By De-Anne Ferrier (BCG), Laura Goward and Mark Peoples (CSIRO)
- When vetch is established in March and is terminated ‘early’ (three to four months later, in June, July), soil water will be conserved for the subsequent wheat crop; the risk of haying off due to high nitrogen will be lower than if the vetch were terminated ‘later’ (August, September).
- Vetch biomass production of approximately 2t/ha is unlikely to cause a subsequent heat crop to hay off given dry seasonal conditions.
- Residual nitrogen from vetch brown manure can carry over for two years and influence cereal crop growth, but the conservation of soil water is more critical in seasons of Decile 2 or lower.
Terminating vetch at the optimum time to achieve the greatest benefit for consecutive wheat crops has been the focus of a three year BCG study funded through GRDC’s ‘Facilitating increased on-farm adoption of broadleaf species in crop sequences to improve grain production and profitability’ initiative.
Finding the balance between early vetch termination to maximise soil water conservation,
and later termination for greater biomass and nitrogen (N) production to benefit the next crop, can be difficult given the variable climate.
In the vetch establishment year (2012) of this project, between 3-5t/ha of biomass production was measured in the later termination treatments (BCG 2012 Season Research Results, pp. 49). In 2013, summer and growing season rainfall were Decile 1 and 2 respectively and wheat which established on later vetch terminations, hayed off (BCG 2013 Season Research Results, pp. 119).
The value of vetch termination and its influence on soil water, nitrogen and
profitability on subsequent wheat crops was the focus of this study.
The research showed that early vetch termination is lower risk, particularly in a Mallee environment where soil water is often limited and haying off can occur if too much mineral nitrogen is taken up by the subsequent crop and a dry finish occurs.
In dry seasons, residual mineral nitrogen from vetch brown manure can influence cereal crop growth in the following two years. However, this trial demonstrates that soil water is more critical than nitrogen in Decile 1 and 2 rainfall years.