Author (Your Name)

Alicia FischerFollow

Date of Award


Document Type

Honors Thesis (Open Access)


Colby College. Geology Dept.


Dr. Robert Gastaldo

Second Advisor

Dr. Craig Rasmussen

Third Advisor

Dr. Tasha Dunn


Calcic soil horizons are significant carbon sinks. Yet, despite their abundance in semiarid environments, calcic soils are enigmatic for two reasons: (1) some authors hypothesize that dust input does not, independently, control the geochemical properties of these soils; and (2) few studies have examined how these calcic soils change geochemically with respect to irrigation. A 2017 pilot study used portable x-ray fluorescence (pXRF) on calcic soils in Southeastern Arizona (SEAZ) to address these questions. However, this technology has not been widely employed to evaluate soils. The current study addresses whether pXRF and XRF data obtained from the same soil samples are comparable. As such, calcic soils sourced from basalt, rhyolite/andesite, limestone, and mixed alluvium were collected from SEAZ and analyzed using pXRF and XRF. Analysis revealed that pXRF obtained significantly lower elemental values compared to XRF, indicating that one must exert caution when using pXRF analyses on soils. The XRF data show that there are clear geochemical differences between the calcic horizons originating on different parent materials, which suggests that dust input does not, solely, control the calcium input into these soils. And, the geochemical composition of sprinkler-irrigated mineral A-horizons of soil does differ from non-irrigated soil, which indicates that high-volume water input (>240 gallons/hour) is needed to alter the soil composition. Yet, irrigation over 100 years has not completely changed the calcic soil composition. Thus, a longer time of irrigation (greater than 100 years) is needed to potentially initiate the release of carbon sequestered in these calcic soils.


Calcic, soil, Tucson, irrigation, A-horizon

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Fischer - Honors Thesis Appendix.xlsx (44 kB)

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