Parametric modeling of root length density and root water uptake in unsaturated soil

The problem of water movement through the root zone has attracted increasing interest during the last few decades. In this research, the spatial and temporal pattern of root water uptake in wetted soil was studied in the root zone of a 6-year-old apple tree. An important part of the root water uptake model is root length density, which was measured by sampling soil cores in one quarter of the root zone. The exponential model better described the observed apple root distribution. The measured data were compared against the outputs of the root density distribution model. A normalized root length density was used to simulate root water uptake and determine the effect of root distribution on the water content pattern. A 2-dimensional (2D) model of root water uptake was established, which includes root density distribution function, potential transpiration, and the soil water stress-modified factor. Root water uptake distribution was measured with an array of time domain reflectometry (TDR) probes. Root water uptake parameters were optimized by minimizing the residuals between measured and simulated soil water content values. Studies showed that the maximum root water uptake was at a depth of 10-50 cm. The results indicated an excellent agreement between the measured and the simulated values, proving that the developed root water uptake model is effective and feasible.