Does transport of water to roots limit water uptake of field crops?

Abstract

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 investigate the general model behaviour. A sensitivity analysis showed that initial volumetric water content and root length density are of greater importance than root diameter in determining the maximum water transport rate to the roots. Data from a field experiment were taken, describing root length density, volumetric water content and water uptake rates under oats (Avena saliva L.) and faba beans (Vicia faba L.) as model input parameters. With this data the model calculated the water content difference between the bulk soil and the root surface which is necessary to induce a water flow to the roots matching the observed water uptake rate. Root length densities below the grain legume crop faba beans are one order of magnitude lower compared to that of the cereal crop oats. The therefore higher specific water influx rates of faba beans roots resulted in a higher decrease in water content near the root surface. However, water uptake by faba beans was controlled by the water flow towards the roots probably only in deeper soil layers with very low root length density. For the given conditions no transport limitation of water uptake was calculated, when rooting densities were higher than about 0.1 cm.cm−3.

STICS: a generic model for the simulation of crops and their water and nitrogen balances. I. Theory and parameterization applied to wheat and corn

“…It equates to an average soil-root distance of 0.8 cm, within the interval proposed by Aura [8] (between 0.5 and 1 cm). However, Kage and Ehlers [89] and Robertson et al [136] proposed lower optimal densities (0.1 and 0.25 cm cm-3 soil, respectively).…”

Root traits of cup plant, maize and lucerne grass grown under different soil and soil moisture conditions

“…Except for Dasselsbruch, the RLD of cup plant fell below 0.5 or even 0.1 cm cm À3 in soil layers beneath 100 cm depth (Figures 1 and 4). The minimum RLD that still allows for a rapid soil water extraction down to the permanent wilting point has been considered to be 0.1 cm cm À3 by Kage and Ehlers (1996) and 0.5-1.0 cm cm À3 by De Willingen et al (2000). In the partially highly compacted soil of the experimental field at Braunschweig, lucerne grass met the condition of a RLD > 0.1 cm cm À3 in the entire rooted profile (Figure 4).…”

Effects of varied water regimes on root length, dry matter partitioning and endogenous plant growth regulators in sunflower (Helianthus annuusL.)

“…The development of crop leaf area is controlled by the amount of assimilates allocated to the leaves and determines radiation interception and therefore transpiration and assimilate production (Jones 1992, Campbell & Norman 1998. Water uptake may be limited by the amount of roots in a particular soil layer (Klepper et al 1983, Klepper 1990, Kage & Ehlers 1996 and enhanced root growth can reduce drought stress. An optimal partitioning of dry matter between root and shoot, and the further separation of aboveground DM between the vegetative and reproductive organs therefore is of crucial importance for crop yield under drought stress.…”