Productivity of diverse forage brassica genotypes exceeds that of oats across multiple environments within Australia’s mixed farming zone

Abstract

In many areas of Australia’s mixed farming zone, cropping rotations are dominated by cereals and some areas have few suitable broadleaf alternatives. Forage brassicas are widely used in high rainfall livestock systems, but this study shows that several genotypes offer an alternative to forage oats in drier environments within Australia’s mixed farming zone. We compared a diverse set of forage brassica genotypes sown in autumn and winter with benchmark species, principally oats, across 10 experimental site-years. In both early (800–1300 growing degree days after sowing) and late (1600–2100 growing degree days after sowing) grazing windows, several forage brassica genotypes had forage production similar or superior to oats and dual-purpose canola. Many forage brassica genotypes produced higher yields of metabolisable energy (ME) and crude protein (CP), particularly in the late grazing window. In the early grazing window, Rival and Green globe turnips and HT-R24 forage rape consistently produced ~15% above the site mean for all productivity measures, whereas kale produced ~40% less than the site mean. In the late grazing window, oats produced the greatest amount of edible biomass (~44% higher than the site mean); however, Goliath and HT-R24 forage rapes, Pallaton raphanobrassica and dual-purpose canola had the highest yields of ME and CP (~16% higher than the site mean). Green globe turnip, Hunter leafy turnip and Regal kale produced ~22% less than the site mean in this late grazing window. Multi-environment analyses revealed no genotype × environment interactions within the early grazing window. In the late grazing window, there were several genotypic adaptations, particularly for Pallaton, which performed better in low–medium production environments than the other genotypes. We show that forage brassicas offer superior yields of ME and CP, indicating that they may be better able to meet the energy and protein demands of grazing livestock than forage oats.