Break crop selection in low rainfall environments – one size does not fit all

Take home messages

• Break crop performance is highly variable across the southern low rainfall zone, and therefore a ‘one size fits all’ approach does not work.
• Nuseed^® Diamond canola, PBA Samira faba bean, Volga vetch and PBA Bateman lupin have shown improved crop performance compared to other varieties of their respective crop species.
• Genesis^TM 090 chickpea, PBA Striker chickpea, PBA Bolt lentil, PBA Hallmark XT lentil, PBA Butler field pea, and PBA Wharton field pea were the top performing varieties of their respective crop species, depending on the environment.
• @RISK model analysis outcomes indicate that field peas are profitable in 40.7% of years while lentils can be profitable in 51.6% of years.

Background

Current farming systems in the low rainfall zone (<325mm) of southern Australia are dominated by cereal production. There is increasing concern about grass weed and soil-borne disease pressure, as well as diminishing soil fertility (particularly nitrogen (N)), and poor water use efficiency (WUE) as a result of continuously cropping cereals (Seymour et al. 2012; Angus et al. 2015; McBeath et al. 2015). Break crops have a key role to play in addressing these issues, as well as diversifying crop production and economic risk, and maintaining long-term sustainability of the system. The success of a break crop is critical for gaining the most benefit out of the break phase for the subsequent crops.

The use of a break crop in a cereal dominant cropping system consistently results in at least 1t/ha of additional yield in the subsequent crop, in low rainfall environments (McBeath et al. 2015) and can improve profitability of the farming system by up to $100/ha per year (Moodie and Wilhelm 2016). However, there remains a lack of information available to growers about choosing the break crop best suited to their situation, as break crop development to date has largely occurred in medium and high rainfall zones. The aim of this research is to identify the best break crop species and varieties for different climate, soil type and biotic stress situations — within major cropping regions of the southern low rainfall zone.

Method

Break crop species-by-variety trials were undertaken in 2017 at four key locations across the southern low rainfall zone — and were expanded to new locations in 2018 and 2019. A total of 14 trials were undertaken across five locations over three seasons. The trials include three to six varieties of canola, chickpea, faba bean, field pea, lupin, lentil, and vetch (Table 1) — representing potential options for the low rainfall zone. Varieties were selected following consultation with breeders, researchers, and advisors. Varietal options include herbicide-tolerant varieties and those with a potential alternative end-use to grain, such as grazing or hay.

Trial measurements include site soil characteristics, soil moisture, seasonal temperature and rainfall, grain yield, biomass yield, and gross margin (GM). Trials were sown using an experimental plot seeder. Biomass yield was measured at late flowering to early pod development growth stage to identify potential use as a hay, forage or manure crop. Trials were harvested at crop maturity using an experimental plot harvester. GM was calculated using the PIRSA Rural Solutions ‘Farm gross margin and enterprise planning guide’ and a five-year average grain price for each season.

Table 1. List of break crop species and varieties included in the trials.

The plot arrangement was a split plot design with three replicates, and random assignment of break crop species to the whole plot and variety to the sub plot. The use of this design ensures each break crop species receives appropriate agronomic management. A multi-environment trial (MET) analysis using a factor analytic model (Smith et al. 2001), with adjustment for design factors and spatial variation, was conducted for biomass and grain yields. Models were fitted in ASReml-R (Butler et al. 2009) in the statistical software platform R.

A model developed by Rural Directions Pty Ltd using @RISK, (an add-on to Microsoft Excel), to assess risk and net profit associated with different break crop options in a three-year break-wheat-wheat rotation. The model included percentile 10, 50 and 90 yields and prices (Table 2), together with low-input variable costs for each crop — analysing 5 000 seasonal outcomes. Grain yield percentiles were calculated from actual grain yield results from break crop species by variety trials, 2017 to 2019. Grain price percentiles were calculated from long-term commodity price records, based on farm gate prices. Estimated yield benefits and penalties associated with the following crop, and estimated fixed costs (depreciation, finance cost and overhead costs) were also accounted for in the model.

Table 2. Grain price and yield percentiles used in the @RISK model analysis.

