Figure 6: Whole tree
transpiration estimated from the sapflow sensors in orchard S10 together
with simulated transpiration expressed in liters per tree and day, and
simulated leaf area index (LAIsim) for 2021 and 2022.
Generally, fruit harvest in the orchards was performed between
17th of August and 30th of October
in a first and second harvest for most varieties. Due to very low apple
quantity, harvest in 2022 occurred in a single harvest between
1st Sep and 15th Nov depending on
variety. Simulated harvest in 2021 occurred on 12thand 18th Sep for S09 and S10 respectively, and a few
days earlier in 2022. The two simulation runs using either the adapted
CLM5 irrigation routine or the irrigation data stream showed no
difference in harvest amounts. In 2021, simulated yield was close to the
observed values while the exceptionally low yield in 2022 was not
captured by the simulations (Table 5). Visual inspection of the phenocam
images showed significantly less flowers on the trees in 2022 compared
to 2021 (data not shown). No extreme weather conditions were observed
during the winter 2021/2022 that could explain the reduced flowering.
Other possible reasons for the low number of flowers and hence low yield
in this year may be related to alternate bearing of the varieties or
other factors (e.g., plant physiology or traits, pest and disease or
certain management practices) that are not included in the model.
Table
5: Observed and simulated apple yield in t ha-1 for
orchards S09 and S10 for 2021 and 2022.