Management alternatives for improved durum wheat production under supplemental irrigation in Syria

In the Mediterranean zone, efforts to optimize combinations of supplemental irrigation (SI), improved varieties, nitrogen (N) and sowing dates aim to improve and stabilize cereal yields and maintain quality, especially for du rum wheat. Thus, a 4 year field study (1992/1993 to 1995/1996) on a deep cl ay soil in northern Syria assessed the impact of SI (rain-fed, 1/3, 2/3 and full SI) combined with variable N application rates (0, 50, 100, 150 kg ha (-1)) and sowing date (early, normal, late) for four improved durum wheat v arieties adapted to rain-fed and irrigated conditions. As rainfall and evap otranspiration varied over the 4 years, the amount of SI water required als o varied. Yields varied with the season, and the main factors, except varie ty, were significant. Delaying sowing from November to January reduced yiel ds and response to both SI and N. With irrigation, crop responses were gene rally significant up to 100 N ha(-1), whereas the optimum response for rain -fed conditions occurred with 50 kg N ha(-1). Limited SI (1/3) significantl y increased yields, but almost maximum yields were obtained by 2/3 of full SI. Water- and N-use efficiencies were greatly increased by SI, with little variation among varieties. However, irrigation and delayed sowing decrease d grain protein levels, which were partially compensated for by added N. A similar effect was observed for kernel vitreousness. Models developed from the response data can facilitate the potential transfer of these findings. Thus, in most growing seasons, minimum irrigation during the winter growing season, combined with appropriate fertilization, can enhance wheat output and yet maintain grain quality. (C) 1999 Elsevier Science B.V. All rights r eserved.