*3.5. Water Use E*ffi*ciency (WUE)*

The relationship between WUE for canola total biomass and grain yield was significant. The correlation of both WUE values was also determined (Figure 4). The effects of different WTD levels on both the grain yield and total biomass WUEs were also significant. The highest grain yield and biomass WUE values for T90 were 0.0126 and 0.0449 g lys−<sup>1</sup> mm<sup>−</sup>1, respectively. The lowest WUE values for both parameters occurred with the T30 treatment (Table 5).

After cutting the 16 lysimeters as mentioned earlier, each soil profile was divided into three different layers: 0–30, 30–60, and 60–90 cm (measured from the top) to determine the percentage of the root mass distribution in terms of WTD (Table 6). Overall, the highest root–mass ratio was found with plants in Tcontrol at the 0–30 cm soil layer (4.52 g and 54.6%). There was an inverse relationship between soil depth and root mass distribution for Tcontrol plants. When WTD changed from 90 to 30 cm, the root weight increased from 0.73 to 4.52 g. Since Tcontrol did not have WTD, a lower amount of roots was found in deeper soil layers. Significant differences were observed in 0–30 cm between T90 and other treatments, and a greater root mass was observed at 60–90 cm in treatment T90. The highest average root weight was 7.97 g in the third layer for plants in the T90 treatment (Table 6). Similar to the inverse relationship between the soil depth and root mass for Tcontrol, an inverse correlation was observed between WTD and the root mass for T90.

**Figure 4.** Canola water use efficiency with treatments: (**a**) grain yield water use efficiency (WUE) and (**b**) total biomass WUE.

**Table 5.** Statistical analysis results of the canola's mean grain yield, total biomass, water use, and water use efficiency.


Note: Lowercase letters; a, b, c, and <sup>d</sup> show statistical significance at *p* = 0.05. The values followed by the same letter in each column are not significantly different.

**Table 6.** Average root mass and proportions of roots.


Note: Lowercase letters; a, b, c, and <sup>d</sup> show statistical significance at *p* = 0.05. The values followed by the same letter in each column are not significantly different.
