Root Length Density of Rainfed Fig Trees under Different Times, Amounts, and Positions of Supplemental Irrigation

The changes in Root Length Density (RLD) of rainfed fig trees due to supplemental irrigation were studied during two growing seasons in Estahban, southern Iran, with objective of finding out the optimum position, time, and amount of supplemental irrigation. Irrigation position treatments were: (1) In a micro-catchment close to tree trunks; (2) Inside the tree canopies (1-1.1 m from tree trunks); and (3) Outside the tree canopies (2.1-2.2 m from tree trunks). Irrigation time treatments included: (a) In early spring and (b) In mid-summer; and the treatments of irrigation amount were: (i) No supplemental irrigation (control), (ii) 1,000, and (iii) 2,000 L per tree. Results showed that the highest RLD in different irrigation amounts occurred at 15-45 cm depth during late winter and late spring. However, during summers, the high RLD occurred 15 cm lower at 30-60 cm depth. Irrigation water treatments of 1,000 and 2,000 L per tree increased RLD values by 11.3 and 19.3%, respectively, in late spring and 10.5% and 14.7%, respectively, in late summer, compared with the rainfed treatment. Whereas this increase generally occurred in the wetted area; supplemental irrigation out of tree canopy could develop the root horizontal extension to a greater distance. Lower temporal variation in RLD profile was obtained for depths deeper than 75 cm, which was in agreement with soil water content variations. Supplemental irrigation applied out of tree canopy with 2,000 L per tree (200 m(3) ha(-1)) during early spring is recommended to improve root development of fig trees in drought prone rainfed areas.