## 3 Results
### Water Requirements of Japanese Plum Orchards  
The water requirements of an orchard vary throughout the course of a season, depending on the phenological growth stage and throughout an orchard's life span depending on its age and canopy cover [40]. Stone fruits are characterized by four phenological growth stages, namely (i) stage I: the first rapid fruit growth; (ii) stage II: pit hardening; (iii) stage III: the second rapid growth and (iv) stage IV: post-harvest [62]. Vegetative growth (the growth of leaves, stems and roots) mainly occurs during stages I and II, when plant vigor can be manipulated to control fruit size and quality. Fruit growth occurs exponentially during the first stage (stage I), typically lasting 30 days or less. This exponential growth is succeeded by a lag growth phase, during which the pit (stone) hardens and embryo development occurs (stage II). Stage III is characterized by a second period of rapid fruit growth where the fruit can double in size (up to 40-60%) [9; 62]. By the end of stage III, the fruit is mature and ready to be harvested. Each phase's duration and susceptibility to water stress differ for different stone fruit varieties (i.e., plums, peaches, apricots and nectarines) and cultivars, with early-season plum cultivars typically experiencing a shorter stage II growth phase [63]. In early-season cultivars, fruit growth will continue into the pit hardening phase (stage II), albeit at a slower rate, making it difficult to distinguish between the two stages [63]. In late-season cultivars, the pit hardening phase is longer, and the degree of fruit growth during this stage is minimal. Generally, peak water consumption is experienced during stage III when the second rapid fruit growth occurs, and the fruit cells begin to fill with water and sugar. After harvest, tree transpiration rates gradually begin to decline, resulting from reduced photosynthesis rates, associated with the onset of leaf senescence and a reduction in leaf area as the tree enters a winter dormancy period. Trees are more susceptible to water stress during stages I and III, so accurate irrigation scheduling is crucial to achieve an economically viable yield. The water requirements and evapotranspiration data collated from the literature ranged between 331 and 1211 mm and are summarized in Table 1. A distinction was made between the water requirements during the growing season and throughout the year. The growing season is the period from bud-break (typically in early spring) to harvest. Full-year crop water requirements encompass the water requirements during the growing season along with the supplementary requirements before the beginning of the growing season and post-harvest. Irrigation during these periods, although at reduced rates, is essential for maintaining tree health and minimizing alternate bearing. As such, it should be considered when determining the total water requirement of an orchard, as well as water allocation. The full-year water requirements ranged between 835 and 1211 mm a\({}^{-1}\) when considering figures from orchards under regulated deficit irrigation (RDI) regimes. When these were omitted, i.e., only the control orchards (irrigated at 100% crop water requirements) were considered, the water use ranged between 921 and 1211 mm a\({}^{-1}\). The water requirements during the growing season ranged between 331 and 864 mm. The three cultivars had tolerance to moderate stress with varying response times to drought stress. Regardless of the method used, the rainfall volumes received in the studied period did not cover the water requirements of the fruit trees. The Treder method seemed to be the simplest and most accessible method. Deficit irrigation could be a sustainable novel solution to improve the fruit quality of the cv. African Rose grown under semi-arid conditions. Deficit irrigation treatments were found to be effective at controlling tree vigor, with a lower trunk cross-sectional area growth and pruned wood weight.