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Spectral indices (SI) derived from crop reflectance data are sensitive to chlorophyll a and b content (Chl). However, the SI--Chl relationship might be confounded by variation in leaf area index (LAI) and soil background reflectance, especially in semiarid environments where water determines crop growth. This study evaluated the sensitivity of SI to variation in soil reflectance and how this may affect overall SI performance for ground-based sensing of Chl in dryland wheat (Triticum aestivum L.). Selected SI were computed from spectra simulated by the PROSPECT-SAIL radiative-transfer model for 5 LAI values, 7 Chl values, and 121 dry soil surface reflectance spectra. These spectra represented soils across major wheat growing areas in the United States. Soil properties and reflectance varied widely among the soils indicated by the high SI variation for LAI values < 1.5. Overall, soil background variation contributed less to the observed SI variability ( Abbreviations: Chl, chlorophyll a and b content; GESAVI, Generalized soil adjusted vegetation index; LAI, leaf area index; MCARI, modified chlorophyll absorption in reflective index; NDRE, normalized difference red edge index; NDVI, normalized difference vegetation index; OSAVI, optimized soil adjusted vegetation index; SAVI, Soil Adjusted Vegetation Index; SI spectral index; MTV2, Second Modified Triangular Vegetation Index; TCARI, transformed chlorophyll absorption in reflectance index; TSAVI, Transformed Soil Adjusted Vegetation Index.