IMPROVING PRODUCTIVITY OF CROPS IN WATER-LIMITED ENVIRONMENTS

This review deals with improving the performance of dryland crops in dry, mainly semiarid, environments. Although such crops are often limited by water, the development of the notion of water-limited potential yield has shown that their yields are often limited strongly by other factors. These factors are explored by dissecting the water-limited potential yield into a framework involving four largely independent components, namely, the potential water supply for the crop; the fraction of that water supply that is transpired; the efficiency with which the crop exchanges water for CO, in producing biomass (Transpiration Efficiency); and the fraction of the biomass that ends up in the grain (Harvest Index). This framework is used to explore a wide range of agronomic possibilities for managing crops so as to get close to the water-limited potential, including managing previous crops, forages and fallows to increase soil water at sowing; reducing evaporative losses from the soil surface; ensuring that sowing and flowering occur at the right times; maximizing soil water extraction by the crop; and ensuring that there is adequate water available during late floral development and grain filling. Such operations often involve trade-offs and risks that must be managed.