Integrating dual-purpose wheat and canola into high-rainfall livestock systems in south-eastern Australia. 1. Crop forage and grain yield

摘要

The development of guidelines for successful dual-purpose (graze and grain) use of wheat and canola in Australia's high-rainfall zones (HRZ) has mostly emerged from separate wheat-and canola-focused research. Less attention has been placed on the benefits of integrating dual-purpose wheat and canola into pasture-based grazing enterprises. We conducted a farming systems experiment during 2010-11 to evaluate the benefits of integrating wheat and canola as dual-purpose crops into a pasture-based grazing system in Australia's south-eastern tablelands. We compared forage production and grain yield in three separate crop-livestock systems in which the sheep grazed long-season wheat, winter canola or a combination of these. Initial growth rates were higher in early-autumn-sown canola than wheat in 2010, but were much lower although similar in both crops in 2011. Significant forage was available from both canola (3.1-3.4 t ha(-1)) and wheat (2.3-2.4 t ha(-1)) at the onset of grazing, but winter growth rates of wheat were higher than those of canola, leading to increased sheep grazing days (SGD). In the favourable 2010 season, dual-purpose wheat and canola separately provided 2393 and 2095 SGD ha(-1), and yielded 5.0 and 1.9 t ha(-1) grain, respectively, with an apparent nitrogen limitation in canola. In the drier season of 2011, grazing was reduced to 1455 and 735 SGD ha(-1) in wheat and canola, respectively. Wheat yield was reduced from 5.9 to 5.4 t ha(-1) grain by grazing, whereas canola yield was unaffected (3.6 t ha(-1)). In both years, grazing did not affect harvest index or oil content of canola, but harvest index was higher in grazed wheat crops. The yield of wheat and canola crops grazed in sequence did not differ from yield in treatments where animals grazed only a single crop, but the total overall grazing window whencrops were grazed sequentially increased by 1054 and 618 SGD ha(-1) in wheat, and by 1352 and 1338 SGD ha(-1) in canola in 2010 and 2011, respectively. The major benefits of including crops that can be grazed sequentially were the widening of the grazing window and other operational windows (sowing, harvest), along with the rotational benefits for wheat by including canola in the system. Additional benefits to pastures may include eliminating the need to re-sow, because a more productive pasture composition is maintained under lower grazing pressure while stock are on crops, and reduced weed invasion. The commercial availability of new, herbicide-tolerant winter canola varieties provides significant opportunities to underpin the performance of dual-purpose crop sequences on mixed farms in the high-rainfall zone.