The impact of saline water irrigation management options in a dune sand on available soil water and its salinity

In this study the effect of two levels of irrigation input, each at two frequencies, were assessed on sorghum (Sorghum bicolor (L.) Moench) grain yield as impacted by available soil water after irrigation and the electrical conductivity of soil water (ECsw) in a dune sand, in a greenhouse experiment. Saline water (7.32 dS m−1) at input amounts equivalent to 50% or 100% of pan evaporation was applied daily or every second day. Using time domain reflectometry technique, soil water content and ECsw were monitored simultaneously just before and 1–2 h after irrigation. The cumulative recharge by irrigation in the top 25 cm of the profile ranged from 309 to 662 mm and it depended on irrigation input amounts, which ranged from 382 to 765 mm, and frequency. The potential cumulative evapotranspiration (ETc) was 578 mm. The daily recharge matched against the corresponding ETc indicated that grain yield might have been impacted by water stress in the 50% irrigation input, regardless of the frequency, but not in the 100% input treatment. The daily ECsw in the root-zone matched against the FAO threshold (13.6 dS m−1) indicated the possibility of salinity stress during the late maturity stage in the 50% input treatment, regardless of the irrigation frequency, but no stress in the 100% input treatment. Though there was no water or salinity stress in the every second day irrigated 100% input treatment, the significant relative yield reduction, compared with the daily 100% input, is attributed to inherent limited available soil water capacity and rapid percolation losses between irrigations in this sand. The results indicate daily irrigation at 100% input is the most appropriate saline water irrigation management option for this dune sand.