Irrigation with brackish water under desert conditions II. Physiological and yield response of maize (Zea mays) to continuous irrigation with brackish water and to alternating brackish-fresh-brackish water irrigation

The physiological behavior and yield response of maize under irrigation with saline water was studied in the laboratory and in the field. In the laboratory, the germination rate decreased only when the electrical conductivity (EC) of the substrate solution was above 17 dS/m. The osmotic potential of germinating maize seedlings decreased in proportion to the decrease in osmotic potential of the substrate. In the field, two maize cultivars (a field maize and a sweet maize) were irrigated alternately with saline (11 days from sowing), fresh (21 days from emergence), and saline (from day 33 to harvest) water and compared with maize irrigated with saline water continuously throughout the season. Four levels of irrigation water salinity were used (EC_i = 1.2, 4.5, 7.0 and 10.5 dS/m). In the field no osmotic adjustment by the leaf sheaths of plants in response to salinity was observed. The osmotic potential of corn leaf sheaths (π) decreased with ontogeny in all treatments. The midday leaf water potential (ψ_L) in maize irrigated with 10.5 dS/m water was 0.75 MPa lower than in plants irrigated with 1.2 dS/m water. In the continuous treatment grain yield was reduced significantly with each increase in salt concentration, and the relationship between relative yield (y) and EC_i could be expressed as y = 100-8.7 (EC_i-0.84). With alternating irrigation and 7.0 dS/m treatment the grain yield was the same as in the low EC treatment (6.98 kg/m²).