Development and Characterization of Lignin‐Based Hydrogel for Use in Agricultural Soils: Preliminary Evidence

Abstract

In arid and semi‐arid regions of the world, agricultural production is greatly limited by water scarcity and inefficient water use. Water‐absorbent hydrogels are a technological solution that can retain soil water for plants. A lignin‐based hydrogel as a natural plant‐based water absorbent is prepared from lignin alkali polymers and poly(ethylene glycol) diglycidyl ether (PEGDGE) in adjusted alkali (NaOH) solution. The maximum swelling capacity of the hydrogel is achieved in 1.5 m NaOH with 0.5 mmol PEGDGE g lignin −1. Water swelling capacity is 34 g g Hydrogel −1 dry weight of hydrogel in distilled water, which is reduced to 53% and 64% in 0.1 m NaCl and 0.1 m CaCl2 solution, respectively. Biodegradability and phytotoxicity tests show that 6.5% of the sample mass decomposed after 40 days of incubation in soil solution media and the hydrogel is not phytotoxic to wheat seeds. These findings support the use of the lignin‐based hydrogel as an environmentally friendly additive to promote water retention in dry, saline soils. Due to the limitations of this study, further assessments are needed in order to understand the efficiency of lignin‐based hydrogel application in different soils with different biota.

Biodegradability of bio‐based and synthetic hydrogels as sustainable soil amendments: A review

“…Here, a supernatant solution is extracted from a soil sample and either inoculated with specific microbial species, 25,29,30 and the hydrogel sample is incubated in the inoculum in a controlled environment, or native microbial species present in the soil supernatant serves as the degrading microbial species. 31 In the soil burial test, the extent of biodegradation is determined by measuring the weight loss in the hydrogel, which is assumed to represent the percentage of biodegradation in soil. 28,[32][33][34] In the case of the supernatant incubation method, the extent of biodegradation is determined by either weight loss, 31,35 through structural, morphological examination using a scanning electron microscope, 26,36 or through quantifying the CO 2 mineralization using a gas chromatograph or other measuring equipment.…”

“…31 In the soil burial test, the extent of biodegradation is determined by measuring the weight loss in the hydrogel, which is assumed to represent the percentage of biodegradation in soil. 28,[32][33][34] In the case of the supernatant incubation method, the extent of biodegradation is determined by either weight loss, 31,35 through structural, morphological examination using a scanning electron microscope, 26,36 or through quantifying the CO 2 mineralization using a gas chromatograph or other measuring equipment. 35,37,38 While the soil burial and weight loss method are commonly used in literature, this method has some limitations.…”

“…Alternatively, biodegradation is tested using the supernatant incubation method. Here, a supernatant solution is extracted from a soil sample and either inoculated with specific microbial species, 25,29,30 and the hydrogel sample is incubated in the inoculum in a controlled environment, or native microbial species present in the soil supernatant serves as the degrading microbial species 31 . In the soil burial test, the extent of biodegradation is determined by measuring the weight loss in the hydrogel, which is assumed to represent the percentage of biodegradation in soil 28,32–34 .…”

“…Lignin, which forms one of the main components of lignocellulosic plants and is the second most abundant plant polymer after cellulose 65 has been successfully used to synthesize biodegradable hydrogels. Mazloom et al 31 synthesized a lignin hydrogel and tested its biodegradation rate. In their study, the microbial inoculum for biodegradation was extracted from dry soil through centrifugation.…”

Significance of biopolymer-based hydrogels and their applications in agriculture: a review in perspective of synthesis and their degree of swelling for water holding

“…This hydrogel proved to be an effective material to be used for plants under water stress conditions. 66 Another method proposed for the synthesis of lignin hydrogel includes the use of waste from the pulp and paper industry by a co-polymerization technique using acrylic acid and red liquor (industrial waste). This hydrogel was not only cost-effective but is also very environmentally friendly as it is biodegradable and reduces waste pollution.…”