Water-yield relations and optimal irrigation scheduling of wheat in the Mediterranean region

Crop yield is primarily water-limited in areas of West Asia and North Afric a with a Mediterranean climate. Ten years of supplemental irrigation (SI) e xperiments in northern Syria were conducted to evaluate water-yield relatio ns for bread wheat (Triticum aestivum L.) and durum wheat (Triticum turgidu m L.), and optimal irrigation scheduling was proposed for various rainfall conditions. The sensitive growth stages of wheat to water stress were from stem elongation to booting, followed by anthesis, and grain-filling. Water stress to which crop subjected depends on rainfall and its distribution dur ing the growing season; the stress started from early March (stem-elongatio n stage) or even in seedling stage in a dry year, and from mid-April (anthe sis) in an average or wet year. Crop yield linearly increased with increase in evapotranspiration (ET), with an increase of 160 kg for bread wheat and of 116 kg for durum wheat per 10 mm increase of ET above the threshold of 200 mm. Water-use efficiency (WUE) with a yield greater than or equal to 3 t ha(-1) was ca. 60% higher than that with yield <3 t ha(-1); this emphasis es the importance of that to achieve effective use of water, optimal water supply and relatively high yields need to be ensured. Quadratic crop produc tion functions with the total applied water were developed and used to esti mate the levels of irrigation water for maximizing yield, net profit and le vels to which the crops could be under-irrigated without reducing income be low that which would be earned for full SI under limited water resources. T he analysis suggested that irrigation scenarios for maximizing crop yield a nd/or the net profit under limited land resource conditions should not be r ecommended. The SI scenarios for maximizing the profit under limited water resource conditions or for a targeted yield of 4-5 t ha(-1) were recommende d for sustainable utilization of water resources and higher WUE. The time o f irrigation was also suggested on the basis of crop sensitivity index to w ater stress taking rainfall probability and available soil water into accou nt. (C) 1999 Elsevier Science B.V. All rights reserved.