Microtensiometer technique for in situ measurement of soil matric potential and root water extraction from a sandy soil

Abstract

The suitability of microtensiometers to measure the spatial variation of soil matric potential and its diurnal change was tested in a pot experiment with pearl millet (Pennisetum americanum [L.] Leeke) in a sandy soil as the soil dried out.The temporal and spatial resolution of this technique allowed precise measurement of soil matric potential and thus estimation of soil water extraction from different compartments as well as from the whole rooting zone. The technique also allowed the measurement of rehydration of plants at night and root water uptake rate per unit soil volume or per unit root length. The precision of determination of root water uptake depended greatly on the accuracy of the estimate of hydraulic conductivity, which was derived from a bare soil and might be different for a cropped soil owing to aggregation induced by the root system. A linear relationship between root length and water uptake was found (r 2= 0.82), irrespective of variation in soil water content between compartments and despite the variation in root age, xylem differentiation and suberin formation expected to exist between different compartments of the rooting zone. As the experiment was carried out in a range of soil matric potentials between -4 and -30 kPa, drought stress did not occur. Further information at lower soil matric potentials are required, to address questions such as the importance of soil resistance for water uptake, or which portion of the root system has to be stressed to induce hormonal signals to the shoot. The microtensiometer technique can be applied to soil matric potentials up to -80 kPa.

Use of a microtensiometer technique to study hydraulic lift in a sandy soil planted with pearl millet (Pennisetum americanum [L.] Leeke)

“…Plants rehydrate at night and therefore water uptake from the soil continues (Fig. 2) even though under these conditions transpiration is not detectable (Vetterlein et al, 1993). Whether plants are able to equilibrate with the soil at night depends on soil resistance to water flux, which in turn decreases as soil dries out.…”

“…The application of radioactive tracers, however, does not allow the distinction between root grafting, transfer via connecting fungal mycelium and water release into the soil. The aim of the following pot experiment with pearl millet in a sandy soil was to measure hydraulic lift using the microtensiometer technique (Vetterlein et al, 1993), which provides a precise direct measurement of soil matric potential at specific locations through time.…”

Do roots mind the gap?

“…Plants were grown under controlled conditions (23°Cday/23°C night; 65 % relative humidity; 14 h photoperiod with 350 μmolm −2 s −1 ) in a climate chamber. Microtensiometers as described by Vetterlein et al (1993) were inserted at depths of 5 cm and 18 cm. Throughout the experiment each column was placed on a balance and the weight was continuously recorded (10 min interval).…”

Effects of plant roots on soil-water retention and induced suction in vegetated soil

“…Note that S. heptaphylla is not a crop species, and thus it does not need to be grown in soil that has rich organic contents and nutrient concentration (Vetterlein et al, 1993;Roberts, 2000). S. heptaphylla also does not require frequent irrigation and harvesting (Carrow et al, 1996;Hau and Corlett, 2003), which are usually important for crop species when crop yield is of concern (Zhang et al, 2004).…”