The West Asia‐North Africa (WANA) region, with a Mediterranean‐type climate, has an increasing deficit in cereal production, especially bread wheat (Triticum aestivum L.). Rainfed cropping coincides with the relatively cool, rainy winter season, usually from October to May. Cereal yields are low and variable in response to inadequate and erratic seasonal rainfall and associated management factors, such as lack of N and late sowing. In an area where water is limited, small amounts of supplemental irrigation (SI) water can make up for the deficits in seasonal rain and potentially produce satisfactory yields. This field study (1992–1993 to 1995–1996) on a deep clay soil (a Calcixerollic Xerochrept) in northern Syria was conducted for four growing seasons to assess the effects of SI (rainfed, 1/3, 2/3, and full irrigation) combined with N rate (0, 50, 100, and 150 kg ha−1) and sowing date (early, normal, and late) on one traditional (Mexipak 65) and three improved bread wheat cultivars (Cham 4, Cham 6, Gomam). Yields of rainfed wheat varied with seasonal rainfall and its distribution, with all main factors having significant effects. A delay in the sowing date from November to January consistently reduced yields and the response to both SI and N. With irrigation, crop responses were generally significant up to 100 kg N ha−1, while optimum response for rainfed conditions was with 50 kg N ha−1. An addition of only limited irrigation (1/3 full irrigation) significantly increased yields, but near maximum yields were obtained by 2/3 of full irrigation. Responses to N and SI were greatest for the higher‐yielding cultivars. Use efficiency for both water and N was greatly increased by SI. Thus, with minimum irrigation during the winter growing season combined with appropriate management, inputs, and varieties, wheat output could be substantially and consistently increased in the semiarid Mediterranean zone. Production functions developed from this dataset can help predict the effects of changing any of these parameters in other locations in the region.

Supplemental irrigation (SI) is defined as the application of a limited amount of water to rainfed crops when In West Asia and North Africa, shortage of water limits wheat precipitation fails to provide the essential moisture for (Triticum aestivum L.) production. Current irrigation practices aim at maximizing grain yield, but achieve lower return for the water normal plant growth. This practice has shown potential consumed. Maximizing water use efficiency (WUE) may be more in alleviating the adverse effects of unfavorable rain suitable in areas where water, not land, is the most limiting factor. patterns and thus improving and stabilizing crop yieldsWe examined the effects of various levels of supplemental irrigation (Perrier and Salkini, 1991;Oweis et al., 1998; Zhang (SI) (rainfed, 1/3 SI, 2/3 SI, full SI), N (0, 5, 10, 15 g N m Ϫ2 ), and and Oweis, 1999). Early studies at ICARDA showed sowing time (Nov., Dec., Jan.) on evapotranspiration (ET) and WUE that applying two or three irrigations (80-200 mm) to of wheat. WUE was calculated for rain (WUE r ), for total water (gross:wheat increased crop grain yield by 36 to 450%, and rain ϩ irrigation) (WUE g ), and for SI water only (WUE SI ). ET ranged produced similar or even higher grain yields than in fully from 246 to 328 mm for rainfed crops, with grain yield ranging from irrigated conditions (Perrier and Salkini, 1991; Oweis, 130 to 270 g m Ϫ2 and total dry matter from 380 to 1370 g m Ϫ2 . Irrigated 1994). Supplemental irrigation is widely practiced in crops had ET of 304 to 485 mm, with grain yield of 170 to 500 g m Ϫ2 . The degree to which water supply limits grain yield was indicated by Syria, and in southern and eastern Mediterranean counthe ratio of pre-to post-anthesis ET (2.1-2.4:1). The SI treatments tries. However, excessive use of water in SI because of significantly increased WUE g : from 0.77 to 0.83 to 0.92 kg m Ϫ3 in low irrigation cost and attractive gains from increased November and December sowings for 1/3 SI and from 0.77 to 0.92 yields has resulted in a decline of aquifers and deteriorakg m Ϫ3 in November sowing for 2/3 SI. The highest WUE g and WUE SItion of water quality in many areas (Ward and Smith, were achieved at 1/3 to 2/3 SI. WUE was substantially improved by 1994).applying 5 and 10 g N m Ϫ2 , with little increase for higher rates. DelayingIncreasing the portion of water used for plant transpisowing had a negative effect on WUE for both irrigation and rainfed ration through a large and early canopy can increase conditions. In this rainfed Mediterranean environment, WUE can be WUE. In Mediterranean environments, where crop cansubstantially improved by adopting deficit SI to satisfy up to 2/3 of opy development in winter is slow and rain occurs as irrigation requirements, along with early sowing and appropriate levels of N.

