- Crop sequences are most profitable when break crops are grown in order to solve agronomic problems in continuous cereals (grass weeds, root disease, low soil N).
- Despite sometimes being less profitable than continuous wheat in the year in which break crops were grown, trial work has demonstrated that crop sequences involving a broadleaf break crop can be more profitable than continuous wheat.
- Standing stubble improves the micro-climate for lentils and increases yield, regardless of seasonal conditions.
A break crop is one sown to provide diversity to the cropping rotation.
In the Wimmera and Mallee, legume and oilseed crops and pastures are considered break crops in a traditionally cereal dominant cropping system.
Broadleaf break crops can be perceived to be of higher risk than cereals in medium to low rainfall environments due to lower water use efficiency and poor profitability in drought years. However, in recent times, profitability has varied with high value break crops.
Break crops increase flexibility in the management of weeds, diseases and nutrition.
Despite sometimes being less profitable than continuous wheat in the year in which break crops were grown, trial work has demonstrated that crop sequences involving a broadleaf break crop can be more profitable than continuous wheat.
GRDC water use efficiency break crop trial (2009-2012)
An experiment was established in 2009 to identify low risk, profitable break crops and end-uses (grain, hay, brown manuring) and quantify their benefits to subsequent wheat crops. At a site near Hopetoun in the Mallee region of north west Victoria on two soil types (clay and sand), three different broad-leaf break crops, wheat and long-fallow were grown in 2009 or 2010 and followed by wheat in 2010 and 2011.
Wheat grown after juncea canola, peas and vetch (sand soil) and vetch and peas (clay soil) yielded more than continuous wheat.
At the clay site pea hay in 2009 followed by wheat in 2010 and 2011 had the highest mean gross margin (Figure 1). At the sand site, canola grain, pea hay and vetch hay followed by wheat were more profitable than continuous wheat or fallow followed by wheat (Figure 1).
As reported by BCG in the 2012 Australian Agronomy Conference Paper: Break Crops Pay in the Victorian Mallee, crop sequences are most profitable when break crops are grown in order to solve agronomic problems in continuous cereals (grass weeds, root disease, low soil N). The risk of losing money on break crops can be greatly reduced if growers make their crop selection based on the amount of soil water, nitrogen and timing of the autumn break, and if inputs are kept to a minimum and applied in response to favourable conditions, such as in-season top-dressing and fungicides, and end-use selection based on seasonal conditions (e.g. cut for hay in a poor season).
Grass-free canola, mustard, chickpeas, field peas, vetch medic pasture and fallow can result in significant reductions in the inoculum in a cropping sequence but the rotation benefits last for only one crop season.
Non-cereal crops can be infected by rhizoctonia however, most do not allow the build up of inoculum. Grass free canola and medic pastures reduce rhizoctonia inoculum levels resulting in increases is subsequent cereal yield. Other legumes such as field peas, chickpeas, and vetch also showed limited or no inoculum build-up. Importantly, the effect of rotations generally lasted for one crop season only. (ref: Management of soil-borne rhizoctonia disease risk in cropping systems and How crop rotation and summer rainfall influence rhizoctonia).
Results from trials undertaken at Chinkapook in the Victorian Mallee, when sub-soil water was present 2011-2014, growing high value canola and legume break crops was profitable in the Mallee.
Where brome grass populations were high, break crop sequences of longer than two years were necessary to decrease numbers and keep them down. (Source: BCG 2014 Season Research Results, Weed Management, Crop sequences and brome grass, page 119).
Standing stubble improves the microclimate for lentils and increases yield, regardless of seasonal conditions.
Research results showed a greater yield advantage could be achieved from standing stubble rather than slashed stubble, especially when lentils are sown later.
Sowing lentils into standing stubble may provide further benefits to harvestability e.g. increased biomass, better plant and pod height and less lodging.
Further information: Pulse Australia update 2014
BCG Farming Systems site 1999-2013
The BCG farming systems site was established in 1999 in response to conjecture from Wimmera and Mallee farmers about which farming system was most profitable, productive and sustainable. This systems trial existed for 14 years (1999-2013) and examined the following farming systems:
- A ‘Fuel Burner’ system which featured mainly cereals, the regular use of tilled fallow (commenced prior to harvest), low intensity livestock and full disturbance tillage at sowing
- A ‘Hungry Sheep’ system which featured intensive cropping (mainly cereals), intensive grazing, winter lambing, grazing over summer to take advantage of stubbles and to control weeds, early sown cereal/pasture forage for feed and generally full disturbance tillage at sowing
- A ‘No-Till’ system which featured minimum soil disturbance seeding (knife points, press wheels, 30.5cm row spacings) and no livestock. Initially this system included the high use of break crops but later cereals were predominant and some chemical fallow
- A ‘Reduced-Till’ system which took a flexible approach – tillage or full disturbance sowing, mainly chemical weed control, a mix of cereals, canola and other break crops and, in early years, some livestock over summer
The analysis conducted on the farming system trial since 2000 demonstrated that no one system is more profitable than any other (2012 BCG Season Research Results pp. 176). The research highlighted that it doesn’t matter which system you employ, provided you manage that system well.
The severe subsoil limitations discovered within the highly alkaline calcarosol soils at the site drove home understandings about the inability of such soils to support pulse and canola crops, particularly in dry seasons. The hard lessons learned by the ‘No-Till’ system which suffered failed canola and pulse crops in the early years helped growers appreciate both the challenges of subsoil constraints and the value of a chemical fallow. Once the ‘No-Till’ rotation was altered to a continuous cereal with chemical fallow it’s performance results improved markedly, in 2005 growing the highest yielding wheat crop at the site (on a chemical fallow). Read more about the BCG Systems Site here.
Break crop residue over summer is generally less than that of cereal stubbles in the Wimmera and Mallee. Less groundcover therefore remains to protect the soil, particularly sandy soils from wind erosion.
Less stubble from break crops, how ever, may enable greater herbicide efficacy for pre-emergent herbicides that are readily stubble bound.
The challenge is to choose the right break crop in the right sequence in the right conditions.
Continued research being carried out through the stubble project will be extended by BCG over the next three years and will hopefully address these challenges and opportunities.
This research is being conducted by BCG as part of the GRDC Maintaining profitable farming systems with retained stubble initiative (project BWD00024 Maintaining profitable farming systems with retained stubble in Victoria and Tasmania).