Agronomy and recent research relating to High Rainfall Zone (HRZ) faba

Take home messages

• With appropriate management, faba beans can be a profitable grain crop with significant benefits for the farming system. However, the Tasmanian market for faba bean grain is currently very small.
• Faba beans fit Tasmanian farming systems as either an autumn- or spring-sown option, having achieved high grain yields of 5 to 7 t/ha with irrigation in small-plot trials with both sowing windows.
• The primary constraints to HRZ faba bean production include a soil pH of less than 5.5 CaCl₂, chocolate spot infection in large canopies and challenges with broadleaf weed management. However, progress has been made in addressing each of these in recent years.
• Sowing early and/or with higher plant densities are practices that increase yield potential as well as the risks of chocolate spot infection and lodging.

Background

Faba bean production has increased in Victoria in the last ten years, from 22,000ha sown in 2010 to 116,000ha sown in 2019 (Brand and Manson, 2021). This can be attributed to an increase in grower confidence in faba bean management based on agronomic research and the release of new varieties that have reduced its historically high yield variability. There is also a much greater appreciation for the system benefits faba beans provide to the rotation.  Mainland faba beans have high price volatility. Grain price for faba beans was $220/t in 2018 and $900/t in 2019, with the long-term median at $300/t (Brand and Manson, 2020).

The area sown in Tasmania to faba beans, or related sub-species such as tick beans, is very small due to a limited market, however opportunities in supplying faba beans as a source of protein for fish feed could develop soon.

This paper will cover basic considerations in growing faba beans in the High Rainfall Zone (HRZ) including an update on recent research.

The potential contribution of faba beans to HRZ profitability

Pulses provide significant benefits to crop rotations by acting as a disease break, providing alternative weed control opportunities and by fixing atmospheric nitrogen (N) that supplements the crops requirements and increases soil N fertility for following crops.

Of the temperate pulses, faba beans are particularly well adapted to HRZ environments. Primarily this is due to their relative ability to withstand periodic waterlogging (Pampana et al.2016, Solaiman et al. 2006). The downside of this adaptability to environments with moist soil is that they are highly susceptible to drought stress and can suffer significant yield penalties with dry springs on the mainland. They are also relatively susceptible to heat stress but tolerate frost.

Another feature that makes faba beans suited to the HRZ is that they are capable of high biomass production that is produced on a relatively high proportion of nitrogen fixed from the atmosphere (Pampana et al. 2018). This makes a significant contribution to the soil N fertility that appears to be required to close the wheat yield gap in this environment (Warren et al. 2019). Other pulses produce less biomass and/or are less reliant on N fixation if soil fertility is already high (Rose et al. 2016).

It is common practice in mixed farming systems in Victoria to graze faba bean stubbles with lambs. They will gain weight if there are at least 10 faba bean grains/m² on the ground after harvest (Cam Nicholson, personal communication) and growers report significant profitability from the practice. The income generated by grazing, the increase in subsequent grain yields due to greater soil N fertility, improved weed control and a disease break, all build potential for a profitable faba bean phase in a growers crop rotation.

Apart from the benefits contributed to the farming system, faba beans themselves can be highly profitable in the HRZ. Typical variable costs are around $400/ha in Victoria, requiring a break-even yield of 1.25 t/ha at the median grain price of $300/t. Growers report that dryland HRZ faba bean yields have ranged from 1-5 t/ha in the last ten years.

At Cressy, Tasmania, in 2020, a mean grain yield of 8.0 t/ha was achieved with irrigation at 23 plants/m² for three varieties sown on May 15 (Table 1). Up to 4.5 t/ha was achieved at 28 plants/m² for the same varieties sown on September 11. The spring-sown trial received sub-optimal irrigation because it was in an autumn-sown paddock that did not receive irrigation after the grower’s crop reached maturity hence greater grain yields for spring-sown faba beans are possible. A trial that was sown on August 29, 2019, achieved 6.9 t/ha with adequate irrigation. Therefore, both autumn and spring sown options have the potential to be highly productive in Tasmanian systems.

Yield data from a wider range of seasons is available from rainfed trials in southwest Victoria, where yields have varied from 7.8 t/ha to 1.2 t/ha (Kreeck and Manson 2019). These results are from small-plot trials on sites selected for more favourable soils. Average paddock yields tend to be 25% less than these values. Where irrigation is available in Tasmania the risk of low yields from moisture stress will be reduced, but heat stress events (>35°C) during reproduction can still cause low yields.

Table 1. Mean effect of plant density on the grain yield of three faba bean varieties sown on May 15 or September 11 in 2020.

Key factors for success

Nodulation

Approximately 50 nodules per plant is considered optimal for faba bean nitrogen fixation and growth. High nodulation is achieved with favourable soil conditions and best practice inoculation. Successful inoculation of faba bean roots generally improves grain yield as well as the contribution of atmospheric N that it makes to the farming system.

