Reliability of canola production in different rainfall zones of Western Australia

The area of canola in the wheat-based farming systems of the wheatbelt of Western Australia (WA) expanded rapidly during the 1990s and has subsequently decreased. Due to the short history of canola production in WA, there is little information on yield and oil content expectations in relation to rainfall, location, and soil type. In this paper we: (1) present the recent history of canola production in the context of the long-term climate record; (2) assess the effect of location, rainfall, soil type, and soil water at sowing on yield and oil content; and (3) determine cut-off sowing dates for profitable canola production. Simulations were run using the APSIM-Canola model with long-term climate records for 3 selected locations from the low-, medium-, and high-rainfall zones and different soil types. Analysis of recent trends in canola area showed that poor seasons and price volatility in the last few years have contributed to farmers' perception of risk and hence the decline in area sown. Long-term simulations showed the importance of location, sowing date, soil type, and stored soil water at sowing on grain yield. Yield was negatively related to sowing date. Light-textured soils had lower yields and larger yield penalties with delayed sowing than heavy-textured soils. Soil water at sowing gave a yield advantage in most years in all locations studied, but especially in low- and medium-rainfall locations. Variation in oil content was most strongly affected by sowing date and location, while soil type and soil water at sowing had a minor effect. Long-term simulation analysis can be used as a tool to establish the latest possible sowing date to achieve profitable canola for different locations and soil types, given different canola prices and growing costs. Given the vulnerability of profitability to seasonal conditions, in the low- and medium-rainfall zone, the decision to grow canola should be tactical depending on stored soil water, sowing opportunities, seasonal climate outlook, prices, and costs. In contrast, in the high-rainfall zone, canola production is relatively low risk, and could become a reliable component of rotations.