Soil scientists have been using the same quantification methods for soluble salts for
decades. Yet they have long struggled with an effective method for quantifying gypsum content,
because current methods are fraught with problems. Saline soil has been historically defined as soil containing salts more soluble than gypsum (e.g., various combinations of Na+, Mg2+, Ca2+, K+, Cl-, SO42-, HCO3- and CO32-) to the extent that soil fertility is severely reduced across a wide array of climates and geological settings. Since salinity is not germane to specific soil characteristics such as texture or parent material, it can be challenging to predict salt concentrations within a profile. Given the success of previous studies using portable x-ray fluorescence (PXRF) as a tool for measuring soil characteristics, the evaluation of soluble salts in soil with PXRF seems timely. Not only does this newer technology offer more accurate, quantifiable data to investigators, it produces results in-situ, in seconds. Recent enhancements to PXRF spectrometers have provided better detection limits especially for lighter elements such as S and Cl, a key component of gypsum and other salts. Thus, this research aimed to test the effectiveness of PXRF as a means of directly quantifying gypsum and salinity in soils. A total of 102 soil samples containing a wide variety of gypsum (~295%) and 122 samples with various salt concentrations were subjected to both traditional laboratory analysis (thermogravimetry and electrical conductivity, respectively) and elemental analysis via PXRF. Simple and multiple linear regression were used to establish the relationship between the two data sets. Log transformation of some data sets was necessary to normalize the data. Using simple linear regression between laboratory and PXRF data, an R2 of 0.88 was produced for the gypsum data, and an R2 of 0.839 was produced for salinity data. Similarly, simple linear regression for laboratory-quantified gypsum vs. PXRF S produced an R2 of 0.91. Multiple linear regression of laboratory quantified gypsum vs. both PXRF S and Ca produced an R2 of 0.91, and 0.8669 for laboratory determined EC (dS m-1) vs. PXRF Cl, S, Ca, and K. No significant differences were observed between model generation and validation data sets. Overall, PXRF shows great promise for the direct quantification of soluble salts in soils.
| Identifer | oai:union.ndltd.org:LSU/oai:etd.lsu.edu:etd-11182013-111230 |
| Date | 22 November 2013 |
| Creators | Swanhart, Samantha Lynn |
| Contributors | Tubana, Brenda, Walsh, Maud, Weindorf, David |
| Publisher | LSU |
| Source Sets | Louisiana State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lsu.edu/docs/available/etd-11182013-111230/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached herein a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to LSU or its agents the non-exclusive license to archive and make accessible, under the conditions specified below and in appropriate University policies, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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