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-Sah aran Africa (SSA) and West Asia and North Africa (WANA), water is the princ ipal 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 th e wetter and barley in the drier areas, in rotation with mainly food legume s such as chickpea, lentil and forage legumes. The SSA production systems a re generally characterized by cereal/ legume mixed-cropping dominated by ma ize, millet, sorghum, and wheat. The major constraints in both regions to c rop production are low soil fertility, insecure rainfall, low-productive ge notypes, low adoption of improved soil and crop management practices, and l ack of appropriate institutional support. Different cropping systems and accompanying technologies are discussed as w ell as selected examples of impact of these technologies. Results indicate that there is an advantage to apply these technologies but being function o f socio-economic and bio-physical conditions. It is recommended that future research focuses on integrated technology development while taking into ac count also different levels of scale such as field, village, and watershed.