Simulating Crop Phenological Responses to Water Deficits

Accurate phenology algorithms are fundamental for accurate simulation of crop growth. Phenology frequently changes as water becomes limiting, but such responses are poorly understood and difficult to quantify. Thus, these phenological responses are often ignored when modeling phenology. This chapter reviews the effects of water deficits on crop phenology and examines approaches used to simulate phenological responses to changes in water deficits. The dominant factors determining development rate are described, with particular attention given to the concept of thermal time and the correlation between thermal time and crop development rate for different phases of plant development. A survey of the literature to identify diverse phenological responses to water stress across species and genotypes is presented. Possible reasons for differences are discussed, and four mechanisms explaining phenological responses to water deficits are postulated. Different approaches for simulating phenological responses to changes in water deficits are described. Suggestions for improving the modeling of phenological development under water deficits are provided.