- Faba beans have relatively large seed reserves and are able to establish in cereal stubbles.
- There is evidence that cereal stubbles also act as a deterrent to aphids that have the capacity to infect emerging faba crops with viruses such as bean leaf roll virus.
As defined by the GRDC, “a break crop is any crop sown to provide diversity to help reduce disease, weed and pest levels in a paddock” (Break crop benefits fact sheet, March 2011). In Victorian cropping regions a break crop it is generally accepted as a non-cereal crop.
While break crops grown in dryland systems tend to be regarded as riskier than cereals (from a yield and subsequent profit aspect), irrigation reduces the risk of growing these crops to the point where they can be more profitable than cereals.
In irrigated cropping systems in the Murray Mallee region of Victoria, the two major break crops grown are canola and faba beans. A typical rotation is wheat, barley, faba beans and canola. This rotation provides many agronomic advantages:
- Faba beans can contribute significant amounts of nitrogen (N) into the cropping system prior to the high N requirements of subsequent canola and wheat crops.
- Two years of non-cereals offers the opportunity to control grasses with a range of herbicide groups.
- The rotational sequence produces stubble loads that can be handled relatively easily by the break crops.
However, for Murray Mallee growers wishing to retain their stubble, the inclusion of faba bean and canola crop can present challenges in terms of stubble management.
An obvious difference between canola and faba bean seed is the size. This seed size is indicative of the energy reserves that the seeds have to establish a plant. Therefore canola has relatively small reserves to draw upon during germination.
As irrigated cereal stubbles may be in the region of 8 t/ha and crops are often at narrower row spacing’s than on dryland farms, without some form of stubble management, this presents an inhospitable environment for a germinating canola seed. This is because the stubble intercepts the light and tends to result in ‘leggy’ seedlings that use more energy (seed reserves) to establish a plant which can weaken the crop.
Conversely, a faba bean crop produces less stubble and also breaks down more quickly than a cereal stubble, reducing the negative effect on canola establishment.
From field research trials and farmer experience, ICC is working towards identifying how irrigated farmers can retain stubble without compromising plant establishment.
Establishment of irrigated canola
The best management practice target sowing date is from mid-April to Anzac day. In most seasons, this will require irrigation, either pre-irrigation and sow into moisture or dry sowing and watering up. Having adequate moisture at sowing means that starter fertiliser (DAP or MAP) can be safely put ‘down the tube’ at rates up to 125 kg/ha with little detrimental effect.
If watering up, crusting can prevent establishment. The use of soil ameliorants such as gypsum can be beneficial as well as increasing organic carbon levels and reducing cultivation to improve and preserve soil structure.
If canola is to be established into cereal stubbles, the stubble must be managed to reduce the potential negative effects. Mulching, incorporation and burning all have their place.
Incorporation can be successful, particularly if it is combined with added fertiliser and irrigation a month or so before sowing, but nutrient tie-up can still be an issue.
Mulching can also be a useful management tool as long as the stubble load is not too great as to affect the ability of the sowing implement to accurately place the seed at a shallow sowing depth.
Establishment of irrigated faba beans
Fabas have the ability to handle cereal stubbles reasonably well. The target sowing date is late April to early May and seed should be treated with insecticide to reduce the chance of aphid-borne virus infections.
Fabas can be sown into pre-irrigated or watered up soil, with pre-irrigation giving the advantage of being able to apply a knockdown herbicide prior to sowing allowing faba beans to be sown a little deeper to chase moisture if necessary.
The 2015 ICC research into break crops in retained stubble systems will continue at Kerang. Trials are as follows:
- Legumes in the rotation – a small plot replicated trial aiming to demonstrate the value of legumes (faba beans) in the rotation. Treatments will include wheat sown on wheat, barley, canola and faba bean stubble.
- Establishing canola on cereal stubbles – a small plot replicated trial aiming to accelerate stubble decomposition by adding fertiliser, thus aiding canola establishment. The trial is seeking to find an alternative way to manage stubble without burning it.
- Establishment of canola using soil ameliorants – a small plot replicated trial looking at how various rates of lime and gypsum applied in 2014 influence canola establishment.
This research is being conducted by ICC 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).