Crop sequences in modern Australian farming systems

It is widely recognised that cereal crops tend to perform better when grown after a legume or brassica break crop. Indeed, crop rotation, where different crops and/or phases of pastures are rotated to break disease and pest cycles, alter the water balance and nutrient dynamics, or help manage weed seed banks, is one of the oldest agronomic practices used in agriculture. In thisCrop & Pasture Science Special Issue, Angus et al. (2015) discuss how crop rotation was utilised by ancient civilisations to sustain cereal grain production. Consequently, it may be argued that the benefits of break crops and crop rotation should be well understood. However, recent reviews of the biological mechanisms of break crops (e.g. Kirkegaard et al. 2008; Peoples et al. 2009; Kirkegaard and Ryan 2014) suggest that while biological concepts are known, the impact of including a break crop on the yield of the following crop is often variable. Angus et al. (2015) uses a meta-analysis approach to build upon earlier reviews to argue that the size of the break crop effect on cereals is primarily influenced by the type of break, where oats < oilseeds < legume crops. Individual studies measuring the size of the break crop effect have been more equivocal, reporting yield advantages of between 0.6–0.8 t/h