Cropping systems and crop complementarity in dryland agriculture to increase soil water use efficiency: a review

Dryland agriculture under rainfed conditions is found mainly in Africa, the Middle East, Asia, and Latin America. In the harsh environments of Sub-Saharan Africa (SSA) and West Asia and North Africa (WANA), water is the principal factor limiting crop yield. A review has been carried out on soil and crop management research that can increase the water use efficiency. The WANA production systems are dominated by cereals, primarily wheat in the wetter and barley in the drier areas, in rotation with mainly food legumes such as chickpea, lentil and forage legumes. The SSA production systems are generally characterized by cereal/ legume mixed-cropping dominated by maize, millet, sorghum, and wheat. The major constraints in both regions to crop production are low soil fertility, insecure rainfall, low-productive genotypes, low adoption of improved soil and crop management practices, and lack of appropriate institutional support. Different cropping systems and accompanying technologies are discussed as well as selected examples of impact of these technologies. Results indicate that there is an advantage to apply these technologies but being function of socio-economic and bio-physical conditions. It is recommended that future research focuses on integrated technology development while taking into account also different levels of scale such as field, village, and watershed.