Figure 5: Effect of irrigation
target soil matric potential (\(\psi_{\text{target}}\)) and irrigation
threshold fraction (\(f_{th\text{res}h}\)) on total irrigation amount
(Irr), irrigation starting date (Irr start), number of irrigation events
(Irr events), irrigation frequency (Irr frequency), irrigation dose per
event (Irr dose), soil moisture (SM) at 5, 20, and 50 cm depth, and
yield. Shown are yearly average values for S09 and the year 2016.
3.1.2 Tree transpiration and fruit harvest
The comparison of measured sapflow with simulated transpiration
expressed as water consumption per tree is presented in Figure 6.
Observed sapflow varied significantly between different trees resulting
in large inter-quartile ranges. The two model runs showed no difference
in simulated tree transpiration despite the difference in irrigation
amount and timing. In 2021, CLM5 showed higher values and a slight shift
in the seasonal dynamic as a result of a too early onset of leaf
development compared to the observed values (LAIsim in
Figure 6). Simulated leaf duration and total transpiration agreed well
with the measurements in 2022. Tree transpiration peaked in July with a
measured monthly average of 12.5 (2021) and 20.2 L
tree-1 day-1 (2022) and simulated
values of 25.1 (2021) and 24.5 L tree-1day-1 (2022). The better agreement between simulated
and observed values in 2022 followed a reinstallation that was performed
after partial sensor failure and unreliable measurements that resulted
in data gaps for the 2021 growing season. The 2021 data should therefore
be handled with care when interpreting absolute values. Simulated
maximum leaf area index (LAI) was reached in early July. Full canopy
cover in the orchards occurred in the second half of June, so slightly
earlier, based on visual inspection of the phenocam pictures (data not
shown). Simulated leaf area and hence transpiration fell to zero by
December, which broadly agreed with observed sapflow and leaf senescence
deduced from the phenocam images.