Key messages
- Trial results from Sangar are helping build a clearer picture of how companion cropping with vetch could support lower-cost nitrogen supply in grain systems, particularly in challenging seasons where input costs and seasonal risk remain front of mind for growers.
- The results reinforce the balancing act growers face in companion cropping systems — later termination can increase nitrogen contribution through greater legume biomass, but if conditions are dry, it may come at the expense of cereal yield.
- All companion cropping treatments increased soil nitrogen compared to straight wheat grown under low nitrogen conditions, reflecting the ability of vetch to fix atmospheric nitrogen and contribute to the soil nitrogen pool as residues break down over time.
Trial results from Sangar are helping build a clearer picture of how companion cropping with vetch could support lower-cost nitrogen supply in grain systems, particularly in challenging seasons where input costs and seasonal risk remain front of mind for growers.
Companion cropping is a practice where two or more different crop species are grown together in the same field, at the same time with the companion species terminated before harvest of the cash crop. The goal is for the crops to provide complementary agronomic benefit to each other during growth. It’s different from traditional intercropping in that companion cropping is often designed with one “main” crop in mind, with the companion species playing a supporting agronomic role. The 2025 replicated trial, part of the GRDC NGN project Companion cropping legumes for lower cost nitrogen supply in farming systems, explored how different vetch termination timings influenced wheat performance, soil nitrogen and grain quality under extremely dry seasonal conditions.
Termination timing refers to the point at which a companion crop is deliberately stopped during its growth cycle, for example, through spraying. It is a key management decision because timing affects how much biomass and benefit the companion crop provides — such as nitrogen fixation, weed suppression or soil cover — while also reducing the risk of competition with the main crop for water, nutrients, and light.
Despite the late sowing and decile 1 growing season rainfall, the 2025 trial demonstrated that companion cropping can improve soil nitrogen levels, although moisture stress ultimately limited the ability of wheat crops to convert that extra nitrogen into higher yields.
Seasonal conditions had a major influence on outcomes in 2025. Only 92 mm of rainfall fell between July and October, well below the long-term average, placing crops under significant moisture stress during critical growth stages. Wheat biomass and grain yield were substantially lower than in 2024 as a result.
Despite the late June sowing and decile 1 rainfall, vetch-only treatments still yielded 0.26 t/ha under low nitrogen and 0.36 t/ha under high nitrogen conditions. One of the clearest findings from the trial was the importance of termination timing.
Where vetch was terminated early in September, wheat yields were maintained at levels similar to the wheat-only low nitrogen treatment. This is because September termination most likely reduced competition between the wheat and vetch for water and nutrients, allowing the cereal crop to continue developing effectively, compared to the October termination. In contrast, leaving the vetch to grow until October before termination increased biomass production (for both wheat and vetch) and estimated nitrogen fixation, but also increased competition for limited soil moisture and resources. This was the most probable reason for the lower wheat yields seen in the later termination treatments.
The results reinforce the balancing act growers face in companion cropping systems — later termination can increase nitrogen contribution through greater legume biomass, but if conditions are dry, it may come at the expense of cereal yield.
All companion cropping treatments increased soil nitrogen compared to straight wheat grown under low nitrogen conditions.
This reflects the ability of vetch to fix atmospheric nitrogen and contribute to the soil nitrogen pool as residues break down over time.
Estimated nitrogen fixation ranged from 1.4–11.2 kg N/ha depending on termination timing, with later terminations producing more biomass and therefore greater nitrogen fixation. However, overall nitrogen contribution was relatively modest and did not translate into measurable increase in wheat yield.
The trial also highlighted the complex relationship between nitrogen, yield and grain quality. Higher yielding treatments did not always produce higher grain protein. In some cases, later terminated companion crops recorded higher grain protein despite lower yields, likely due to additional nitrogen contribution from vetch residues, combined with smaller grain size caused by dry finishing conditions.
Overall, the trial continues to demonstrate the potential for companion cropping systems to improve soil nitrogen status while reducing reliance on synthetic fertiliser. However, the results also show that success depends heavily on seasonal conditions and careful management, particularly around the timing of legume termination.
In dry seasons, companion cropping is unlikely to be a silver bullet for boosting cereal yields, but it may offer valuable nitrogen benefits and greater flexibility around nitrogen fertiliser decisions. The key takeaway from Sangar is clear: getting termination timing right is critical. When managed well, companion cropping with vetch has the potential to help growers balance input costs, soil fertility and seasonal risk in increasingly variable conditions.
Learn more by reading the full article, Companion cropping legumes for lower cost nitrogen supply – results from the replicated trials at Sanger or watch Riverine Plains Project Officer Sabita Duwal discuss the trial in Companion cropping wheat and vetch in the Riverine Plains: Trial update. You can also hear from Coreen farmer Adam Feuerherdt in the case study video, Using vetch in a companion cropping system.
NGN - Companion cropping legumes for lower cost nitrogen supply in farming systems is an investment of the Grains Research and Development Corporation.
GRDC's National Grower Network (NGN) refers to the community of growers and grains industry stakeholders across Australia’s growing regions who GRDC engages directly with to assist in developing locally relevant research development and extension (RD&E) investments.