however, having more small plants with fewer pods/plant increased overall pods/m² at the canopy level. This resulted in a correlation between increased yield and increased plant density. This shows that crop-to-crop competition was not limiting up to 34 plants/m² (Table 2). At Rokewood in 2016, yield also increased with plant density up to 26 plants/m² (Table 3).

Table 2. Grain yield, net return and pod-set of PBA Bendoc sown on 13 April, 2020 (199mm rainfall from 1 Aug to 31 Oct), at Inverleigh with four plant densities averaged across two row spacings (20cm and 40cm, n.s. P>0.05). Net return based on production costs of $340/ha, seed cost $0.59/kg, grain freight cost of $30/t and grain price of $300/t.

Table 3. Grain yield and net return of Nura and PBA Zahra faba bean sown at Rokewood on 26 April 2016 (286mm rainfall from 1 Aug to 31 Oct), with five seeding rates. Net return based on production costs of $250/ha, $0.50/kg of seed sown and returns on grain of $240/t.

Previous research on faba bean crops from a wide range of environments shows that good growing conditions favour low plant densities by enabling high biomass production (Lopez-Bellido et al. 2005). The current grower practice in southwest Victoria is to sow between 15 and 25 plants/m², so it might be expected that 15 plants/m² would suit the high yielding years of 2016 and 2020. However, in the trials presented (Table 1 and Table 2), yield increased with higher density plantings of 26 plants/m² (Table 3) and 34 plants/m²(Table 2). These crops were sown in April which also favours crop growth compared to a later sowing in May. These results suggest a density of at least 25 plants/m² could be required to maximise the yield potential of faba bean crops sown in favourable conditions.

Research has also shown that short or poor seasons favour high plant densities of faba bean because the high plant densities compensate for the loss in canopy growth (Lopez-Bellido et al. 2015). It does not appear to cause excessive growth when resources are limited. This has been observed in ‘dry’ seasons in the HRZ. For example, in a trial at Lake Bolac in 2018 where rainfall was below average (102mm during August 1 to October 31), yield increased with an increased plant density up to 45 plants/m² and was consistently greater following a 26 April sowing date compared to a 17 May sowing date (Table 4). A similar result was obtained in 2015, which was another season with a ‘dry’ spring (66mm during August 1 to October 31), and yield increased up to 35 plants/m² with no further increase in yield at 47 plants/m² (Table 5). These results suggest that sowing in late April, rather than mid-May, and increasing the plant density up to 35 plants/m² is likely to increase grain yield potential in unfavourable seasons.

Table 4. Grain yield and net return of PBA Samira sown on two sowing dates with three sowing rates at Lake Bolac in 2018 (102mm rainfall from Aug 1 to Oct 31). Net return based on production costs of $306/ha, seed cost $0.32/kg, grain freight cost $30/t, grain price of $330/t.

Table 5. Grain yield and net return of PBA Zahra and PBA Rana sown at Westmere on 22 April, 2015 (66mm rainfall from Aug 1 to Oct 31). Net return based on production costs of $318/ha, seed cost $0.49/kg, grain freight cost $25/t, grain price of $400/t.

These disease-free trials suggest that typical commercial sowing rates of 15 to 25 plants/m² are underutilising available moisture and light resources. Although southwest Victoria is a relatively favourable environment for crop growth, individual faba bean plants are not compensating enough through high growth or pod-set at these densities for crop-to-crop competition to become limiting and penalise yield potential. Soil constraints (e.g., soil acidity), cool temperatures and/or limits of genetic potential in current varieties could also be contributing to this observation.

Regardless of seasonal conditions, earlier sowing increased yield, and increasing the sowing rate further increased grain returns despite the cost of extra seed. Within the sowing rate range of current industry practice, growers should focus on growing large canopies that fit their attitude to disease and lodging risk, while paying attention to extra seed costs and grain price variability. Trials have consistently demonstrated that late sowing or low plant densities will not compensate in yield potential through higher pod-set.

Higher sowing rates and/or earlier sowing could also add additional benefits to the farming system through greater competition with weeds, increased N fixation and increased feed availability for livestock post-harvest. These benefits should be weighed against the higher risk of lodging and disease.

