Modeling sorghum response to irrigation water salinity at early growth stage

• Salinity threshold value for sorghum is 1 dS/m at seedling stage.
• Seedling rate of sorghum reduces to 50 percent at 11 dS/m soil salinity.
• All linear and nonlinear salinity response models overestimate threshold value.

Agricultural water management in arid and semi-arid regions largely depends on availability and quality of irrigation water at different plant growth stages. In saline environments, plant response to salinity varies at different growth stages. Information on plant response to salinity at various growth stages can be used in managing saline waters for irrigation. This study was conducted to quantitatively assess response of sorghum (Sorghum bicolor L. Moench) to salinity at seedling stage. Consequently, an extensive experiment in natural saline sandy loam soil with five natural saline water treatments including 4, 6, 8, 10, and 12 dS/m was conducted. The reason for selecting natural sources of saline water and a saline soil was to minimize deviations from natural conditions under which sorghum grows. Sorghum seeds were planted and seedles counted at 24 h time intervals. The macroscopic models of Maas and Hoffman, van Genuchten and Hoffman, Dirksen et al., and Homaee et al. were used to predict relative seedlings at different salinity levels. The obtained results indicated that salinity threshold value EC* for sorghum at seedling stage is 1 dS/m and the seedling rate reduces to 50 percent at 11 dS/m of soil salinity. All evaluated models overestimated the EC* value. Calculated statistics indicated that the nonlinear salinity models are more accurate than the linear model. Among those, Homaee et al. model provided better predictions at seedling growth stage.