3.3. Spatiotemporal patterns of soil water use
Soil water use by jujube trees was calculated based on the daily soil
water data (Figure S4) acquired using the EC 5 sensors. The depth
density of water uptake (DWU) under the four plots in the three
different years is shown in Figure 5. The DWU generally decreased
exponentially with soil depth, matching the FRLD distribution (Figure
3), and the values approached zero below a depth of 100 cm. The normal
year of 2014 generally had higher DWU values than the two drought years
in the top , with the exception of the MST plot where values were very
similar for the three years. On the other hand, the drought years of
2015 and 2016 had clearly higher DWU values than the normal year 2014.
/Figure 5/
The proportion of soil water use (PWU) relative to the entire profile
(0) is presented in Figure 6, for the shallow layer (0) and three
different deep layers (100-160, 160-220 and 220). Overall, the shallow
layer was responsible for the majority of water uptake in the profile
and the PWU of this layer was generally higher than 63%, irrespective
of plot and year. Significant annual variations in PWU were observed
under all plots. In the normal year, the PWU values for the shallow
layer ranged from 77.5% to 87.7%, and decreased by 15.6±5.3% and
15.9±7.9% (relative ratio; mean ± one standard deviation) in the
drought years of 2015 and 2016, respectively. In contrast, the PWUs in
the deep layers dramatically increased in both drought years compared
with the normal year. In the serious drought year, the PWUs increased by
78.3±73.6%, 124.7±36.9%, and 127.1±74.8% (relative ratio; mean ± one
standard deviation) in the 100-160, 160-220, and 220 layers,
respectively. In the moderate drought year, even higher relative ratios
were observed in the JBT plot.
/Figure 6/