Abstract
Superabsorbent polymers (hydrogels) have been proposed as soil amendments to increase the amount of plantavailable water in the soil. Synthetic hydrogels have been widely investigated for use in agriculture. Due to increasing environmental concerns related to synthetic hydrogels, naturally sourced hydrogels are of interest because of their potential for increased biodegradability and biocompatibility. A lignin-based hydrogel was synthesized for this study, and its swelling properties and water absorption capacity were determined. The hydrogel was characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and gas pycnometry. A hanging water column, pressure plate apparatus, and dew point potentiometer were used to measure the soil water retention curve from saturation to ovendryness for silt loam and loamy fine sand soils after amendment with the lignin-based hydrogel. Results showed a maximum swelling ratio in deionized water of 2013% of the hydrogel's original mass, 1092% in tap water, and 825% in a 0.9% NaCl solution. The FTIR spectra of the hydrogel showed the presence of O-H bonds from the lignin structure, which renders the hydrogel reactive to a crosslinker and forms insoluble bonds, thereby allowing the hydrogel to swell when exposed to water. SEM images of the lignin hydrogels indicate large macropores, which allowed for water absorption. Applying hydrogels significantly increased the soil's water-holding capacity at 0.3% (w/w) treatment. Hydrogel treatment significantly increased water retention at saturation or near saturation by 0.12 cm3 cm-3 and at field capacity by 0.08 cm3 cm-3 for silt loam soil at 1% (w/w) treatment compared to the control treatment with no added lignin hydrogel. Hydrogel application increased water retention over the range of the soil water retention curve from -3 to -15,000 cm for the loamy fine sand soil at 1% (w/w) treatment. However, the application of lignin-based hydrogel did not affect plant available water capacity (PAWC) in either soil tested. These results serve as preliminary evidence upon which further lignin-based hydrogel amendment studies could be built by testing higher concentrations of hydrogel in the soil.
Original language | English |
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Pages (from-to) | 85-98 |
Number of pages | 14 |
Journal | Journal of the ASABE |
Volume | 66 |
Issue number | 1 |
DOIs | |
State | Published - 2023 |
Bibliographical note
Funding Information:This work is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, Hatch-Multistate under grants 1002344 and 1003563. Co-author O.W. acknowledges support for this work through the KY006120 Hatch/Multistate Project "Soil, Water, and Environmental Physics to Sustain Agriculture and Natural Resources." Thanks to Dr. Akinbode Adedeji for his support with gas pycnometry. The authors thank Udari Shyamika and Dr. Doo Young Kim from the Department of Chemistry, University of Kentucky, for their support with FTIR data collection. We thank Diane Hunter of the University of Kentucky Division of Regulatory Services for her assistance with soil analysis. The authors appreciate Tim Smith's assistance with the construction of soil collars. The authors also thank Emily Nottingham and Dr. Tiffany Messer for their assistance with electrical conductivity measurements.
Publisher Copyright:
© 2023 American Society of Agricultural and Biological Engineers.
Keywords
- Lignin
- Soil water retention curve
- Super absorbent polymers
- Swelling capacity
- Water retention
ASJC Scopus subject areas
- Agronomy and Crop Science
- Food Science
- Forestry
- Soil Science
- Biomedical Engineering