Abstract
The geometry of rooting systems is important for modeling water flows in the soil-plant-atmosphere continuum. Measured information about root density can be summarized in adjustable equations applied in hydrological models. We present such descriptive functions used to model root density distribution over depth and evaluate their quality of fit to measured crop root density profiles retrieved from the literature. An equation is presented to calculate the mean root half-distance as a function of depth from root length density profiles as used in single root models for water uptake. To assess the importance of the shape of the root length density profile in hydrological modeling, the sensitivity of actual transpiration predictions of a hydrological model to the shape of root length density profiles is analyzed using 38 years of meteorological data from Southeast Brazil. The cumulative root density distributions covering the most important agricultural crops (in terms of area) were found to be well described by the logistic function or the Gompertz function. Root length density distribution has a consistent effect on relative transpiration, hence on relative yield, but the common approach to predict transpiration reduction and irrigation requirement from soil water storage or average water content is shown to be only partially supported by simulation results.
Highlights
The quantitative description of the spatial distribution of the root system in the soil profile is an important topic for the modeling of water and solute uptake patterns by roots in the soil-plant-atmosphere continuum at several scales [1,2]
We tested the quality of fit of some descriptive functions used to simulate root length density distribution over depth by fitting to experimentally established crop root density profiles retrieved from literature
We assessed the importance of the shape of the root length density profile in hydrological modeling by testing the sensitivity of actual transpiration predictions to shape parameters of root length density functions
Summary
The quantitative description of the spatial distribution of the root system in the soil profile is an important topic for the modeling of water and solute uptake patterns by roots in the soil-plant-atmosphere continuum at several scales [1,2]. Radiation balances, and to a lesser degree, precipitation patterns, appear to be sensitive to rooting distribution patterns [3,4,5]. Some research, such as [6], has attempted to present root profile parameters for specific vegetation types to be used in these models. The fact that root water uptake is closely related to biomass production [11] is at the core of ecological and agricultural analyses of water-limited growth and water use efficiency
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