Amos Naor

Studies of canopy structure and water use of apple trees on three rootstocks

Abstract Canopy structure and water use was studied on full size, fruit bearing apple (Malus domestica, Golden delicious variety) orchards on three rootstocks: M9, MM106 and the local Hashabi. Structure was measured by the gap fraction inversion method and crop water use (sap flow) by the heat pulse technique. The results showed that leaf area index (LAI) was not significantly different for each rootstock even though measured leaf area (LA) per tree differed greatly. Results also showed LAI measured destructively differed by less than 1 from the gap fraction inversion measurements. No significant differences in LAI between the two orchards (M9, MM106) were found in either measurement method, indicating good relative accuracy of the gap fraction inversion method. Water use of the M9 orchard was much less than that of MM106 and Hashabi orchards, and measured water use was not well correlated with water application based on a graduated class A pan crop factor for the three orchards. The dwarfing rootstock, M9, had the lowest canopy conductance, and was found to have lower sunlit leaf conductance in the porometer measurements, so it is in a condition of water stress. However, the M9 orchard received enough irrigation, therefore, water stress in M9 orchard was probably not caused by insufficient irrigation, but by high resistance to water transport in the stem or root.

Simulating nectarine tree transpiration and dynamic water storage from responses of leaf conductance to light and sap flow to stem water potential and vapor pressure deficit

For isohydric trees mid-day water uptake is stable and depends on soil water status, reflected in pre-dawn leaf water potential (Ψpd) and mid-day stem water potential (Ψmd), tree hydraulic conductance and a more-or-less constant leaf water potential (Ψl) for much of the day, maintained by the stomata. Stabilization of Ψl can be represented by a linear relationship between canopy resistance (Rc) and vapor pressure deficit (D), and the slope (BD) is proportional to the steady-state water uptake. By analyzing sap flow (SF), meteorological and Ψmd measurements during a series of wetting and drying (D/W) cycles in a nectarine orchard, we found that for the range of Ψmd relevant for irrigated orchards the slope of the relationship of Rc to D, BD is a linear function of Ψmd. Rc was simulated using the above relationships, and its changes in the morning and evening were simulated using a rectangular hyperbolic relationship between leaf conductance and photosynthetic irradiance, fitted to leaf-level measurements. The latter was integrated with one-leaf, two-leaf and integrative radiation models, and the latter gave the best results. Simulated Rc was used in the Penman-Monteith equation to simulate tree transpiration, which was validated by comparing with SF from a separate data set. The model gave accurate estimates of diurnal and daily total tree transpiration for the range of Ψmds used in regular and deficit irrigation. Diurnal changes in tree water content were determined from the difference between simulated transpiration and measured SF. Changes in water content caused a time lag of 90-105 min between transpiration and SF for Ψmd between -0.8 and -1.55 MPa, and water depletion reached 3 l h(-1) before noon. Estimated mean diurnal changes in water content were 5.5 l day(-1) tree(-1) at Ψmd of -0.9 MPa and increased to 12.5 l day(-1) tree(-1) at -1.45 MPa, equivalent to 6.5 and 16.5% of daily tree water use, respectively. Sixteen percent of the dynamic water volume was in the leaves. Inversion of the model shows that Ψmd can be predicted from D and Rc, which may have some importance for irrigation management to maintain target values of Ψmd. That relationship will be explored in future research.

The response of field-grown mango (cv. Keitt) trees to regulated deficit irrigation at three phenological stages

The objective of the current study was to examine the effect of different irrigation levels at different phenological stages on fruit yield, fruit size, vegetative growth, and subsequent season crop yield of mango trees growing in sub-tropical weather conditions. Three independent experiments were conducted in parallel in three phenological stages: main fruit growth (MFG)—from fruit set to pit hardening; final fruit growth (FFG)—from pit hardening up to harvest; and post-harvest (PH)—after harvest until the first meaningful rain. Each experiment was consisted of four irrigation levels that were determined as crop coefficients of Penman–Monteith evapotranspiration. Differential irrigation levels were applied in each phenological stage, where commercial irrigation levels were applied in the rest of the season. Crop yield in the MFG stage was unaffected by the irrigation treatments. The number of fruit in the MFG stage increased slightly with increasing water quantities. Average fruit size in the MFG stage decreased with increasing the number of fruit per tree, indicating that the number of fruit rather than irrigation regime is the main determinant of the final fruit size. The number of fruit per tree in the FFG stage was unaffected by the lowest irrigation treatment; however, the same treatment had the lowest fruit size, significant only in 2013. Post-harvest shoot growth in the FFG stage experiment increased with irrigation level (significant in 2013), indicating that water stress in the FFG stage had a carryover effect. The crop yield in the PH stage increased with increasing irrigation rate in the former season, significant in 2011 and 2013. The higher yields in the high irrigation treatments in the PH stage were associated with larger fruit size. The number of post-harvest vegetative flashes increased with increasing crop coefficient (Kc) in the PH stage in the same season, except for the 2011. Crop yield in the PH stage increased with increasing number of post-harvest vegetative flashes in the former season. The results obtained in the current study indicate that the mango in Israel is sensitive to deficit irrigation in both the FFG in an “ON” season and in the PH stage towards an “ON” season.