INFLUENCE OF GENOTYPE, WATER AND N ON LEAF WATER RELATIONS IN NO-TILL WINTER WHEAT

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Abstract
Field studies were established at four locations in 1985 and 1986 to study the physiological responses of two winter wheat (Triticum aestivum L.) cultivars under different water and nitrogen regimes. Measurements of leaf water potential (ψ1), osmotic potential (π) and leaf conductance (g1) were made on individual leaves at regular intervals throughout the growing season. Values of ψ1 ranged from −1.0 to −4.5 MPa, indicating that winter wheat in Saskatchewan experiences moderate to extreme levels of water stress. Leaf ψ1 levels generally decreased as evaporative demand for water increased. Osmotic potential values ranged from −1.0 to −4.0 MPa while ψp (calculated as ψp = ψ1 − π) ranged from −0.4 to 0.9 MPa. Despite strong osmotic adjustment in response to stress, positive ψp was not always maintained. Additional water through limited irrigation increased both ψ1 and π but did not significantly affect ψp. Fertilizer N additions consistently decreased both ψ1, and π, and in some cases ψp levels. The tall cultivar Norstar displayed greater turgor maintenance than the semidwarf cultivar Norwin under both stress and nonstress conditions. Leaf conductance ranged from approximately 0.04 – 1.10 cm s−1 and was higher in irrigated plots. Fertilizer N additions often decreased g1 per unit area of leaf. On a leaf area basis, g1 for Norwin at high N levels was often greater than for Norstar. However, similar g1 vs. ψ1 responses for Norwin and Norstar indicated a similar stomatal response to increased water stress for these cultivars.Key words: Drought stress, nitrogen, leaf conductance, turgor potential