Dual probe heat pulse technique for measuring soil water content and sunflower water uptake

Soil water content is the most sought-after soil physical parameter. Recent experiments have shown that dual probe heat pulse (DPHP) sensors can be us ed to determine volumetric water content of soil without roots. Little wort ; has been done to document the performance of DPHP sensors in the presence of roots, and no work has been done with a taprooted plant. Thus, the obje ctive of this experiment was to determine the accuracy of DPHP sensors in m easuring volumetric water content (theta(v)) and changes in volumetric soil water content (Delta theta(v)) in soil with a branched taproot system. Ano ther objective was to determine plant water use. A sunflower plant (Heliant hus annuus L. 'Hysun 354') was grown in a column (0.20 m in diameter and he ight) with Haynie very fine sandy loam (coarse-silty, mixed, calcareous, me sic Mollic Udifluvents; FAO-Eutric Fluvisols) containing 11 DPHP sensors. R esults from the sensors were compared with those from the gravimetric metho d. Discrepancies between measurements of soil volumetric water content and changes of soil volumetric water by the DPHP and gravimetric methods were s mall (within 0.018 and 0.01 m(3) m(-3), respectively). The sunflower had a small amount of nocturnal transpiration, and roots took up water at a highe r rate near the surface of the soil than at deeper depths. The results show ed that the DPHP technique can monitor volumetric soil water content in the presence of a taproot. (C) 1999 Elsevier Science B.V. All rights reserved.