Canola yield and quality under tile drainage in the Canadian Prairies

For areas with seasonally shallow water tables and poorly drained soils, subsurface drainage systems are ideal for removing excess water from the root zone and improving soil workability, trafficability, and timeliness of field operations. With increased interest in tile drainage in southern Manitoba, the objective of this study was to evaluate the impacts of drainage on canola yield and canola oil qualities over three growing seasons (2019-2021) in Winkler, Manitoba. The study was carried out on replicated field plots with three different drainage treatments: controlled drainage (CD), free drainage (FD), and no drainage (ND). Subsurface drain tiles were installed at a depth of 0.9 m. The drains were spaced at 8 m for CD and 15 m for FD. Compared to FD plots (3.02 Mg/ha), the CD plots (3.51 Mg/ha) had significantly higher yields in 2019 with good rainfall. With low rainfall in 2020 and 2021, the impact of drainage, especially CD, diminished, with no significant differences between the treatments. In 2020, the average yields were 3.12, 2.52, and 2.97 Mg/ha for ND, CD, and FD, respectively. Similarly, in 2021, there was no significant difference between CD (1.14 Mg/ha), FD (1.52 Mg/ha), and ND (1.07 Mg/ha). The impact of CD under drought conditions was not significant. This could be related to the narrower drain spacing, which tends to remove water rapidly within the soil profile during short periods of high-intensity rainfall. The canola quality assessments (oil, protein, glucosinolate and fatty acid profile) showed no significant differences between ND, CD, and FD in each of the years. This suggests that environmental variables (mainly temperature and precipitation) may have masked drainage impacts on canola quality.