Results and discussion

Break crop and variety selection

The MET analysis identified strong correlations for grain yield, biomass yield, and GM between some environments, as well as negative and weak correlations — demonstrating the high variance across the low rainfall environments. Break crop species production was variable, with some species showing improved stability in some environments. In most environments, in particular at Minnipa on the upper Eyre Peninsula (EP), field pea expressed their reliability and stability in low rainfall environments, providing that they are not sown in a frost prone area. Alongside field pea, at Willowie in the upper Mid-North, lentil and vetch have shown stability and reliability. In the northern Victorian Mallee, west of Mildura, canola and chickpea have shown stability across two highly variable seasons.

The MET analysis also identified varieties in each break crop species that were consistent performers for their relative crop species. Nuseed Diamond canola is a fast growing and early maturing hybrid variety, and with these characteristics has been the top performing canola variety for both grain and biomass yield across all environments. Hybrid Clearfield^® canola varieties Pioneer 44Y90 and Pioneer 43Y92 have proven to be the next best performers compared to Nuseed Diamond— and would be suitable options where weeds or herbicide residues are an issue.

Open-pollinated canola varieties did not perform as well as hybrid varieties in the low rainfall environments of this study. PBA Samira faba bean performed well for both biomass and grain production across all environments, and generally similar to, or slightly better than, PBA Marne (a low rainfall or short season adapted variety). However, if herbicide residues and or particular broadleaf weeds are an issue, PBA Bendoc with improved tolerance to Group B herbicides residues is a suitable option.

Sowing time may also dictate faba bean variety selection, as PBA Samira would be better suited to early sowing than PBA Marne. Early maturing vetch variety, Volga, has high grain and hay yield potential, and has proved to be a top performing vetch variety across the low rainfall environments. PBA Bateman, a recent high yielding lupin variety release with early flowering, has been a consistent performing variety for lupin. Desi chickpea, PBA Striker, and kabuli chickpea, Genesis^TM 090, showed improved biomass and grain yield performance, as well as improved early vigour and ground cover compared to large-seeded kabuli chickpea, PBA Monarch.

For field pea, PBA Butler and PBA Wharton were high yielding varieties compared to other field pea varieties included in the study. Despite yield being similar for these two varieties, the more recently released variety PBA Butler showed improved early vigour and canopy structure over PBA Wharton in some environments. Performance of both semi-leafless (SL) and conventional (C) field pea types were studied across the low rainfall environments to look at alternative end-use options to grain production. However, C type field pea did not offer improved biomass production over SL types (Figure 1). Additionally, C type field pea has poor lodging resistance, and therefore SL varieties may be a more suitable option, regardless of end-use.

PBA Bolt and PBA Hallmark XT lentil varieties performed well across all environments for both biomass and grain production. PBA Bolt offers early to mid-flowering and maturity, lodging resistance, improved tolerance to boron and salt, and high grain yield potential in drought conditions and low rainfall environments. PBA Hallmark XT has improved herbicide tolerance compared to conventional lentil varieties — and would be well suited to areas or seasons where Group B herbicide residues are an issue.

Figure 1. Growing conventional field pea varieties PBA Coogee and PBA Percy does not offer improved biomass production over semi-leafless (SL) varieties in the low rainfall zone of South Australia (SA). In 2018, Minnipa, Willowie, Warnertown and Pinnaroo environments are positively correlated for biomass production (0.43-0.9).

@RISK analysis

The @RISK analysis of 5000 seasonal outcomes provided a percentage of years that each break crop would be profitable, and the net profit for each rotation sequence (Table 3). Average net profit per hectare, per year, over a three-year rotation for chickpea and lentil were $181.86 and $72.71, respectively, compared to $4.40 for field pea. On average over all seasons, rotations with faba bean and canola produced losses of $10.32 and $44.19.

Rotation sequences including field pea were profitable 40.7% of years and those including lentil were profitable in 51.6% of years. Sequences that included chickpea were profitable in 55.5% of years. It is important to keep in mind that this analysis was based on a low input system with the application of only one fungicide spray, and chickpea would not be as profitable in a season with high disease risk or infection of ascochyta blight. The analysis indicated that canola and faba bean were the least profitable, and were relative high risk break crop options — and were only profitable in 34.3% and 38.7% of years, respectively.