Many factors affect the success of inoculation, and these are summarised elsewhere (see Useful Resources below). Low pH is a particular challenge that has been addressed recently in Victoria. For example, double rates of inoculant can improve nodulation and grain yield in hostile conditions. At a trial site in Winchelsea with a pH of 4.4 CaCl₂ and low background rhizobia numbers, faba bean grain yield was increased from 2 t/ha to 4 t/ha (P<0.05) in 2020 by inoculating with double the recommended inoculant rate (Duff and Manson 2020, see also Online Farm Trials when published online). A new acid-tolerant strain of rhizobia has been tested that increased nodule number at the same site in 2020 from 15 to 32 nodules/plant and increasing grain yield by about 1 t/ha (P<0.05) (Duff and Manson 2020, see also Online Farm Trials when published online). This new acid-tolerant strain will be potentially released in 2022 (Ross Ballard, personal communication).

Favourable soil conditions enable the rhizobia bacteria that form nodules on faba bean roots to persist in the soil at high numbers between growing seasons. Constraints such as low soil pH (<5.5 CaCl₂) reduce rhizobia survival and lead to low background numbers at sowing when nodulation occurs. A new DNA-based test, PREDICTA® rNod, is available through PREDICTA® B accredited agronomists that measures the amount of rhizobia present in soil before sowing (Ballard et al. 2021). If there are high rhizobia numbers before sowing there is less risk of nodulation failure, and vice versa. This information can be used to adjust practices such as liming and the number of years between faba beans in a rotation to maintain higher background rhizobia numbers, and to inform inoculation strategies in the upcoming season.

Weed control

Faba bean yields can be significantly reduced by weed competition so care should be taken to sow them into clean paddocks. Furthermore, faba beans are susceptible to several residual herbicides used in preceding cereal crops, so refer to the label plant back periods and plan accordingly.

Managing broadleaf weeds has been a challenge in faba beans with limited herbicide options. Terbuthylazine (Terbyne, Group C) is commonly used, and fomesafen (Reflex®, Group G) has recently been registered for pre-emergent and post-sowing pre-emergent applications. Intercept® (imazamox and imazapyr, Group B), is registered as a post-emergent application in Imidazolinone (imi) tolerant faba beans including the new high-yielding variety PBA Bendoc. This is the first post-emergent broadleaf weed control option to be available in faba beans. The release of this herbicide tolerant variety, with more in the breeding pipeline, will improve weed control options and reduce obstacles to incorporating faba beans into rotations.

Faba beans also provide an opportunity for a crop-topping tactic which is important because weed seed set is a key target for weed control in non-cereal phases of rotations in the HRZ. A long-term trial at Lake Bolac that had three herbicide strategies applied (Figure 1) which showed that when there were three cereal phases out of four from 2012 to 2015 weed numbers increased exponentially due to there being no options to control the weeds that survived pre- and post-emergent herbicide applications. However, a double break using faba beans followed by canola in 2016 to 2017, in which both were crop-topped, brought weed numbers back to pre-2015 levels and degraded the weed seedbank with a long-term effect.

Figure 1. The effect of herbicide strategy on ARG seed heads/m² in a nine-year trial at Lake Bolac. “W” is wheat, “B” is barley, “C” is canola, “FB” is faba beans. Differences in seed heads/m² between herbicide strategies are significant (P<0.05) in every year except 2017.

Disease control

Three fungal diseases are the main concerns for faba beans in southern Australia: Ascochyta blight, cercospera, and chocolate spot. With the improved genetic resistance of newer varieties, Ascochyta blight and cercospera tend to be minor diseases in most seasons and are generally controlled with a fungicide application at the four-node stage, often applied with the grass weed herbicide application.

Chocolate spot infections can be severe in wet springs and cause significant yield penalties. This occurred in disease management trials at Lake Bolac and Lake Linlithgow (near Hamilton) where every 1% of canopy leaf area affected by chocolate spot symptoms decreased yield by an average of 80 kg/ha in 2020, a year with an estimated yield potential of 9 t/ha.

Figure 2 presents the grain yield results from these trials, in which the combinations of variety, fungicides and plant density were tested for disease management. PBA Amberley, rated MRMS for chocolate spot, yielded much more than PBA Bendoc, rated MS, at Lake Linlithgow in all treatments, but the varieties were equal at Lake Bolac when fungicides were used. Lake Linlithgow is a wetter environment and had greater disease pressure, causing a large difference in grain yield between the varieties. Fungicides increased grain yield even though a delayed application caused by poor spray conditions meant that they were not successful in preventing an infection, but rather reduced its severity. Increasing plant density from 15 to 25 plants/m² had no yield penalty at Lake Linlithgow, and a 10% yield penalty at Lake Bolac.

