Dilnee Suraweera1, Malcolm McCaskill1, Penny Riffkin1, Debra Partington1, Jamie Smith1, Irma Grimmer1, and Tony Dickson1
1 Agriculture Victoria Research, 915 Mt Napier Rd, Hamilton Victoria 3300, Australia
Yield potential of canola in the high rainfall zone in the south-west Victoria is higher than most other parts of Australia due to higher rainfall and longer growing season. However, in some years it is constrained by waterlogging during winter and early spring. Adequate phosphorus (P) fertiliser at sowing is critical in achieving high canola yields. Data were collected in 2017 growing season from canola field plots affected by waterlogging in an experiment conducted with a range of soil P fertility levels at the Long-term Phosphate Experiment (LTPE) site in Hamilton, Victoria. The aim of this study was to examine the canola yield responses to additional P fertilizer at sowing under different waterlogging regimes. A scale was developed to assess the severity of waterlogging at the start of flowering (GS 4.1) and full flowering (GS 4.9) stages. At grain maturity, plants were harvested separately based on the scale. Grain yield, grain number, non-grain biomass, 1000-grain weight and harvest index were determined. In 2017, the growing season rainfall was greater than the long-term average particularly over August-September resulting in significant waterlogging over this period which coincides with the canola bud visible and flowering stages. Response relationship showed that canola grain yield significantly increased (R2= 0.84, p<0.001), in response to P fertilizer application at sowing. This response to P was greatest for non-waterlogged plants and was progressively lower as the magnitude of waterlogging increased. Waterlogged plots reduced canola grain yield by 38-62% compared to non-waterlogged plots under the range of applied P fertilizer rates. There was a significant interaction between P fertilization and waterlogging in most of the parameters measured. Therefore, enhanced P fertilization at sowing with non-limiting levels of other nutrients has potential to increase canola grain yield under waterlogged conditions. But the response of canola grain yield to P fertilizer at sowing is reduced with increasing waterlogging severities. These findings will be useful to understand the P fertilizer requirements for canola growing in waterlogging-prone soils.