Exploring opportunities for dual-purpose canola in south– eastern Australia using crop simulation models

The Agricultural Production SIMulation canola model (APSIM-canola) was calibrated using observations from grazed and un-grazed treatments in order to explore various scenarios for dual-purpose canola in medium rainfall cropping areas such as Wagga Wagga NSW. The existing parameters for APSIM-canola failed to accurately predict the observed growth and grain yield of current cultivars, but adjustments made to the model parameters for new cultivars improved the simulations. For grazed crops, APSIM-canola accurately simulated biomass at flowering. A target biomass at flowering (~5000 kg/ha) has previously been proposed to avoid potential yield loss in grazed crops. The target biomass was confirmed by simulations relating yield to flowering biomass derived using a combination of sowing dates and plant densities. Using rule-based sowing and grazing management strategies our simulations predicted that sowing was possible prior to the 15 th May in 54% of years at Wagga Wagga, while grazing was possible in 53% of years with 50% of those years providing grazing opportunities prior to June 7. Depending on stocking rate, crops could be grazed until early to mid July providing 400-1000 DSE·days/ha without compromising the target flowering biomass (5000 kg/ha) thus maintaining grain yield potential for the site. We conclude grazing canola is a viable option for mixed farms in the Wagga Wagga region. INTRODUCTION Dual-purpose canola has been successfully demonstrated under seasonal conditions which were adequate for regrowth (Kirkegaard et al., 2008; McCormick, Kirkegaard, & Virgona, 2009). Dual-purpose canola is defined here as crops which can provide useful winter stock grazing without reducing grain yield. The success of dual-purpose canola clearly depends on factors influencing regrowth including post-grazing biomass, length of the recovery period prior to flowering and available resources for regrowth, particularly soil moisture. Dual-purpose cropping is season dependant and will rely on opportunities to sow early combined with favourable conditions for regrowth. The probability of success of dual-purpose canola at specific sites can be investigated using long-term climate data and simulation models validated to local conditions. Simulation models are sensitive to soil, climatic and management factors that will dictate sowing opportunities, early forage production, crop phenology and yield development. The specific impacts of grazing on canola growth and yield have not been explicitly simulated previously. This work investigates the use of the Agricultural Production SIMulation (APSIM) model to identify opportunities for grazing canola in an environment that is somewhat drier than those previously reported (Kirkegaard et al. 2008). APSIM-canola has previously been validated for grain-only canola crops in a range of Australian environments including south west NSW (Robertson & Kirkegaard, 2005), semi-arid subtropics (Robertson & Holland, 2004) and Mediterranean environments in Western Australia (Farre, Robertson, Walton, & Asseng, 2002).