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.