Time of sowing and phenology

Early sowing generally increased crop biomass as well as enabling the key development phases of flowering and pod-set to occur earlier in the season. Compared to other pulses, faba bean are more tolerant to frost damage and cool temperatures, but more susceptible to heat damage and moisture stress. For instance, April sown trials out-yielded May sown trials in 2018, 2019 and 2020 which experienced high incidences of frost coinciding with flowering and pod-set, although the rainfall received during each spring differed.

At Lake Bolac in 2020, a time of sowing x variety trial found that across the seven cultivars tested an earlier time of sowing resulted in an increased grain yield (Table 6). AF12025 achieved the highest yield with the earliest flowering date of July 5 (compared to August 7 for PBA Samira) in the TOS1 treatment but had a lower yield than PBA Samira with a 19 May sowing date.

Faba bean breeding trials are typically sown in a window between 27 April to 19 May and this is reflected in the high yield and yield stability of the popular variety PBA Samira, and the recently released PBA Amberley. The interactions between sowing date and cultivar type for yield indicate that more work can be done to match cultivars to a wider range of sowing dates for southwest Victoria. An exploration of phenological responses of current and upcoming breeding lines was undertaken in southwest Victoria and Tasmania in 2020 in collaboration with Pulse Breeding Australia to begin understanding optimum flowering windows for these regions.

Table 6. Grain yield of seven faba bean cultivars sown on three sowing dates at Lake Bolac in 2020.

Managing herbicide residues and weed management in Victoria

Weed management and herbicide residues are important constraints to maximising the productivity and profitability of faba bean across Victoria. Leading growers have always taken a long-term view to minimise potential weed burden in faba bean by effectively controlling broadleaf weeds in the cereal phase of the rotation and utilising herbicides that are unlikely to create significant residual issues in the faba bean phase.

The faba bean breeding program has developed cultivars with improved tolerance to Group B imidazolinone herbicides. The release of PBA Bendoc in 2018, has increased options for the control of broadleaf weeds and enhanced tolerance to sulfonylurea residues. Several trials have been conducted over several years resulting in the registration of Intercept® for use in-crop. For example, in PBA Bendoc no significant visual damage was observed from the application of imidazoline products and a very low level of damage occurred from simulated sulfonylurea residues in trials at Horsham 2019 (Table 7). Further, grain yield loss was not significant in PBA Bendoc compared with the ‘Nil’ for any of the herbicide treatments, although the data indicates approximately 10% potential yield loss in the simulated residue treatment of metsulfuron-methyl compared to all other treatments. In comparison, severe crop damage and significant yield loss was observed for most herbicides applied to the conventional variety PBA Samira.

Breeding programs are continuing to develop improved tolerance to Group I (e.g., clopyralid) and Group C (e.g., metribuzin) herbicides, which will further enhance weed control and herbicide residue management options. There have also been several new herbicides (e.g. Group G) registered and recently released which will continue to improve the ability of growers to maximise weed control in faba bean and throughout the whole farming system.

Table 7. Visual herbicide damage score (0, No symptoms – 100, Crop death) and grain yield (t/ha) of the new imidazoline tolerant variety, PBA Bendoc, in comparison to the conventional variety, PBA Samira, in response to application of imidazolinone products post sowing pre-emergent (PSPE) at four node crop growth and a sulfonyl urea applied to simulate potential residuals at Horsham in 2019.

Adaptability to the LRZ of Victoria – genetic and agronomic solutions

Faba bean can be extremely sensitive to hot, dry conditions, particularly during the reproductive phase. Faba bean is also poorly adapted to deep sandy soils which are found in 20-30% of the low rainfall Mallee. Several years ago, the breeding program focussed on improving adaptation through earlier flowering and maturity, which resulted in the release of PBA Marne, which shows improved yield under drier conditions, particularly in SA. In Victoria, another breeding line, AF12025, which can flower two weeks earlier than PBA Samira, has consistently shown high grain yields in the southern Mallee across a range of cropping seasons. (Table 8). Potential gross margins were above $3,000/t in 2019 when high yields and prices were achieved concurrently.

Table 8. Grain yield (t/ha) and gross margin ($/ha) of selected faba bean varieties and breeding lines at Curyo (southern Mallee, Vic) from 2016 to 2020.

^1. Gross margins are based on estimated production costs of $300/ha.