The results show that PBA Amberley is more suited than PBA Bendoc to situations where there will be large canopies in high disease pressure years due to its greater genetic resistance. Where poor fungicide control occurs in a wet spring the yield penalty from increasing the plant density from 15 to 25 plants/m² is small.

Figure 2. Grain yield of a sowing rate x variety x fungicide trial at Hamilton (a) and Lake Bolac (b). “ * “ means P<0.05, “ ** “ means P<0.001, “ *** “ means P<0.001, and “ns” means P>0.05.

Chocolate spot symptoms develop rapidly from when first observed and it is unlikely that fungicides will eliminate the disease once it has established. Therefore, strategic prevention based on environmental conditions is currently the best strategy for faba bean disease management, however this is being investigated further in 2021. Canopy closure appears to be an important timing for a fungicide application. For example, in a small-plot trial in 2020, a treatment with a cheaper fungicide program yielded 0.8 t/ha greater than a more expensive strategy because it had an early canopy closure spray, compared with at flowering in the more expensive strategy.

New fungicide products have become available in recent years that have greater efficacy for disease management. Care should be taken to rotate fungicide groups to reduce the development of resistance.

Grain quality

Grain quality is an important factor for grain price in all pulses destined for human consumption. Faba beans that are large with a lighter colour and free from staining are necessary for exported grain. Disease, temperature stress and adverse harvest conditions can reduce grain quality.

Agronomy options

New varieties

Until recently, the most common varieties grown in Victoria were PBA Samira and PBA Zahra. More recently, PBA Amberley has been released with a higher resistance rating to chocolate spot than Samira and Zahra. PBA Bendoc is another new release with a herbicide tolerance trait, with Intercept® registered for use as a post-emergent application to control broadleaf weeds. Uptake of PBA Amberley and PBA Bendoc is increasing. The yield potential of these four varieties is about 10% greater than PBA Samira and Zahra.

Sowing date

The traditional sowing window in Victoria has been from Anzac Day to mid- to late May. However, several trials suggest that earlier sowing increases grain yield. This appears to be partly due to shifting the flowering time to earlier in the season when conditions are more reliably cool with good soil moisture, and partly through increasing biomass. For example, at Lake Bolac in 2020, seven cultivars yielded 5.5 t/ha when sown on April 9, 4.4 t/ha when sown on April 27, and 3.3 t/ha when sown on May 19 (P<0.05).  There was a trend where an earlier initiation of flowering was positively related to grain yield (Figure 3). Earlier sown treatments had larger canopies and greater lodging. Greater biomass will entail more disease pressure from chocolate spot and a greater risk of lodging, so a compromise between yield and risk may be needed.

Figure 3. Relationship of 50% flowered date to grain yield of seven faba bean cultivars sown on three dates at Lake Bolac in 2020.

Plant density

In favourable seasons, faba bean growth is promoted and fewer plants are required to maximise yield potential. However, in less favourable conditions a greater plant density will increase yield potential (Lopez-Bellido et al. 2005). This is reflected in research undertaken in 2000 to 2002 in Tasmania, in which faba bean yield of Fiesta responded to an increase in plant density from 20 to 30 plants/m² in the less favourable season of 2000 but did not respond in the more favourable season of 2001 (Dean and Mendham 2003). Increasing plant density up to 23 plants/m² increased grain yield in autumn- and spring-sown faba beans at Cressy in 2020 (Table 1). There was no significant increase in grain yield above this point, although as expected the non-significant response was more prevalent in the shorter-season spring-sown trial.

While increasing faba bean plant density above 20 plants/m² may increase yield potential, the potential increase in profitability will be constrained by extra sowing seed cost, logistical challenges at sowing from high volumes of seed, and increased risks of chocolate spot and lodging. A partial budget, like that presented in Table 2 below, can be used to assess the profitability of increasing plant density for a given farming system. The calculations in Table 2 suggest that an increase of plant density from 15 (current standard practice) to 25 plants/m² will generally be profitable in southwest Victoria with the assumptions described in the table. However, the increase in plant density in Table 2 required the sowing rate to increase by 72 kg/ha and this may not be achievable with all seed drills.

Table 2. The range of estimated profitability ($/ha, extra income less extra costs) from increasing plant density from 15 to 25 plants/m² in rainfed faba bean crops in southwest Victoria, depending on yield response (t/ha extra yield) and grain price ($/t of grain sold).

NB: Grey shading indicates the median grain yield response in SFS trials, and the long-term median grain price (Geelong).

