Improving clay measurement techniques and the prediction of soil behavior for oxidic and volcanic ash soils of Hawaiʻi

Silva, Joshua Hanale Shoichi
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[Honolulu] : [University of Hawaii at Manoa], [August 2013]
Quantifying clay is a fundamental step in predicting and managing soil behaviors such as nutrient and water retention. However, clay measurements are underestimated in soils characterized by oxides and amorphous clay minerals using standard methods. A series of laboratory experiments manipulating dispersant concentration and ultrasonication energy were implemented to improve accuracy of clay measurements in oxidic and volcanic ash soils. A secondary objective explored the use of 1500 kPa water as a potential substitute for clay in predicting soil behavior, and the use of visible near-infrared diffuse reflectance spectroscopy (VNIR-DRS) as a rapid means to predict 1500 kPa water. Increasing ultrasonication energy levels significantly increased measured clay for all oxide and volcanic ash soils, and the response was dependent on soil carbon, oxide content, and surface charge (ΔpH). Microscopy revealed porous sand-sized pumice in some soils, suggesting that conventional particle size analysis may not adequately capture surface area-related behavior. Overall, while 1500 kPa water improved prediction of cation exchange capacity over measured clay in tropical oxidic and volcanic ash soils, the low regression statistics (R2<0.46) indicated that 1500 kPa water is not an appropriate substitute for clay. VNIR-DRS accurately predicted 1500 kPa water, which may be useful in other applications of 1500 kPa water, such as estimating plant available water. While this research demonstrated that clay measurements can be improved by ultrasonication, further research is needed on improving interpretations of measured clay and 1500 kPa water for tropical soils by considering the role other soil factors, like pumice content, surface charge, and organic matter, play on soil behavior.
M.S. University of Hawaii at Manoa 2013.
Includes bibliographical references.
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