Date of Award:

5-2013

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Committee Chair(s)

Astrid R. Jacobsen (Committee Co-Chair), Grant E. Cardon (Committee Co-Chair)

Committee

Astrid R. Jacobsen

Committee

Grant E. Cardon

Committee

Janis L. Boettinger

Committee

Scott B. Jones

Committee

Paul R. Grossl

Committee

Jürgen Symanzik

Abstract

High amounts of salts in soils and a greater tendency of these soils to become even more saline is of great concern in arid and semi-arid western United States. Soils in Cache County, Utah are no exception. Salinization negatively affects the soil, crop, and the quality of groundwater. Thus, the long-term sustainable management of irrigated agricultural lands is threatened.

However, the salinity of these soils are closely monitored and managed to ensure sustainable agricultural productivity. A widely accepted and traditional standard method for estimating soil salinity is by measuring electrical conductivity of saturated paste extracts. Apart from the tedious and time-consuming nature of this method for detailed salinity inventory, it underestimates salinity due to a chemical artifact referred to as ion pair formation in high ionic strength solution.

The purpose of this research is to evaluate the utility of an electromagnetic induction sensing to understand the dynamics and interacting factors controlling soil salinity. With the electromagnetic induction technique, salinity can be monitored rapidly and non-destructively. However, electromagnetic induction measurements must be calibrated to measure salinity. The challenge in calibration is because the sensor estimates other properties of the soil in addition to salinity. Previous studies assumed uniformity of all soil properties, except soil salinity, influencing the sensor reading. Such homogeneous conditions rarely occur in soil.

Checksum

549cf21f3fc71c1dc424c90615ef0b34

Comments

Soil salinization is of great concern in the irrigated arid and semi-arid western United States due to its threat to sustainable agricultural productivity and thus is closely monitored. A widely accepted and traditional standard method for estimating soil salinity is the electrical conductivity of the saturated paste extracts (ECe). However, this method underestimates salinity due to ion pair formation in high ionic strength solution. Numerous studies have recommended the use of an electromagnetic induction (EMI) sensing technique to monitor field-scale soil salinity due to rapidness and non-destructiveness of the sampling. However, because the EMI measurement (ECa) is related to a host of soil properties, calibrating ECa to salinity in a non-homogeneous setting is particularly challenging. The main objective of this study is to understand the dynamics and interacting factors controlling soil salinity using an EMI sensor. Specifically, a correction is made for the underestimation of soil salinity from saturated paste extracts, and a calibration model is developed that is capable of predicting salinity directly from ECa despite the non-homogeneity of potential perturbing factors. A comparison is made of salinity measurement methods based on soil saturated pastes with respect to specific soil management goals. Results show that ion pairing exists even in low ionic strength solution and by diluting the saturated paste extracts to conductivities ≤ 0.03 dS m -1 (ECed), ion pairing is minimized. An improved salinity estimate is obtained by computing total dissolved solids (TDS, in mM) from the ECed values, and then multiplying the TDS by the dilution factor. We also developed a calibration model using quantile regression, which makes no assumption about the distribution of the errors, and which is capable of predicting low range soil salinity (such as that in calcareous soils) from ECa depth-weighted measurements (ECH25ECe). A comparison of ECe, ECed, ECH25ECe, and direct measurement of EC in soil pastes (“ Bureau of Soils Cup ” method, ECcup) across six depths, three texture groups, and the combinations of EC method and depth or texture groups, supports the use of the ECH25ECe method to rapidly and reliably monitor salinity in calcareous soils of arid and semiarid regions.

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