* Assumed extra costs (for illustration purposes only): $43.2/ha to increase the sowing rate by 72kg ($0.60/kg seed), a 20% increase in sowing costs worth $10/ha ($50/ha est. sowing cost), a 20% increase in harvests costs worth $20/ha ($100/ha est. harvest cost), a freight cost of $25/t and end point royalties of $4/t. Extra fungicide costs are not accounted for.

**The range of yield responses observed in SFS trials in SW Vic, 2015 to 2020.

Row spacing

Trials testing the effect of row spacing on yield in the HRZ generally show that row spacings of 20cm and 40cm are equivalent. This was the case in Inverleigh in 2020, where increasing plant density had the same effect at the two row spacings (Figure 4). The benefits of wider row spacing include reduced machinery costs at sowing due to a greater ability to retain stubble after high-yielding years and could assist with fungicide penetration. It may however compromise on crop competition, allowing weeds such as annual ryegrass to set more seed. Wide row spacings also tend to be more susceptible to lodging, perhaps requiring a lower plant density to reduce plant height but sown earlier to maintain yield potential (GrowNotes 2017).

Figure 4. Effect of plant density on faba beans sown at 20cm or 40cm on April 13, 2020 at Inverleigh, Victoria. Different letters indicate a significant difference according to the LSD for plant density (P<0.05).

Windrowing

To reduce logistical challenges at harvest, some growers in Victoria windrow beans after desiccation. This can improve harvestability and reduce harvest losses, especially of large crops prone to lodging.

Conclusion

Faba beans have a high yield potential and provide valuable system benefits to a cropping rotation. Recent advances in breeding and agronomy have led to higher yields and greater yield stability, supporting an increased uptake of the pulse in Victorian HRZ cropping systems. Should market opportunities arise in Tasmania, growers can benefit from the work already done in the state and the work done in the Victorian HRZ to fast-track the development of the crop into a highly valuable component of cropping rotations.

Acknowledgements

The research undertaken as part of these projects is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the author would like to thank them for their continued support. Thanks also to Dr Jason Brand of the Southern Pulse Agronomy program at Agriculture Victoria Horsham for his mentoring and guidance, and to the team at Southern Farming Systems for trial management and their contributions to the interpretation of the findings.

Useful resources

GRDC Faba Bean Southern Region – GrowNotes™ 2017

Inoculating Legumes: A Practical Guide

Paddock Practices: 10 Dos and Don’ts when inoculating legumes

References

Ballard R, Barnett S, Giblot-Ducray D, Herdina, Hill K, Farquharson E and Mckay A (2021) New tool to predict the likelihood of an inoculation response to Group E and F rhizobia. GRDC Grains Research Update Bendigo 2021 Proceedings, New tool to predict the likelihood of an inoculation response to group E and F rhizobia

Brand J and Manson J (2021) Faba bean agronomy and varieties. GRDC Grains Research Update Bendigo 2021 Proceedings, Faba bean agronomy and varieties

Dean G and Mendham N (2003). Optimum plant densities for faba bean cv Fiesta VF sown on raised beds. Proceedings of the 11th Australian Agronomy Conference

Duff G and Manson J (2021) ‘Improving faba bean performance on acid soils’, Southern Farming Systems Results Book 2020, 53-58.

Kreeck G and Manson J (2019) The story so far: sowing rate influences on faba bean performance in the HRZ, Southern Farming Results Book 2018, 59-61.

Lopez-Bellido FJ, Lopez-Bellido L, Lopez-Bellido RJ, (2005) Competition, growth and yield of faba bean (Vicia faba L.) European Journal of Agronomy, vol 23, pp 359-378.

Pampana S, Masoni A, Arduin, I (2016), Response of cool-season grain legumes to waterlogging at flowering. Can. J. Plant Sci. 96, 597-603.

Pampana S, Masoni A, Mariotti M, Ercoli L, Arduini I (2018). ‘Nitrogen fixation of grain legumes differs in response to nitrogen fertilisation’, Exp. Agric. 54, 66–82.

Rose, T.J., Julia, C.C., Shepherd, M., Rose, M.T., Van Zwieten, L (2016). Faba bean is less susceptible to fertiliser N impacts on biological N2 fixation than chickpea in monoculture and intercropping systems. Biol. Fertil. Soils 52, 271–276. https://doi.org/10.1007/s00374-015-1062-8

Solaiman, Z., Colmer, T.D., Loss, S.P., Thomson, B.D., Siddique, K.H.M., 2007. Growth responses of cool-season grain legumes to transient waterlogging. Aust. J. Agric. Res. 58 406–412. https://doi.org/10.1071/AR06330

Warren D, Poole N, Wylie T, Straight M, Fuhrmann K, Midwood J, Herbert I (2019), Hyper yielding cereals – are extra inputs needed and if so, do they pay? GRDC Grains Research Update Campbell Town 2019 Hyper yielding cereals-are extra inputs needed and if so, do they pay?

Contact details

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