# Spectrophotometric Determination of Biopolymers in Alabama Benchmark Soils
###### Abstract  
Biopolymers are organic polymers synthesized by biological organisms. Cellulose, lignin, and proteins are important soil biopolymers known to bind soil particles to improve or strengthen soil structures and support agricultural productivity. In this study, we spectrophotometrically determined the amount of soil cellulose, acetyl bromide lignin, and autoclaved citrate extractable protein in soils in relation to other soil properties. Results showed acetyl bromide lignin > cellulose > autoclaved citrate extractable protein. High clay soils have relatively higher amounts of cellulose and lignin but have lower protein content. The coefficient of variation (CV) of the three biopolymers in the soils studied was autoclaved citrate extractable protein (56.8%), >cellulose (55.2%), >acetyl bromide lignin (44.7%). Pearson correlation analysis showed that soil cellulose was significantly related to cation exchange capacity (CEC), total nitrogen, soil organic matter, and available phosphorus. An increase in soil acetyl bromide lignin suggested an increase in soil organic matter and lower soil available phosphorus. Soil autoclaved citrate extractable protein was significantly correlated with extractable acidity. However, cellulose, acetyl bromide lignin, and autoclaved citrate extractable protein were not significantly correlated with permanganate oxidizable carbon (POxC), electrical conductivity (EC), and C-N ratio. We assume that the concentrations of biopolymers in soils are an intrinsic soil characteristic and contribute to general soil health and productivity. cellulose; acetyl bromide lignin; autoclaved citrate extractable protein; soil organic matter; Alabama soils  
bonds in repeating units of disaccharide cellobiose, with numerous cross-linkages [10]. Cellulose is exclusively a structural polysaccharide with a high tensile strength that makes plants resistant to mechanical stress. Cellulose chains form numerous intra- and intermolecular hydrogen bonds, which account for the formation of rigid, insoluble, crystalline microfibrils that are highly resistant to enzymatic hydrolysis [11]. In soils, cellulose is degraded by cellulase, which is a suite of enzymes with various specificities, working synergistically to degrade this complex polysaccharide [12; 13]. In recent years, there has been growing interest in the use of cellulose and cellulose products in sustainable agriculture systems [14]. Cellulose binds soil particles via hydrogen bonding and its association with clay colloids protects the polymer from degradation. Glacial acetic acid, distilled water, and nitric acid (69%) 8:2:1 (\(v/v/v\)) are used to extract and quantify cellulose in soils. During extraction, the cellulose undergoes acetylosis, with acetic/nitric reagent forming acetylated cellodext, which are dissolved and hydrolyzed to form glucose molecules on treatment with 67-72% H\({}_{2}\)SO\({}_{4}\). The glucose molecules are dehydrated to form hydroxymethyl furfural, which forms a green-colored product with anthrone, the color intensity of which is measured spectrophotometrically between 630 and 690 nm [15]. Lignin is the most abundant biopolymer on earth after cellulose [16]. It is considered a complex heteropolymer consisting primarily of p-hydroxyphenyl, guaiacyl, and syringe units resulting from the oxidative coupling of p-coumaryl, coniferly, and sinapyl alcohols, respectively [17]. The phenolic and aliphatic hydroxyl groups on lignin form H-bonds with hydroxyl and carboxyl groups on clay colloids to give stable soil structures. Lignin is relatively hydrophobic, nontoxic, eco-friendly, and resistant to acid- and base-catalyzed hydrolysis [18; 19; 20]. Studies have shown that lignin-containing compounds coat and bond soil particles to form strong structures [21]. Lignin and lignin-based products have been used to improve soil quality and plant growth [22]. Lignin is extracted from soils with 70% acetone solution in distilled water (\(v/v\)) to remove potential analytical interferences from tannins, flavonoids, and protein.