Forage canola (Brassica napus): spring-sown winter canola for biennial dual-purpose use in the high-rainfall zone of southern Australia

Abstract

European winter canola (Brassica napus L.) varieties adapted to the long, cool seasons in high-rainfall areas of southern Australia have recently been adopted as autumn-sown, grain-only and dual-purpose crops. A spring-sown winter canola could be used as a biennial dual-purpose crop, to provide additional forage for summer and autumn grazing before recovery to produce an oilseed crop. We report a series of field experiments demonstrating that European winter canola types have suitable phenological characteristics to allow for their use as biennial, spring-sown crops, providing significant forage (2.5–4 t ha–1) for grazing while remaining vegetative through summer and autumn, and recovering following vernalisation in winter to produce high seed yield (2.5–5.0 t ha–1). Sowing too early (September) in colder inland areas risked exposure of the crop to vernalising temperatures, causing the crop to bolt to flower in summer, whereas all crops sown from mid-October remained vegetative through summer. Crop stands thinned by 20–30% during summer, and this was exacerbated by grazing, but surviving stands of ~30 plants m–2 were sufficient to support high yields. Grazing had no effect on grain yield at one site, but reduced yield by 0.5 t ha–1 at a second site, although this was more than offset by the value of the grazed forage. The spring-sowing approach has potential to replace the existing forage rape–spring cereal sequence, or to add a further option to the existing autumn-sown winter canola in areas such as southern Victoria, where early autumn establishment can be problematic and spring-sown crops can better withstand pests and winter waterlogging, which limit yield of autumn-sown crops. Because these are the first known studies in Australia to investigate the use of spring-sown winter canola, further work is warranted to refine further the crop and grazing strategies to maximise productivity and profitability from this option.