Plant stress resulting from lack of an adequate water supply throughout the growing season represents the single greatest limitation to attainment of genetic yield potential of essentially all crop plants. Plant water stress occurs when the soil water supply is inadequate to meet the crop water demand defined by atmospheric conditions. The volume of water contained in the root zone defines soil water supply. Soil texture determines the water holding capacity (volume of H₂O/volume of soil) of the soil system. Rooting depth and density determine how much of the total soil volume can be extracted. The daily crop water consumption (transpiration) is determined by the evaporative demand the atmosphere and the crop size and structure (leaf area and light interception).