A split-pot experiment with sorghum to test a root water uptake partitioning model

Abstract

Correct modeling of root water uptake partitioning over depth is an important issue in hydrological and crop growth models. Recently a physically based model to describe root water uptake was developed at single root scale and upscaled to the root system scale considering a homogeneous distribution of roots per soil layer. Root water uptake partitioning is calculated over soil layers or compartments as a function of respective soil hydraulic conditions, specifically the soil matric flux potential, root characteristics and a root system efficiency factor to compensate for within-layer root system heterogeneities. The performance of this model was tested in an experiment performed in two-compartment split-pot lysimeters with sorghum plants. The compartments were submitted to different irrigation cycles resulting in contrasting water contents over time. The root system efficiency factor was determined to be about 0.05. Release of water from roots to soil was predicted and observed on several occasions during the experiment; however, model predictions suggested root water release to occur more often and at a higher rate than observed. This may be due to not considering internal root system resistances, thus overestimating the ease with which roots can act as conductors of water. Excluding these erroneous predictions from the dataset, statistical indices show model performance to be of good quality.

Simple physics-based models of compensatory plant water uptake: concepts and eco-hydrological consequences

“…The approach gave somewhat better predictions than the empirical Feddes et al (1978) model which does not consider compensatory uptake. More recently, Faria et al (2010) and Casaroli et al (2010) tested the model in experiments with split-compartment lysimeters and pots planted with sorghum and beans. Their results generally validated the overall model concept, but it was shown that ρ i in Eq.…”

“…(2): the phenomenon of hydraulic lift or re-distribution (Dawson, 1993;Caldwell et al, 1998) can be simulated as a source term to the water flow equation, since M i can become smaller than M 0 . However, Faria et al (2010) noted that this model tended to overestimate the quantities of water released by the roots into the soil in their experiments, probably because internal plant resistances are neglected. Uptake compensation is only implicit in the physics-based model described by de Jong van Lier et al (2008) and thus its effects are not at first glance obvious from the equations developed above.…”

“…3, 4 and 11). The values chosen (2, 10, and 50 cm cm −2 , Table 1) were selected to cover most of the range of total live fine root length found among different vegetation types (Jackson et al, 1997), assuming that perhaps up to 10 % of the total fine root length may be effective or active (Faria et al, 2010). With a maximum root depth of 1 m (Table 1), 1 % of the root length is unaccounted for if β is set to 0.955.…”

A new compartmentalised rhizotron system for root phenotyping

“…It should be also recognised that, even though in the present test-trial root drawing was used for RLD estimation, low demanding and automated HD-image acquisition methods could be adapted to this system for more rapid determinations. An innovative aspect of the CRS system, compared to other lab splitroot system used for water uptake partitioning experiment (Faria et al, 2010), hormonal signalling in drought conditions (Saradadevi et al, 2014), or for testing the effects of salinity or soil pollutant (Flores et al, 2002;Langer et al, 2010) is the possibility to create real horizontal layers, independent and variable in height along the soil profile, by positioning a transversal hydrophobic root-permeable film ( Figure 1D) that allows to create different soil moisture/nutrient situations (e.g., a high water table, interchangeable drought soil layers, physical or chemical changes along the soil profile, irrigation with normal or deuterated water, etc.). Therefore, the system offers the possibility to isolate portions of the same root system and evaluate the functioning of specific root traits and segments during plant growth, e.g., deep vs shallow roots, allowing in-deep insights of the dynamic interrelationship of water acquisition in combination with hormonal signalling and/or labelling techniques and canopy water conservation strategies.…”

Horizontal soil water potential heterogeneity: simplifying approaches for crop water dynamics models

“…9a for scenario "maize high T daily on silt loam", the effective values grouped by depth are significantly lower than theoretical values of ρ (blue dotted line), which means that the system behaves as if there were much fewer roots, or maybe, one "big root". This necessity to use smaller values of ρ was already noticed in comparisons with experimental data, by Faria et al (2010), who interpreted that feature as a consequence of rooting heterogeneity, poor contact at soil-root interfaces and inactivity of a significant percentage of roots (approximately 95 %), which thus should not be taken into account when calculating ρ. Through this modelling study, we investigated and confirmed the expected impact of horizontal rooting heterogeneity on ρ.…”