## 3 Results
### Evaportranspiration in Plum Orchards
VPD, defined as the difference between the amount of moisture in the air and how much moisture the air can hold, is positively correlated with transpiration [40]. A combination of factors, which vary from crop to crop, influence the water usage within an orchard. These include the type and variety of crop, crop height, canopy structure and density and leaf area [36]. As such, different types of crops and potentially different cultivars will consume varying amounts of water under the same climatic conditions. Each crop type follows a set of phenological growth stages throughout the season, with each growth stage differing in terms of its water consumption. In the case of deciduous fruit trees, characterized by the seasonal growing and shedding of their leaves, orchard water use is typically lowest during the early and latter stages, with peak water use achieved midway through the season. Canopy size (aggregate area of vegetative growth) and canopy structure (spatial arrangement of a plant canopy) are regarded as the most critical factors influencing orchard water use throughout a season and the life span of an orchard [39]. The leaf area index (LAI) is commonly used to understand and compare the canopies of different trees better. [PERSON] et al. [2] investigated the influence of canopy cover and crop load on the seasonal water use of mature, full-bearing and young non-bearing orchards in two major apple production regions in the Western Cape (South Africa). The study concluded that canopy cover, as opposed to crop load, was the main driver of orchard water use in mature full-bearing orchards. Similarly, [PERSON] and [PERSON] [14] reported no statistical significance between different crop loads (medium and low) and the irrigation requirements in a 7-year-old Japanese plum orchard planted with the cv. Black Gold. The movement of water from the soil through plants and into the atmosphere (the Soil-Plant-Atmosphere Continuum) is regulated by the resistive forces within the plant. These include the resistance at the soil-root interface, the roots' endodermic resistance, xylem resistance and the leaf's hydraulic resistance at the leaf-atmosphere interface [41]. The collective influence of these resistive forces and the stomatal conductance regulates the photosynthetic rate of a plant and consequently its transpiration [42]. The management practices employed in an orchard greatly influence water use. These include but are not limited to the use of netting or windbreakers, the chosen irrigation system (i.e., drip or microjet irrigation), the presence or absence of crop cover, its variety and the chosen planting system. The contribution of cover crops to total ET, particularly in apple orchards, has been well documented in the Western Cape. [PERSON] et al. [43] found that orchard floor evaporation (crop cover + soil evaporation) accounted for as much as 80% of the measured ET in young apple orchards with dense crop cover. This value was significantly lower in mature orchards (fractional canopy cover >55%), where the orchard floor evaporation contributed to less than 30% of the measured ET. [PERSON] et al. [2] obtained similar results, where floor evaporation accounted for 18 to 36% of the total ET in mature full-bearing orchards and over 60% in young non-bearing orchards. Both studies concluded that orchard water use could be reduced by decreasing floor evaporation rates. The planting system, which includes the tree planting arrangement, row orientation and the selected training system, and pruning and thinning practices influence orchards' ET by controlling the amount of solar radiation that can intercepted by the canopy [44]. Since photosynthesis is partly limited by light availability, modern-day training systems and pruning techniques aim to enhance light penetration through the canopy, maximizing photosynthesis and fruit production. [PERSON] et al. [45] investigated the effect of different training systems (Lincoln, Vase, Palmette and Tatura trellis systems) on the water use of a plum orchard planted with the cvs.