Recent agronomic research has highlighted that practices such as deep ripping, which reduce soil penetration resistance, can lead to substantial productivity gains of pulses on these deep sands. At Koolonong in 2020, ripping to 50cm prior to sowing improved faba bean grain yield by 300% in deep sand, increasing the yield from 0.5t/ha to 2t/ha (Figure 1). The yield on the ripped sand exceeded yields on the heavier swale soil in the flat of the same paddock by approximately 0.5t/ha. These examples highlight that with ongoing agronomic and genetic improvement, further expansion of faba bean is feasible.

Figure 1. Effect of soil type and deep ripping sandy soils on the grain yield of faba bean at Kooloonong in 2020.

Genetic solutions to disease management

Diseases, notably chocolate spot, are a significant obstacle to closing the yield gap of faba bean, particularly in the HRZ. A significant step has been made with the recent release of varieties with enhanced chocolate spot resistance. For example, when plant density was increased, which increased biomass, disease increased in faba bean canopies (Figure 2). However, the rate of increase in PBA Amberley was smaller (2.3% more disease per 10 plants/m²), than PBA Bendoc (4.9% more disease per 10 plants/m²). Therefore, genetic resistance can change the relationship between canopy size and disease pressure revealing an opportunity to close the yield gap through growing profitably large canopies in the HRZ. Agronomy packages will need to be tailored appropriately to protect the higher yield potential of these large canopies, and further work is needed to clarify what that will entail. Further disease management results are discussed at this GRDC Update by Josh Fanning.

Figure 2. The effect of plant density on chocolate spot disease severity (% of canopy leaf area) evaluated on October 20, 2020 in PBA Amberly and PBA Bendoc, which differ in their genetic resistance against diseases. Error bars are the l.s.d. for the Variety x Plant density interaction (P<0.05).

Agronomic solutions to acid soil constraints

Acid soils are a significant constraint for faba bean production in southwest Victoria. Low soil pH reduces crop productivity directly by reducing nodulation and nitrogen fixation. An acid-tolerant rhizobia strain developed at SARDI has been shown to increase nodulation in these conditions. For instance, at Winchelsea in 2020 this acid-tolerant strain (SRDI969) stimulated greater overall nodulation (Figure 3). In addition to this, when the rate of inoculant was doubled, nodules increased from 27 to 37 nodules/plant. In this trial, the current commercial strain (WSM1455) did not respond to a doubled rate of peat inoculant and averaged 14.5 nodules/plant.

These levels of nodulation are however lower than the suggested optimum of 50 nodules/plant. This is because the soil pH at this site was 4.4 CaCl₂ at 0 to 20cm depth. Liming is recommended to achieve a pH of 5.5 CaCl₂ in the top 10cm of soil which will maintain soil pH above 5.0 in the top 20cm of soil. This will enable greater nitrogen fixation in addition to the other system benefits improved pH brings.

Figure 3. The effect of rhizobia strain and peat inoculation rate on faba bean nodulation at Winchelsea in 2020, compared to uninoculated and cross-contamination controls. Error bars are the Lsd of a one-way ANOVA (P<0.05).

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the authors would like to thank them for their continued support.

The authors are also grateful to all growers who have hosted trials on their farms and the input of industry representatives and colleagues to trial ideas and treatments.

Additionally, the authors are thankful to the technical teams of Agriculture Victoria and Southern Farming Systems, who have managed these trials.

Useful resources

Faba Bean Southern Region - GrowNotesTM, 2017.  Available on the GRDC website.

Online Farm Trials – All trial results from the Southern Pulse Agronomy Research program are published here.

References

ABARES Crop Report, Dec 2020. Department of Agriculture, Water and Environment, Australian Government.

Lopez-Bellido FJ, Lopez-Bellido L, Lopez-Bellido RJ, ‘Competition, growth and yield of faba bean (Vicia faba L.)’, European Journal of Agronomy 23, pp 359-378.

Moodie, M., Peoples, M., Goward, L. and Wilhelm, N. Solutions to improve nitrogen use efficiency for the world, 4 – 8 December 2016. In ‘Proceedings of the 2016 International Nitrogen Initiative Conference, Melbourne, Australia’.

Contact details

Dr Jason Brand
Agriculture Victoria, 110 Natimuk Road, Horsham, Vic. 3400
0409357076
jason.brand@agriculture.vic.gov.au
@jasonbrand

James Manson
Southern Farming Systems, 23 High Street Inverleigh VIC 3321
0488 600 509
jmanson@sfs.org.au
@TrialsofJManson