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

Abstract

Crop yield is primarily water-limited in areas of West Asia and North Africa with a Mediterranean climate. Ten years of supplemental irrigation (SI) experiments in northern Syria were conducted to evaluate water–yield relations for bread wheat ( Triticum aestivum L.) and durum wheat ( Triticum turgidum 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 during the growing season; the stress started from early March (stem-elongation stage) or even in seedling stage in a dry year, and from mid-April (anthesis) 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 ≥3 t ha −1 was ca. 60% higher than that with yield <3 t ha −1; this emphasises the importance of that to achieve effective use of water, optimal water supply and relatively high yields need to be ensured. Quadratic crop production functions with the total applied water were developed and used to estimate the levels of irrigation water for maximizing yield, net profit and levels to which the crops could be under-irrigated without reducing income below that which would be earned for full SI under limited water resources. The analysis suggested that irrigation scenarios for maximizing crop yield and/or the net profit under limited land resource conditions should not be recommended. The SI scenarios for maximizing the profit under limited water resource conditions or for a targeted yield of 4–5 t ha −1 were recommended for sustainable utilization of water resources and higher WUE. The time of irrigation was also suggested on the basis of crop sensitivity index to water stress taking rainfall probability and available soil water into account.