MODELING ROOT WATER POTENTIAL AND SOIL ROOT WATER TRANSPORT .2. FIELD COMPARISONS

In a previous article, a theoretical approach to the calculation of root water potential (RWP) and water uptake by roots in the two-dimensional case was proposed. The RWP was assumed to show a threshold value that controlled plant transpiration by means of chemical messages triggered by roots. This article compares model predictions with data from field experiments. Measured maximum evapotranspiration (MET), basic soil hydraulic properties, and a map of soil-root contacts in a soil profile (vertical case) were taken as inputs to the model. Field experiments were performed in a clay loam soil (a Typic Hapludalf) planted with maize (Zea mays L., F1 hybrid LG1), where sections were compacted using wide tractor wheels. At silking, precise maps of soil-root contacts were drawn for vertical planes. Volumetric water content and matric potential measurements were performed during a 17-d experiment under dry climatic conditions. Computed and field-measured soil volumetric water content values showed large gradients between compacted and noncompacted zones. Calculated and measured mean root water-uptake rates were similar, and depended strongly on root densities. Mean individual root water-uptake rates were considerably greater in zones where the root density was low. Finally, the proposed model could be useful for calculating the root water potential if chemical messages from roots are confirmed as being an important control mechanism of stomatal conductance and photosynthesis.