Effect of Drought Stress on Water Requirement of Chinaberry (Melia azedarach L.) at Diverse Ages in Two Consecutive Years

Background and Objectives: Water resources are scarce in arid and semi-arid regions, which makes it challenging to allocate them for development of green spaces. This includes public and private green spaces, forests and parks, gardens, and green belts, as water allocation is fiercely competitive with other uses such as agriculture, industry, and even drinking water. In arid areas, using drought-tolerant species is crucial to ensure the sustainability of green spaces.
Materials and Methods: This study aims to investigate the impact of drought stress on water requirement of Chinaberry plants of different ages in the Robatkarim arid region in Tehran province. The study was conducted using a factorial design scheme with the factors of species type, age, and drought stress. The study design was completely randomized, with 10 replications in two consecutive years. The variables included the species factor (Chinaberry) and the age factor at three different levels (one, three, and five years). The drought stress factor was divided into three levels: mild (0.3), intermediate (0.5), and high (0.7) stress levels, resulting in a total of 9 treatments. For each species, 90 microlysimeters were executed, considering the 10 repetitions. The research process includes the phases of determining irrigation planning, monitoring moisture levels in drought stress levels, measuring the water requirements of the species, calculating the reference evapotranspiration, and vegetation coefficient, and evaluating the effects of different drought stress levels on water requirements. The vegetable factor in this research was Chinaberry species. The volume of large, medium, and small microlysimeters was estimated at 0.016, 0.01, and 0.004 m³, respectively.
Results: The amount of water consumption in Chinaberry seedlings in the year 2021 and during the growth period of plant and in different applied treatments was: At drought stress of 0.3 (238.9 mm), 0.5 (282.4 mm) and 0.7 (310.03 mm) at age of 1 year; at drought stress of 0.3 (322 mm), 0.5 (374.8 mm) and 0.7 (421.4 mm) at age of 3 years; and at drought stress of 0.3 (471.7 mm), 0.5 (374.8 mm) and 0.7 (421.4 mm) at  age of 5 years. The amount of water consumption in 2022 for the applied drought stress treatments was equal to 233.14, 276.6 and 301.13 mm; 314, 364 and 394 mm; 471.73, 499.1 and 530.73 mm, respectively. Comparison of the mean values of potential evapotranspiration in the studied Chinaberry seedlings under different stresses shows that their mean is significant with a probability of 0.01 in different groups and during the 2021 and 2022. In general, drought regimes affect the water requirement of Chinaberry at different ages.
Conclusion: It is crucial to consider appropriate drought stress in afforestation plans in arid and semi-arid areas to save water and provide suitable conditions for tree growth and survival.