# Spectrophotometric Determination of Biopolymers in Alabama Benchmark Soils
## 4 Discussion
However, lignin was shown to directly increase SAP via competitive P adsorption by the functional groups associated with lignin, rather than by altering soil microbial processes. It has been reported that amending soils with cellulose enhanced plant phosphorus uptake, thus decreasing its amounts in the soils [49]. Our data in this study showed that clay soils with the highest amount of cellulose and AB lignin had the lowest amounts of SAP (Table 2). The acidic sandy soil, Marvyn sandy loam, showed the highest value for SAP, while the alkaline soil, Sumter clay, had the lowest value. Total soil phosphorus exists in both organic and inorganic forms, which are not plant-available [50]. Acid soils are usually high in Fe or Al oxide/hydrous oxides, which immobilize P in the form of FePO4 or AlPO4 compounds, while basic clay soils immobilize or fix P in basic compounds like Ca-phosphates [51; 52]. Phosphorus fixation or immobilization in soils reduces P available to plants. The release of phosphorus from the inorganic pool is extremely slow and occurs when the mineral weathers and dissolves in soil water [53]. Soil microorganisms play a key role in processing and transforming the organic forms of phosphorus into plant-available forms [54]. The strong negative correlations between SAP and soil cellulose and AB lignin indicate that these organic matter fractions may constitute an important P pool easily mineralized to plant-available P under proper soil management practices. Permanganate oxidizable carbon (POxC), also known as active carbon, is used to measure soil carbon changes and is considered the microbially available carbon energy source. Although this study indicated a positive correlation between POxC and overall soil organic matter, there was no significant relationship between POxC and soil cellulose, AB lignin, or ACE protein. Permanganate oxidizable carbon responds better with fresh actively metabolizing organic matter [55] than the relatively stable SOM fractions (soil cellulose, lignin, and protein) in soils under study. While the carbon-to-nitrogen (C:N) ratio is linked to soil organic matter [56], the three soil biopolymers assessed were negatively correlated with C:N ratio, indicating that a high concentration of soil-applied biopolymers may lower the C:N ratio, thus increasing microbial carbon and nitrogen mineralization. Previous studies [29] also showed that soil cellulose and lignin had a weak relationship with the C:N ratio for forest soils. Generally, the higher the soil organic carbon (SOC), the higher the C:N ratio, which promotes microbial immobilization [57]. Lignin and cellulose showed a strong positive correlation with soil organic carbon. The negative correlation between soil biopolymers and C:N ratio may be due to an increase in total nitrogen relative to soil organic carbon. The C:N ratios ranged from 14.4:1 to 7.9:1. Further research is needed to explore the relationship between soil C:N ratio and soil cellulose, AB lignin, and ACE protein. Cellulose and AB lignin showed a strong positive relationship with CEC. The relationships between SC, AB lignin, ACE protein, and CEC were significant, particularly with acidic soils. This is an indication of the significant role these biopolymers may play in retaining cations to support plant growth and development in acidic soils. It is important to note that the soil cellulose, AB lignin, and ACE protein content obtained in this study result from the cumulative decomposition of organic matter. Previous studies have shown that soil organic matter accumulated from crop residues significantly enhanced soil CEC due to the increase in soil negative charges that bind more cations [58]. Cellulose, lignin, and soil protein have ionizable hydroxyl and or carboxyl groups that can provide negative charges on which cations can bind reversibly. The CEC of SCL is much lower than HCL and VCL.