Influence of water application levels and plant densities on the plasticity of canola in the central Free State, South Africa

In South Africa canola (Brassica napus L.) is cultivated in rotation with wheat under winter rainfall in the Western Cape Province. Expansion of the crop to the other eight provinces is advocated to reduce a shortage of locally produced plant oils. Moreover, canola can serve as a rotational crop for wheat in the summer rainfall provinces. In the central Free State, agronomic information for canola production is lacking. An experiment with a line source sprinkler irrigation system was conducted to establish the influence of water application levels (175, 233, 295, 351 and 420 mm) in combination with plant densities (25, 50, 75, 100 and 125 plants m(-2)) on yield responses, yield components and growth parameters of canola. Seed (653-4653 kg ha(-1)) and stover (1983-6733 kg ha(-1)) yields induced by the treatment combinations proved that canola has a high level of plasticity. Over the full range of water application levels, highest seed and biomass yields were realised at densities of 25 and 75 plants m(-2), respectively. The compensation of yields at lower plant densities was due to the production of more branches, pods and seeds per plant. Under full irrigation, densities of 25 and 75 plants m(-2) are optimal for seed and biomass production, respectively.