H. Kage et W. Ehlers, DOES TRANSPORT OF WATER TO ROOTS LIMIT WATER-UPTAKE OF FIELD CROPS, Zeitschrift fur Pflanzenernahrung und Bodenkunde, 159(6), 1996, pp. 583-590
The question was examined under which conditions the water extraction
rate of plant roots in the field can be limited by water transport to
the roots. For this purpose we used a numerical solution of the single
root model. Scenario calculations were carried out in order to invest
igate the general model behaviour. A sensitivity analysis showed that
initial volumetric water content and root length density are of greate
r importance than root diameter in determining the maximum; water tran
sport rate to the roots. Data from a field experiment were taken, desc
ribing root length density, volumetric water content and water uptake
rates under oats (Avena sativa L.) and faba beans (Viciafaba L.) as mo
del input parameters. With this data the model calculated the water co
ntent difference between the bulk soil and the root surface which is n
ecessary to induce a water flow to the roots matching the observed wat
er uptake rate. Root length densities below the grain legume crop faba
beans are one order of magnitude lower compared to that of the the ce
real crop oats. The therefore higher specific water influx rates of fa
ba beans roots resulted in a higher decrease in water content near the
root surface. ver, water uptake by faba beans was controlled by the w
ater flow towards the roots probably only in deeper soil layers with v
ery low root length density. For the given conditions no transport lim
itation of water uptake was calculated, when rooting densities were hi
gher than about 0.1 cm . cm(-3).