Agronomic management combining early-sowing on establishment opportunities, cultivar options and adequate nitrogen is critical for canola (Brassica napus) productivity and profit in low-rainfall environments

Abstract

Sustaining diverse, yet productive crop sequences that integrate break crops such as canola (Brassica napus L.) remains a critical challenge for farming systems in low-rainfall cropping environments. Recent advances in canola productivity through early sowing, understanding of critical stress periods, hybrid cultivars and improved nitrogen (N) fertilisation offer promise under many conditions but require careful adaptation for risky, low-rainfall environments. A series of eight experiments was implemented over four growing seasons (2015–18) in the low-rainfall environments of southern Australia to test combinations of sowing date, cultivar selection and N-management strategies. Simulation modelling extended the field experiment results, enabling a simple, whole-farm profit–risk analysis across growing season deciles. The aim was to identify combinations of practices where the potential production and risk were understood, thereby assisting management decisions in low-rainfall cropping systems. Earlier sowing (April) was generally beneficial but only where seasonal conditions led to successful establishment, meaning that the best fit for canola in low-rainfall environments is as an opportunity crop. A hybrid cultivar (triazine tolerant) did not provide a yield advantage in an early experiment, but productivity increases were measured with a modern hybrid cultivar (Clearfield) in a later experiment. Profit-risk analysis suggested that a yield advantage of >20% over open-pollinated cultivars needs to be sustained across the full range of season deciles to generate economic advantage. Although there was relative insensitivity to the timing of N application, an adequate dose of N, either through fertiliser or legume crops, was critical to improve canola productivity. We conclude that opportunities exist to make significant gains in yield (by up to 110% compared with current standard practice) and profit–risk outcomes (~30% increased gross margins across all season types) for canola in low-rainfall environments by using a package of agronomic management decisions that includes early sowing on genuine establishment opportunities, hybrids that offer sustained yield benefits, and matching N dose from both fertiliser and legume crops to yield potential of the soil type and seasonal outlook.