Assessing and Modifying Macroscopic Root Water Extraction Basil (Ocimum basilicum) Models under Simultaneous Water and Salinity Stresses

In arid and semiarid regions, plants are often subjected to both water scarcity and soil salinity. Our objectives were to compare several equations describing the combined effects of water and salinity stress on root water uptake and to improve one of the equations. Consequently, seven macroscopic root water extraction models were evaluated using basil (Ocimum basilicum L.) experimental data. An experiment was conducted with four irrigation water salinities [1.175 (S-1), 3 (S-2), 5 (S-3), and 8 (S-4) dS m(- 1)] and four irrigation levels: 120 (W-1), 100 (W-2), 80 (W-3), and 60% (W-4) of crop water requirements, each with three replicates. Among the root water uptake models, the modified Homaee et al. model provided the best agreement with the experimental data. Because of the high sensitivity of basil to both water and salinity stresses, the root water uptake threshold value was low. Increased salinity decreased the potential at which the root water uptake ceased. These values for S1, S2, S3, and S4 were 3184, 2750, 2215, and 1650 cm, respectively. The h(3) parameter (the threshold soil water pressure head in linear root water extraction models) was also influenced nonlinearly by salinity: h3 under the S1, S2, S3, and S4 salinity treatments were 510, 481, 354, and 295 cm, respectively. These findings can be used for scheduling irrigation accurately, determining actual crop water requirements and thus managing the quantity and quality of irrigation water more efficiently, and solving the Richards-Darcy equation more precisely by determining the root water uptake value.