Vetch end use and how it affects the cropping rotation

Demi Taylor
administrator
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Results from BCG’s vetch agronomy trial have been released for 2023, and key messages from the Kinnabulla and Ouyen trials highlight that: 

  • Varieties Morava and Volga produced the most grazing biomass and highest hay yield.  
  • Delaying the brown manure termination timing by 4 to 6 weeks doubled biomass production.  
  • Gibberellic acid (GA) had no yield benefit for grazing or hay production.  

Varieties Morava and Volga produced the most grazing biomass and highest hay yield: 

At the Kinnabulla trial site, Morava and Volga had the highest hay yields at 6.04 and 5.49t DM/ha respectively. At the Ouyen site, there were no significant hay yield differences between varieties. 

Furthermore, statistical analyses showed a significant difference between grazing biomass produced for varieties, Morava and Volga compared to Studenica at the Ouyen trial. This differed from the grazing biomass produced at the Kinnabulla trial, where there were no significant differences. 

Overall, Morava performed well throughout 2023. Volga has shown its versatility, as an early maturing variety it has performed similarly to Morava (late maturing) and recovered well from grazing. Studenica’s performance was sub-optimal compared with the other varieties, which is reflective of it being a very early maturing cultivar in a longer-than-average season

Delaying the brown manure termination timing by 4 to 6 weeks doubled biomass production: 

There were large differences in the amount of biomass left behind between the early and late brown manure termination timings. An additional 4.79t DM/ha and 3.49t DM/ha was measured at Ouyen and Kinnabulla respectively in the later termination timing. Although there is a large variation in variety maturity, the only difference in variety performance across both sites was less biomass in the late termination timings of Studenica at Kinnabulla than Volga and Morava. 

The results demonstrate that relaying the termination timings by four to six weeks significantly increased biomass left behind, and although not reflected in the immediate soil results it could result in an additional ~70-95kg N/ha being available for the succeeding crop (using an estimate of 20kg of N being fixed for each tonne of dry matter produced (Peoples et al 2012)). The trade off in drier years of choosing a later termination timing is there could be less moisture available for the subsequent crop however taking into consideration the wet summer so far of 23/24 this is unlikely to have an impact in this trial.  

Gibberellic acid (GA) had no yield benefit for grazing or hay production. 

GA is a hormone that is naturally produced by plants in warmer weather and promotes cell elongation. It is used in intensive grazing systems to promote grass pasture growth over winter (Matthew et al. 2010). Some anecdotal evidence suggests that there are benefits of applying GA to vetch crops, but there is limited research that supports it. Results from the two BCG trials show that GA applied four weeks prior to the grazing cut had no significant effect on biomass at the grazing time. At both sites, GA applied four weeks prior to the grazing cut had no significant effect on biomass at the grazing time.  

Consistent with the grazing cuts, applying GA did not influence hay yield. There was a large yield penalty in the hay treatments that had been grazed earlier in the season at both sites. Additionally, Volga had the largest increase in biomass after grazing at both sites with the lowest loss of 0.96t DM/ha when considering the combination of biomass removed at grazing and the hay cut (data not shown).   

The application of GA can create large visual differences in vetch paddocks. However, these differences were not reflected in biomass yield measurements. In 2023, there was no yield benefit from applying GA in mid-winter for grazing or for the succeeding hay cut. Previous research at BCG investigating the impact of GA on vetch did not observe differences in hay yield, a delay in flowering or a change in plant height that could indicate better harvestability (Bennett 2020). Trials carried out in SA have shown small increases in grazing and hay yield, although the results are not consistent across seasons and locations (Anderson and Allen 2021). In 2023, the vetch hay generated the largest income of the treatments. 

BCG’s Season Research Results Compendium 2023 

This information is sourced from BCG’s Season Research Results Compendium and was written by BCG Senior Operations Manager and Research Agronomist, Brooke Bennett. The compendium contains the full results and corresponding graphs from all of BCG’s 2023 trials, and is available to members only. You can access the compendium by signing up here to become a member. 

The Project  

This vetch agronomy project is funded through the GRDC NGN (National Grower Network) and was developed in response to growers seeking to understand how the nitrogen legacy of a vetch drop varies depending on end use. The trial will continue in 2024 and aims to assess varying vetch end uses, pre-sowing decisions such as variety type, and in-season agronomic management decisions including grazing and the use of gibberellic acid.  

This information will provide growers with an understanding of how these management strategies impact key cropping factors such as biomass production, total nitrogen fixation and nitrogen removal. In addition, the research aims to develop a greater understanding of the hay quality requirements of growers’ key markets, as well as the crop management practices required to produce quality hay and meet market expectations.  

At the completion of the 2024 season, we will be able to determine if any additional yield for subsequent cereal crops have been generated as a result of the 2023 treatments, and if this results in increased income over the two seasons. 

References: 

Anderson D., and Allen R., 2021, 2021 Hart Trial Results, ‘Improving Vetch Dry Matter Production’ pp 52-58. https://www.hartfieldsite.org.au/media/2021%20TRIAL%20RESULTS/2021_Hart_Trial_Results_Improving_vetch_dry_matter_production.pdf    

Bennett B., 2020, 2020 BCG Season Research Results, ‘The effects of gibberellic acid on biomass and harvestability of vetch hay’ pp 115-119. https://www.bcg.org.au/research-article/the-effects-of-gibberellic-acid-on-biomass-and-harvestability-of-vetch-hay/    

Peoples MB, Brockwell J, Hunt JR, Swan AD, Watson L, Hayes RC, Li GD, Hackney B, Nuttall JG, Davies SL, Fillery IRP 2012, Crop and Pasture Science 63 ‘Factors affecting the potential contributions of N2 fixation by legumes in Australian pasture systems’ pp. 759-786   

Matthew C., Hofmann WA., and Osborne MA 2009, New Zealand Journal of Agricultural Research, ‘Pasture Response to Gibberellins: A Review and Recommendations’ pp 213-225. 

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