Effects of Water Stress on Crop Production

Water stress is due to a low water potential in the plant caused by low soil water potential, high evaporative demand, and/or a high resistance to water flow through the plant. The water deficit affects many crop processes, although most are related to the reduction in expansive growth, the most sensitive process, and stomatal closure. Mild to moderate deficits do not generally affect the harvest index, and in some species, they may increase it. However, severe water deficits reduce the harvestHarvest index (HI). The effect of water stress on crop yield can be quantified by Stewart's equation, which establishes that the relative yield reduction is directly proportional to the relative reduction in evapotranspiration (ET), with an empirical coefficient (Ky) which ranges between 0.8 and 1.5. More mechanistic models may be used to characterize the yield responses to variable water supply, but they need local calibration for accuracy.