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While improved crop water‐deficit tolerance is considered of primary importance, many phenotyping efforts focusing on quantifying structural root traits make assumptions about architecture representing root function. Therefore, the aim of this study was to quantify whole plant water‐use traits among disparate peanut (Arachis hypogaea L.) genotypes and determine their impact on water‐deficit tolerance. Mini‐rhizotrons were installed to evaluate genotypic root architecture and developmental changes to two irrigation regimes imposed during early development. Following the early‐season irrigation regimes, above‐ and below‐ground traits were studied across a range of soil water conditions through measures of: (a) leaf‐level gas exchange and (b) soil water depletion quantified using a novel soil water probe inserted into mini‐rhizotrons allowing for matched root architecture and soil water depletion measures. While differential water treatments influenced root system architecture development among the genotypes, soil water depletion locations were primarily determined by water availability in the soil profile, not simply by having greater root length at a given soil location. This contradicts the assumption that greater root presence is a consistent indicator of increased root activity. Phenotypic selection of root traits for improving the efficiency of crop water use should consider both structural and functional traits in relation to the intended production environments slated for future cultivar development. [ABSTRACT FROM AUTHOR]