Irrigation with brackish water under desert conditions IV. Salt tolerance studies with lettuce (Lactuca sativa L.)

In a field trial, three Romaine lettuce cultivars and seven iceberg lettuce cultivars were drip irrigated from day 20 after planting with water of four levels of salinity (electrical conductivity of 1.2, 3.5, 8.2 and 10.5 dS/m). The Romaine lettuce cultivars were far more tolerant to salinity than the iceberg cultivars. There were no specific salt-tolerant cultivars within either of the two cultivar groups. The slope of the linear regression of relative yield vs. salinity was -5.6 for the iceberg lettuce cultivars, which is half the value reported elsewhere for lettuce. Iceberg lettuce appears to be more sensitive to salinity at later than at early growth stages. There was no apparent osmotic adaptation of lettuce to salinity. The osmotic potential of the leaves decreased to -1.3 MPa about a month after planting and then gradually increased to -0.6 MPa.