Flux-based plant water availability in tropical soils from Brazil

Abstract

Traditionally, total available water (TAW) is defined as the difference between the water content at field capacity (FC) and wilting point (WP), while readily available water (RAW) is the water content between FC and the limiting point (LP). Accurate estimation of FC, LP, and WP remains challenging due to their dependence on soil, plant, and atmospheric interactions and has advanced by process-based approaches. However, the lack of comprehensive soil hydraulic data limits the application of such methods, particularly in tropical regions. This study addresses this gap by conducting a detailed hydraulic characterization of twenty tropical soils from southeast Brazil. Using a flux-based approach, TAW and RAW were evaluated within the context of soil water balance simulations under a local climate and cropping scenario in a stochastic framework. The findings highlight the importance of process-based methods and quality soil data, and allow to conclude that flux-based predictions of TAW and RAW should be preferred, as they correlated better to soil water balance components. It was shown that median values from stochastic simulations of characteristic water contents and soil water balance components can differ significantly from deterministic simulation results. A stronger alignment of the flux-based method with soil water balance components was shown in comparison to the traditional (static) method. Disadvantages of the flux-based method include the greater need for detailed soil information (full soil hydraulic properties) and an increased computational effort. Flux-based field capacity medians corresponded to pF-values between 1.5 and 2.3, limiting points ranged from 2.0 to 3.9, and wilting points varied between 3.2 and 4.3. Median TAW values ranged from 0.05 to 0.19 cm3 cm−3, while RAW ranged from 0 to 0.12 cm3 cm−3. The results highlight the importance of detailed soil hydraulic data and process-based modeling, allowing for improved predictions of plant water availability and water management.