FOLIAR AND ROOT ABSORPTION OF NA- IN MAIZE AND BARLEY - IMPLICATIONS FOR SALT TOLERANCE SCREENING AND THE USE OF SALINE SPRINKLER IRRIGATION( AND CL)

Above-canopy sprinkler irrigation with saline water favours the absorp tion of salts by wetted leaves and this can cause a yield reduction ad ditional to that which occurs in salt-affected soils. Outdoor pot expe riments with both sprinkler and drip irrigation systems were conducted to determine foliar ion accumulation and performance of maize and bar ley plants exposed to four treatments: nonsaline control (C), salt app lied only to the soil (S), salt applied only to the foliage (F) and sa lt applied to both the soil and to the foliage (F + S). The EC of the saline solution employed for maize in 1993 was 4.2 dS m(-1) (30 mM NaC l and 2.8 mM CaCl2) and for barley in 1994, 9.6 dS m(-1) (47 mM NaCl a nd 23.5 mM CaCl2). The soil surface of all pots was covered so that in the F treatment the soil was not salinized by the saline sprinkling a nd drip irrigation supplied nutrients in either fresh (treatments C an d F) or saline water (treatments S and F + S). Saline sprinkling incre ased leaf sap Na+ concentrations much more than did soil salinity, esp ecially in maize, even though the saline sprinkling was given only two or three times per week for 30 min, whereas the roots of plants grown in saline soil were continuously exposed to salinity. By contrast, le af sap Cl- concentrations were increased similarly by saline sprinklin g and soil salinity in maize, and more by saline sprinkling than salin e soil in barley. It is concluded that barley leaves, and to a greater extent maize leaves, lack the ability to selectively exclude Na+ when sprinkler irrigated with saline water. Moreover, maize leaves selecti vely absorbed Na+ over Cl- whereas barley leaves showed no selectivity . When foliar and root absorption processes were operating together (F +S treatment) maize and barley leaves accumulated 11-14% less Na+ and Cl- than the sum of individual absorption processes (treatment F plus treatment S) indicating a slight interaction between the absorption pr ocesses. Vegetative biomass at maturity and cumulative plant water use were significantly reduced by saline sprinkling. In maize, reductions in biomass and plant water use relative to the control were of simila r magnitude for plants exposed only to saline sprinkling, or only to s oil salinity; whereas in barley, saline sprinkling was more detrimenta l than was soil salinity. We suggest that crops that are salt tolerant because they possess root systems which efficiently restrict Na+ and Cl- transport to the shoot, may not exhibit the same tolerance in spri nkler systems which wet the foliage with saline water.