EFFECTS OF ROOT DENSITY DISTRIBUTION MODELS ON ROOT WATER UPTAKE AND WATER FLOW UNDER IRRIGATION.

Water uptake by roots greatly influences water distributions in soil-plant systems. It is essential to understand root water uptake patterns to estimate accurately water movement through the systems. In this study, six empirical root density distribution models were incorporated into a water flow model to study their effect on root water uptake and soil water movement. Two main distributions of root systems, i.e., cylindrical and conical shapes, were considered. Root water uptake with these models was evaluated at three levels of irrigation, about 0.3, 0.7 and 1.0 of total potential transpiration, with three root depths in a sandy loam soil and a silt loam soil. High irrigation levels reduced difference of root water uptake from different root depths in both soils. In the sandy loam soil, a shallow root depth could enhance difference in root water uptake among different root distribution models, whereas a greater difference was found within larger root depths in the silt loam soil. The models with the conical shape resulted in an average of 13% higher leaching in the sandy loam soil than were seen with the cylindrical shape. Contributions from different parts of the root system to the total root water uptake were varied with the different models, as were the distributions of water pressure head and water flux in the soil profiles.