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8. Lessons Learned 309 9. Future Strategies 311 Acknowledgments 312 References 312With increasing global populations particularly in developing countries, and a limited or even shrinking supply of arable land, the challenge to agriculture is to meet the world's food and fiber needs without reducing the capacity of the resource base (soil and water) to enable guaranteed production for posterity and also to accommodate society's environmental and energy concerns. The issue of production sustainability is all the more acute in semi-arid and arid regions of the world where drought and related biophysical factors create a fragile and uncertain environment for production. In the West, mainly in temperate regions, long-term agronomic trials have been invaluable in identifying new technologies and crop management systems that have contributed to enhanced crop output that is sustainable from the biological, environmental, and economical standpoints. Many of these trials continue to guide cropping trends into the foreseeable future. The Mediterranean region has served climatic constraints to its agriculture and despite being cultivated for millennia, it is largely food deficient. Yet long-term cropping experiments that could direct agricultural production in a sustainable manner are relatively rare, and even most of such trials are of recent vintage. This review offers a background perspective on factors related to crop, production, and subsequently examines the various multiyear cropping system/ tillage trials in countries of North Africa and West Asia that border the Mediterranean. Special emphasis is given to the wide range of trials conducted in Syria by the International Center for Agriculture Research in the Dry Areas across a range of rainfall zones that are typical of the region as a whole. The goal of many trials was to identify cropping systems as a substitute for fallow and continuous cereal cropping with implications for improved water-use efficiency (WUE), crop quality, soil quality, and fertilizer use. Lessons learned from the trials are highlighted as well as future directions for cropping systems research.

Water supply is a major constraint to crop production for both chickpea and lentil in West Asia and North Africa, both of which have a Mediterranean climate. This study examined water use and water-use efficiency of chickpea and lentil from 3 experiments over 12 seasons, 1986–87 to 1997–98, in northern Syria. The strongest determinant of grain yield of chickpea and lentil and their water use under rainfed conditions is rainfall and its distribution. Large inter-seasonal fluctuations in weather resulted in larger inter-seasonal fluctuations in water use, and therefore in production of legumes. Seasonal evapotranspiration (ET) was significantly correlated with seasonal rainfall for both chickpea and lentil. Mean ET over 12 seasons was 268 mm for chickpea and 259 mm for lentil. The depth of extraction was, on average, 120 cm for chickpea and 80 cm for lentil. The average extractable soil water was 125 mm for chickpea and 90 mm for lentil over 12 seasons. For lentil, water-use efficiency for dry matter (WUEdm) and for seed yield (WUEgr) was 13.7 and 3.8 kg/ha.mm, respectively; for chickpea, WUEdm and WUEgr, 8.7 and 3.2 kg/ha.mm, respectively. Supplemental irrigation can significantly increase grain yield of both chickpea and lentil. However, there was less increase in grain yield in the wet seasons than in the dry seasons. Estimated soil evaporation was 80 mm for lentil and 105 mm for chickpea. The average transpiration efficiency was 7.1 kg/ha.mm for lentil and 6.4 kg/ha.mm for chickpea. Estimated potential transpiration efficiency for seed yield was 11.8 kg/ha.mm for lentil and 12.2 kg/ha.mm for chickpea. Both the average water-use efficiency and potential transpiration efficiency for lentil and chickpea were lower than those for cereals. Despite this, the rotation benefits and higher economic return provide the potential for these legumes to replace fallow or to break continuous cereal cropping in the region's farming system.