Investigating double break (or stacked rotation) options

In Western Australia, break crop options are currently limited and there is a high proportion of wheat and barley grown in rotation. Cereal crops account for 60-70% of paddocks sown in any one year, with the remaining area sown to a range of crop and pasture types including canola, lupin, clover, volunteer pasture, or left as fallow. In addition, there is an interest in chickpea and lentil to add a high value legume to the crop rotation. The application of these break crops is dependent on the grain price per tonne and on the level of severity of biological constraints present that lead to a reduction in grain yield and which varies from paddock to paddock. The use of a single break crop in rotation has been shown to be an effective tool in managing both weed and diseases that affect wheat production to remove biological constraints to crop production and allow the sustained production of cereal crops. However, with a change in resistance status of many common weeds and diseases, and a change in soilborne pathogens, a single break crop applied to a cropping system that is largely based on cereals has limited effect in reducing the biological constraints, with the longevity of the break crop benefit being reduced. Recent studies into the break crop benefits for highly herbicide resistant weed populations has found that a break of at least two years was needed to prevent grass seed set and substantially reduce grass seedbank numbers.Considering the high percentage of cereal crops grown in Western Australia, there is the need to evaluate the use of double break crop sequences to improve wheat grain yield and profitability. In particular, the Eastern Wheatbelt region has very limited break crop options, and there is the need to investigate the better use of tools such as fallow periods to improve break crop outcomes.