*2.4. Calculation of Crop Water Use from Groundwater and Irrigation Water*

After plant harvest, four randomly selected lysimeters from each treatment were cut vertically to determine the canola plant root's dry mass. In order to analyze the entire root distribution in each treatment, lysimeters were cut from the top through the bottom using electric saw. During the soil extraction process, three plant root depth intervals (0–30, 30–60, and 60–90 cm) were selected based on three water table depths. The soil in the lysimeters was washed, and the roots were separated gently from the soil. The roots were air-dried for 24 h before weighing to determine the root distribution and dry mass at each depth interval. Evapotranspiration in each lysimeter was calculated using Equation (1):

$$(\Delta \mathbf{S}) = (\mathbf{I} + \mathbf{C}\mathbf{r}) - (\mathbf{D}\mathbf{p} + \mathbf{E}\mathbf{T}) \tag{1}$$

where Cr is the water inflow due to capillarity, I is the irrigation, Dp is the deep percolation, ET is the evapotranspiration, and ΔS is the change in soil water content. Precipitation, runoff, and deep percolation were not applicable in this study since the experiments was performed in a controlled greenhouse. Irrigation was only applied to the control experiments. After evaluation of the controlled environment's conditions, the soil water balance equation was used to determine ET for each treatment (Equation (2)):

$$\text{ET} = \text{Cr} + \text{S}\_1 - \text{S}\_2 \tag{2}$$

where S1 is the initial soil water storage (soil moisture) and S2 is the final soil water storage in the lysimeters. Water reduction in the Mariotte bottles was measured every 15 days to determine the capillary water inflow in the lysimeters. The amount of water used by the canola was calculated using the soil water balance equation (Equation (1)) [19].

To determine the initial moisture conditions of the lysimeters at the beginning of the experiment, soil water potential sensors were used. After cutting the sixteen lysimeters, soil water content was measured, and the final moisture conditions of the sixteen lysimeters were determined. The soil water release curve was used to consider 50% of the total available moisture as the RAM in the soil profile of control treatment. The irrigation water depths for the lysimeters were calculated by using Equation (3) [20]:

$$\mathbf{d} = \sum\_{i=1}^{n} \frac{\mathbf{F}\_{\rm ci} - \mathbf{M}\_{\rm bi}}{100} \times \mathbf{A}\_{\rm si} \times \mathbf{D}\_{\rm i} \tag{3}$$

where d is the equivalent depth of water in cm, Fci is the field capacity of the soil layer in percent by weight, Mbi is the current water content of the soil layer in percent by weight, Asi is the apparent specific gravity (bulk density), Di is the depth of each soil layer, and n is the total number of soil layers.

To determine the soil water retention curve, the water in each lysimeter was drained out through a valve at the bottom of the lysimeter until 50% readily available soil moisture content was obtained in the lysimeter. For the control treatment, supplemental water was applied at the surface of the lysimeters to maintain the soil field capacity at 0.32 cm3/cm3.

WUE was calculated for both grain yield (harvested seed weight) and total biomass (harvested total dry matter). Since sixteen lysimeters were cut, the grain yield and total biomass values of sixteen lysimeters were used for grain yield and biomass WUE calculations. The same statistical difference in the grain yield and total biomass WUE results of thirty-two lysimeters was extrapolated by using the data of sixteen lysimeters in response to different WTDs.
