Management practices that maximise gross margins in Australian canola (Brassica napus L.)

Abstract

Farm gross margins for canola are directly tied to yield, yet growers miss out on ∼40−50% of water-limited potential yields (YW). Many factors including weather variability can limit returns on production expenditure and lead growers to moderate inputs that also limit yield. The purpose of this study was to identify management practices that growers could use most profitably under differing seasonal conditions. Canola crop yields were simulated with APSIM at seven diverse Australian locations in a factorial array of management practices including sowing date, sowing density, cultivar, rate of cultivar development and nitrogen fertiliser rate. The implication for growers of input costs for the different management combinations was evaluated in terms of the extent that costs were recovered (ratio of gross margins to variable costs) and magnitude of variable input costs for gross margins. A regression-tree data-mining approach was used to identify the most profitable and highest yielding combinations of management practices. Environmental conditions (defined here by combinations of date of sowing and ‘perfect knowledge’ of growing season rainfall) had greatest impact on gross margins and few profitable management practices could be identified unless environmental conditions were first accounted for. When crop management practices were tailored to rainfall and sowing date to maximize gross margins, yields were up to 2 Mg ha−1 greater than the average yield achieved by industry. Yield generally increased in response to increasing variable costs but gross margins tended to plateau; after this point higher variable input costs were matched but not exceeded by revenue from increased yield. Gross margins changed in response to individual management factors: for sowing date, gross margins decreased with progressively later sowings from mid-March. For N fertiliser rate in all sowing dates, it was more profitable to use higher N fertiliser rates for higher rainfall deciles, and to use lower N rates as sowing was delayed. Cultivars with slow to medium rates of development were most profitable for early sowings up to the end of April, except where rainfall was low (in low rainfall deciles or for locations in low rainfall zones). Hybrid and conventional open-pollinated cultivars had similar gross margins, which were greater than for the Triazine-tolerant open pollinated cultivar due to its lower yield potential. Selection of most profitable practices was enhanced with knowledge of seasonal rainfall, but time of sowing matched with rate of development and a non-TT-OP cultivar could be selected to maximise gross margins without knowledge of rainfall. Nevertheless, high costs of production may hinder the most profitable selection of management practices.