Of these factors, water stress is one of the major causes of yield variability in fields. Water stress occurs when roots cannot supply enough water to satisfy evaporative demand of water transpiring from leaves. Root water uptake is a function of soil water availability, root depth and density, and location of roots relative to water in the soil. Plant genetics also can influence root growth and development, and subsequently water uptake, by influencing location of roots relative to water in the soil. Daily evaporative demand driving transpiration and potential water stress is a function of uncontrollable environmental factors, including temperature, relative humidity, and wind speed.
Water stress reduces photosynthesis, resulting in reduced crop growth and yield.
Minor water stress often occurs for short periods during the hottest part of the day, late in the season. Water stress can vary across a field, depending upon soil type, moisture-holding capacity, and drainage characteristics. The integration of variable water stress each day over the season can result in reduced photosynthesis and variable yield loss across a field. Because of the dynamic nature of water stress, it is very difficult to measure and correlate to final yield. Iowa State University researchers are using crop models to study the role of water stress in creating yield variability.