Table 3. @RISK analysis of break crop options in a three-year rotation with wheat. The rotation sequence is ranked from lowest risk and most profitable, to highest risk and least profitable.

Net profit = gross margin minus estimated fixed costs ($100/ha)

Conclusion

The decision to grow a break crop is generally done with a whole systems approach, as break crops can be utilised to address the issues and constraints that arise from continuously cropping cereals. The choice of break crop is made depending on the reason for growing a break crop, crop end-use, financial risk, paddock selection, and soil type.

Field pea production is more stable than other break crop species across the low rainfall environment. However, field pea is a risky option for grain production where spring frost events occur frequently. Field pea have multiple end-uses to grain, and with high biomass potential can be utilised as a hay, forage, silage, or manure crop when frost or drought affected, to salvage a financial return.

Vetch is also a versatile crop, having multiple potential end-uses, and is a good fit in a mixed farming system. Lupin is suited to sandy or acidic soils and has potential to be utilised as a green-brown manure crop.

Canola, lentil, and faba bean can provide herbicide tolerant crop options where in-crop weeds or herbicide residues are an issue. Canola also has a good fit where cereal root diseases are limiting production (Kirkegaard et al. 2008). However, canola requires adequate soil moisture at sowing for successful germination, particularly on heavier soil types and may be an opportunistic crop in some environments. Lentil is more sensitive to soil constraints than other break crop species and plant height is often low, leading to poor harvestability. Faba bean may be suitable where a break crop is needed in a frost prone area, as faba bean tolerate reproductive frost events better than other pulse crop species, providing that there is an early break to the season.

Chickpea have shown stability in the upper Victorian Mallee. However, it is important to consider the ability to manage disease.

Each break crop species has its own unique fit in the farming system, and all available agronomic, local, and paddock information needs to be taken into consideration when selecting a break crop to fit into each individual farming system. Each break crop species has several suitable varieties, with a range of agronomic characteristics to select from, that are suitable to production in the low rainfall environment. Although top performing varieties have been identified for some break crop species, the final selection will depend on the individual farming system — particularly where soil type, herbicide residues, and or broadleaf weeds are a constraint to production.

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 continued assistance in trial management from SARDI Agronomy groups at Clare and Minnipa, as well as Frontier Farming Systems, is gratefully acknowledged and appreciated.

Useful resources

'A systems approach to break crop selection in low rainfall environments' - Sarah Day for the 2019 Agronomy Australia Conference

'Break crop production in southern low rainfall environments' - Sarah Day for Farming Systems 2018 Summary

Break Crop Production In Southern Low Rainfall Environments - Mallee Sustainable Farming

Upper North Farming Systems Annual Research and Extension Compendium 2017

References

Angus, J.F., Kirkegaard, J.A., Hunt, J.R., Ryan, M.H., Ohlander, L. and Peoples, M.B. (2015) Break crops and rotations for wheat. Crop and Pasture Science 66(6), 523-552.

Butler, D., Cullis, B., Gilmour, A. and Gogel, B. (2009) ASReml-R reference manual. (Toowoomba, Australia.)

Kirkegaard, J., Christen, O., Krupinsky, J. and Layzell, D. (2008) Break crop benefits in temperate wheat production. Field Crops Research 107(3), 185-195.

McBeath, T.M., Gupta, V.V.S.R., Llewellyn, R.S., Davoren, C.W. and Whitbread, A.M. (2015) Break-crop effects on wheat production across soils and seasons in a semi-arid environment. Crop and Pasture Science 66(6), 566-579.

Moodie, M. and Wilhelm, N. (2016) Profitable crop sequence in the low rainfall regions of south eastern Australia. GRDC Project (DAS00119) Report.

Seymour, M., Kirkegaard, J.A., Peoples, M.B., White P.F. and French, R.J. (2012) Break-crop benefits to wheat in Western Australia & insights from over three decades of research. Crop and Pasture Science 63(1), 1-16.

Smith, A., Cullis, B.and Thompson, R. (2001) Analyzing variety by environment data using multiplicative mixed models and adjustments for spatial field trend. Biometrics57(4), 1138-1147.

Contact details

Sarah Day

70 Farrell Flat Road, Clare SA 5453

08 8841 2404

sarah.day@sa.gov.au

@Sarah_Day_