Salinity effects on grain yield and quality of malt barley in irrigated soils with water tables
Mathinya, Virginia Neo
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Global water scarcity and salinity of irrigated lands remains a concern. Shallow groundwater tables, often present in irrigation areas, may serve as energy efficient water sources, but they also restrict leaching of salts, especially in arid and semi-arid regions where high evapotranspiration exacerbates salinity. This study aimed at assessing salinity effects on water use, grain yield and grain quality of irrigated malt barley in the presence of a shallow groundwater table. The experiment was conducted over two seasons in lysimeters filled with a sandy Clovelly soil and a sandy loam Bainsvlei soil in which shallow saline groundwater table was maintained at a constant depth of 1.2 m. Cocktail barley cultivar was irrigated with five different irrigation water quality levels (ECi), i.e. control, 450, 600, 900 and 1200 mS m-1 made up of six different salts in varying amounts. Salinity of the groundwater table corresponded to irrigation water quality. Soil water balance was calculated from soil water measurements and used to determine crop water use. Seasonal salt balance of the root zone was also monitored. Saline irrigation water had cumulative effects on evapotranspiration, groundwater table depletion and grain yield as well as water productivity. Increasing irrigation water salinity from the control to the1200 mS m-1 ECi reduced grain yield by 91 and 89% for the Clovelly and Bainsvlei soil types, respectively, in the second season. Relationship between grain yield and salinity was better explained by the Van Genuchten & Gupta (1993) (R2=0.8) sigmoidal curve depicting the effect of ECe on grain yield of barley to be non-linear. Salinity (> 600 mS m-1) decreased 1000 seed weight and had no significant effect on germination characteristics. However, grain nitrogen, protein and sugar contents were increased by salinity. Nitrogen significantly increased above the cultivar’s inherent mean of 1.87%. Maltose was the only sugar not affected by both salinity and soil types. Increase in salinity reduced malt extract potential as indicated by lower (<7) germination index values for all treatments, seasons and soils with lower (<5.5) germination index values associated with the 900 and 1200 ECi mS m-1 treatments. This outcome may hold direct impact on barley producers as a lower premium is offered for lower quality grains. Therefore, further research is needed to explore interactive effects of salinity and other abiotic stresses on grain quality and the influence of cultivar variations. Furthermore, subsequent financial impact on grain processors need to be assessed.