Evaluation of Growth Parameters for Jatropha curcas L. (Biofuel Plant) under Salinity and Water Stress Using Tensiometer for Irrigation Guiding

Energy and water scarcity has become a major challenge in many regions of the world. Egypt is an arid/semiarid region with limited fresh water resources. So, a field study was conducted to investigate the growth responses of biofuel plant (Jatropha curcas L.) to a range of soil matric and osmotic potentials with foliar salicylic acid applications. Waters used were four different salinity levels, ranged from 0.32 to 7.0 dS m-1, and irrigation management was provided three different levels of soil matric potential: -6, -8 and -12 kPa. Irrigation process was guide lined using vacuum-gauge Tensiometer. Lab. pre-experiment indicated that relationship between Tensiometer readings and their corresponding soil moisture contents did not appear variation in the range of -6 to -15 kPa soil matric potential (where irrigation was managed). Therefore, Tensiometer apparatus could be used to guide irrigation process through a wide range of saline water on sandy soil. Obtained results indicated that, on early-growth stage, the most potential vegetative growth was performed when Jatropha irrigated with salinity level of 0.32 dS m-1 under matric potential ranged from -8 to -15 kPa, and there was no significant difference with that irrigated with 2.3 and 4.7 dS m-1. Therefore, and based on relationship among salinity, matric and osmotic potential, soil osmotic potential must be ganged from 2.5 to 7.5 bar to obtain potential vegetative growth. Regardless of salinity level, application of 5 mM SA can increase the vegetative growth characters under -8 to -15 kPa and appeared to give the most potential compared to 0 and 10 mM. Curves of J. crop coefficient, KC, were constructed over four years growing period. Such curves could provide facility for accurate irrigation schedule under similar studied region. Because of obtained results showed that both vegetative growth and seeds achieved the most performance under -8 to -15 k Pa , it is necessary to multiply KC values by 0.65. Additionally, weak sloping of curves indicates that Jatropha shrub already has low water requirements, particularly in the first three years. The most potential growth and capsule yield at mature stage was performed under treatment in which soil osmotic potential reached 2.9 bar (fresh water) compared to that of 7.2 bar (4.7 dS m-1). Application of 5 mM SA had a positive effect on both vegetative growth and capsule yield with 4.7dS m-1 salinity treatment, compared to those with fresh water. Also, values of leaf relative water content calculated at mature stage indicated that, there was no water deficit in leaf tissues between fresh irrigated and salt-stressed plants.