With 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.

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Long‐Term Cereal‐Based Rotation Trials in the Mediterranean Region: Implications for Cropping Sustainability

Nitrogen and water effects on wheat yield in a Mediterranean-type climate: I. Growth, water-use and nitrogen accumulation

13 – Drought Tolerance and Water Use Efficiency

Global change is not restricted to climate change, and plant species generally face multiple human-driven disturbances constraining their viability Most importantly, interactions among these drivers frequently generate nonadditive effects that cannot be predicted based on single-factor studies Our goal was to assess the joint effects of three global change drivers that are especially relevant in Mediterranean ecosystems, namely, fragmentation, reduced habitat quality, and climate change on Centaurea hyssopifolia, a gypsum specialist plant We carried out a two-year study (2005-2006) in natural populations of this plant in large (>11 ha) and small (< 15 ha) fragments Within each fragment, we identified areas of contrasting habitat quality as revealed by plant cover and nutrient content, and within each combination of habitat quality and fragment size we performed a rainfall manipulation experiment simulating the most likely future climate scenario for the region Survival, growth, phenology, and reproductive success of selected plants were monitored The three drivers profoundly affected responses of Centaurea hyssopifolia in both study years, phenology being mainly affected by changes in habitat quality and reductions in rainfall and reproductive traits being mainly affected by fragmentation Plants in sites of poor habitat quality and plants in the dry treatment advanced most of their phenophases (flowering and dispersing earlier) and showed reduced growth rate and increased fraction of senescent leaves Plants growing in small fragments had lower survival, lower number of viable seeds, and a reduced seed set compared to those from large fragments We found significant synergistic interactions among drivers For example, the interaction between fragmentation and habitat quality led to lower survival and lower relative growth in plants from small and poor-quality habitat sites Our results highlight the importance of studies addressing simultaneously all relevant drivers of global change potentially affecting plant performance under natural conditions In addition, the complex responses of phenology and reproductive traits of C hyssopifolia emphasize the need for studies integrating traits from vegetative to reproductive and from the organ to the whole-plant level

Impact of three global change drivers on a Mediterranean shrub.

Barley (cv. Beecher) was grown at two sites (Jindiress and Breda) in northern Syria, chosen for their contrasting edaphic and climatic conditions. At both sites, three fertilizer treatments were applied zero (Z), 60 kg P2O5/ha (P), and 60 kg P2O5/ha with 60 kg N/ha (NP) and measurements made of shoot and root growth, and water use.The growth of crops not given fertilizer was similar at both sites and early growth was increased by the application of fertilizers. However, at maturity, yield was increased at Jindiress by giving N and P together, but not by P alone, while at Breda P alone increased yields but additional N produced no additional yield. There were marked effects of fertilizer on crop development at Jindiress; anthesis and maturity were about 14 days earlier in the NP treatment than in the Z treatment.Root growth was also affected by fertilizer applications and there were small but significant differences in growth between the sites. The proportion of root weight: total plant weight was greater than commonly observed in temperate cereals and there were substantial differences between the sites in the pattern of root distribution within the soil profile.The total amount of water used by the crops differed between the sites but was largely unaffected by fertilizer treatment at each site. Evapotranspiration during the winter when the soil was recharged with water was about 50% of the seasonal total. At Jindiress, the pattern of water extraction from the profile and the root distribution were similar before flowering but at Breda, there was no correspondence. Rates of water inflow varied with both site and time.Crop characteristics that may be associated with increased yields are discussed. Deeper, more extensive rooting is unlikely to be useful in such regions but rapid early growth of both shoots and roots may allow water to be used more efficiently.

Colin Webb

Papers

Soil Water and Nitrogen in Mediterranean-type Environments