Increasing the profitability of double break crop rotations using a high value legume in the Wheatbelt of WA

Mar 01,2024 Technical Article, 2024, Projects,

By Nathan Craig, WMG Chief Executive Officer

Key messages

Double break crop sequences can be more profitable than current canola-cereal sequences.
Early sowing can be a significant driver of profitability for chickpea, especially mid-April sowing.
Weed populations increased in the chickpea phase but did not cause issues in the following cereal crop.

Background

Break crops are widely acknowledged as being necessary to manage the biological constraints that reduce cereal crop production. However, one of the constraints in the use of break crops is that the Gross Margin of the commonly used break crops are generally less than growing a cereal crop. To combat severe biological constraints to crop production (high weed population and/or soil pathogens) break crops have traditionally been used as a single crop in rotation. The use of two break crops in sequence has been shown to improve the effectiveness of this approach, particularly as shifts in disease presence, and increases herbicide resistance in weeds has reduced the effectiveness of a single break crop. However, the use of break crops is limited to situations where the biological constraint has a greater impact on profitability relative to the lower profitability (Gross Margin) of the break crop.

The most desired traits of a break crop are to be highly effective in controlling weeds and soil pathogens while also being highly profitable. Current highly effective break crop options of canola and lupin are rated as moderate to low profitability (respectively) by growers, while pasture phases or fallow period generally result in a low or negative Gross Margin.

This study investigated the profitability of growing canola (with effective weed control options) followed by a high value legume (with higher economic value) as an effective and profitable double break crop sequence. The contribution of an early sowing date versus a traditional sowing date to further increase the profitability of the high value legume was also evaluated.

Methodology

The double break crop sequence was evaluated at 6 demonstration sites (no replication) over three years in the Western Australian Wheatbelt region. An existing paddock of canola or fallow (depending on rainfall zone) was selected to grow a high value legume and then follow this with a cereal crop on a wide range of soil types that are prevalent across the region. Crop growth was monitored along with grain yield, and the Gross Margin was calculated to give an overall return on the three-year crop sequence. Rainfall at most sites had a combination of a below and above average seasonal rainfall that impacted on the growth and grain yield of either the double-break crop or the following cereal crop, but not both.

Results

**Figure 1.** Cumulative Gross Margin over three years for each double-break crop rotation at each site compared to current practice (dark bars) in this study. Sites presented contained 3 years of data to include the first and second break crop, followed by cereal. Ca=Canola, Ch-L=Chickpea-Late sown, Ch-E=Chickpea-Early sown, L-L=Lentil-Late sown, AL=Albus Lupin, FP=Fieldpea, Fa=Fallow, W=Wheat, B=Barley, O=Oats.

There was large variation between sites for the Cumulative Gross Margin of the double-break crop sequence of Canola (or Fallow) followed by a legume and was reflective of the range of annual rainfall and grain yield potential for each site (Figure 1). Within each site, a strong trend was that the inclusion of a double-break crop led to a similar or greater cumulative Gross Margin over the 3-year period. Within the double-break legume phase, the early time of sowing tended to give an increase in grain yield for chickpea and this was a significant driver of the increase in Gross Margin. Some sites were discontinued after the high value legume year following poor crop growth and this resulted in a lower two-year Cumulative Gross Margin compared to growing wheat after a single break (data not presented).

**Figure 2.** Gross Margin of cereal crops following a double-break for all sites that completed the 3-year crop sequence. Dark bars denote current practice for each site. Sequence abbreviations: Ca=Canola, Ch-L=Chickpea-Late sown, Ch-E=Chickpea-Early sown, L-L=Lentil-Late sown, AL=Albus Lupin, FP=Field pea, Fa=Fallow, W=Wheat, B=Barley, O=Oats.

The was a trend that the Gross Margin of cereal crops was improved in the third phase of the crop sequence following a double break crop sequence (Figure 2). There was no consistent trend in the effect of time of sowing for chickpea on subsequent cereal grain yield, however, the Gross Margin and grain yield were increased by the preceding legume crop when the legume grain yield was low, independent of the time of sowing.

**Figure 3.** Comparison of early sown (left) versus late sown (right) chickpea at Wickepin on the 17^th August, 2021. The alternate plot can be seen in each photo for reference as well as tree in left of both pictures. Photo: Amy Bowden (Facey Group).

There was also a trend that the total weed population in the third-year cereal or second-year legume were higher after the double break crop sequence compared to standard practice of growing two cereal crops following canola or fallow (when measured at GS.30 growth stage for cereals) (data not presented). The use of canola or fallow as the first crop in the double break sequence appeared effective at lowering weed numbers, while weed populations tended to be higher in the high value legume year. Weed control in the cereal crop year appeared effective in ensuring that weed populations do not get out of control as total weed population was around 50 plants/m² for double break crop sequences.

The impact of double break crop sequences on the four main soil pathogens in WA was not clear in this study (data not presented). The level of soil pathogen varied between sites and years, with the major soil pathogens being P. neglectus and R. solani AG8. Within each site, there was evidence that each crop sequence had a greater impact on changing the relative proportions of soil pathogens rather than an overall reduction in pathogen levels. The structure of this study limited the collection of soil pathogen data prior to the double break being implemented.

Discussion

This study has shown that a double break crop sequence can be more profitable than a single break where a high value legume (chickpea) can be successfully grown across the Wheatbelt of WA. This was shown across a range of soil types and rainfall zones in this study, with a key outcome being that chickpea were successfully grown in soil types and regions that were not considered to be suited to growing this legume crop. The early seeding of a high value legume in Mid-April rather than Mid-May was an effective practice to increase grain yield and drive profitability of the legume compared to the late sowing timing for every paired sowing date. It appears that the potential for chickpea to be a profitable break crop is underestimated in WA with the current agronomy packages and genetic material available.

A double break crop sequence can be a profitable option for growers in the Wheatbelt region of WA to boost the both the following cereal crop and be profitable in each year of the crop rotation. This benefit to the productivity of cropping in this region is based on the amelioration and removal of soil constraints that have previously impeded the growth of chickpea on soils other than heavy clay types. Strategies have been employed by growers over the past 10 years to remove soil compaction (deep ripping), soil water repellence (rotary spading, mouldboarding), and soil acidity (lime application). The result is a soil that is no longer inhospitable for chickpea and lentil growth. It is, however, difficult to estimate the amount of land that has been effectively ameliorated in the past 10 years where all constraints are now removed. While the focus of soil amelioration has been on the impact of these practices on wheat production, perhaps the most significant benefit for grain production from the removal of soil constraints may be the ability of growers to now diversify their crop options to further improve profitability with a lower risk of failure. Through this study and other related projects, chickpea production on other soil types has been de-risked for adoption by the practice of early sowing, which has been shown to increase grain yield on a range of soils in the Wheatbelt region, from deep coloured sands to sandy loam and clay soils.

While by no means conclusive, the data collected in this study indicates that weed populations are likely to increase in the legume phase of the double break sequence, but this does not cause a weed ‘blowout’ in the subsequent cereal crop. A barrier to successful weed control was encountered in this project where we found very limited knowledge among agronomic advisors on how to successfully grow high value legumes, especially in applying effective herbicide packages using the new chemical options now available.

More Information

Contact WMG for a copy of the full report, visit the GRDC website, or via https://www.farmtrials.com.au/

Acknowledgements

This project was a GRDC investment which was led by the West Midlands Group over the 2020-2022 period in collaboration with the Liebe Group, Facey Group, and Corrigin Farm Improvement Group. We thank all the growers who contributed to this project.