Plant Response to Water Stress and the Limitations of the Concept of Field Capacity.

Commonly, soil water balance models and irrigation management have relied on arbitrary limits defining the amount of plant available water (PAW) in the soil profile. These limits are widely known as permanent wilting point (lower limit, PWP) and field capacity (upper limit, FC). Even though the PWP typically represents a reasonable lower limit for plant transpiration and seems to be well characterized by a matric potential of -1500 kPa, the concept of FC has no clear physical meaning, has several definitions in terms of matric potential, and its determination across field, pot experiments, and lab routines may not be consistent. In this study we conducted a series of experiments using corn plants in a controlled environment growth chamber to analyze alternative upper limits to FC such as saturation point and 10% air filled porosity. We also examined the use of soil hydraulic conductivity as a potential predictor of plant transpiration under atmospheric demands of 5 and 8.5 mm of reference evapotranspiration (ETo).