# Spectrophotometric Determination of Biopolymers in Alabama Benchmark Soils
## 2 Materials and Methods
### Soil Analysis  
#### 2.2.1 Spectroscopic Quantification of Biopolymers in Soils  
Extraction and quantification of autoclaved citrate extractable (ACE) soil proteins:  
Proteins were extracted from sieved, well-mixed, air-dried soils, using a modified protocol described by the Cornell University Soil Health Laboratory [26; 27; 28]. In summary, 3.00 g of soil (on an oven-dry basis) were weighed into a pressure- and heat-stable glass screw-top tube, to which was added 24.00 mL of 20 mM sodium citrate buffer (pH 7.00). The mixture (three extractions per soil sample) was shaken to disperse the aggregates and centrifuged at 180 rpm for 5 min to mix well. The tubes were autoclaved for 30 min (121 \({}^{\circ}\)C 15 psi) and then allowed to cool. Two mL of the slurry was withdrawn, added into a smaller microcentrifuge tube, and centrifuged at 10,000\(\times\)\(g\) for 3 min to remove \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Soil Type** & **Soil** & **Taxonomic Class** & **Location** & **Land Use** \\ \hline \multirow{3}{*}{Maryyn sandy loam} & \multirow{3}{*}{MSL} & Fine-loamy, kaolinite, thermic & \multirow{3}{*}{E. V. Smith Research Center, Auburn University} & \multirow{3}{*}{Hayfield fallow.} \\  & & & & \\  & & & & \\ \cline{3-5}  & & & & \\ \cline{3-5}  & & & & \\ \hline \multirow{3}{*}{Altavista silt loam} & \multirow{3}{*}{ASL} & Fine-loamy, mixed, semiactive, thermic & \multirow{3}{*}{E. V. Smith Research Center, Auburn University} & \multirow{3}{*}{Hayfield fallow, previously cropped with winter wheat.} \\  & & & & \\ \cline{3-5}  & & & & \\ \cline{3-5}  & & & & \\ \hline \multirow{3}{*}{Luverne sandy loam} & \multirow{3}{*}{LSL} & Fine, mixed, semiactive, thermic & \multirow{3}{*}{E. V. Smith Research Center, Auburn University} & \multirow{3}{*}{Hayfield fallow.} \\  & & & & \\ \cline{3-5}  & & & & \\ \cline{3-5}  & & & & \\ \cline{3-5}  & & & & \\ \hline \multirow{3}{*}{Compass loamy sand} & \multirow{3}{*}{CLS} & Coarse-loamy, siliceous, sub-active, thermic & \multirow{3}{*}{E. V. Smith Research Center, Auburn University} & \multirow{3}{*}{Hayfield fallow.} \\  & & & & \\ \cline{3-5}  & & & & \\ \cline{3-5}  & & & & \\ \cline{3-5}  & & & & \\ \hline \multirow{3}{*}{Decatur silt loam} & \multirow{3}{*}{DSL} & Fine, kaolinite, thermic & \multirow{3}{*}{Winfred Thomas Agricultural Research Station, Alabama A\&M} & \multirow{3}{*}{Left fallow for more than 15 years.} \\  & & & & \\ \cline{3-5}  & & & & \\ \cline{3-5}  & & & & \\ \cline{3-5}  & & & & \\ \hline \multirow{3}{*}{Cahaba sandy loam} & \multirow{3}{*}{CSL} & Fine-loamy, siliceous, semiactive, thermic & \multirow{3}{*}{E. V. Smith Research Center, Auburn University} & \multirow{3}{*}{Hayfield fallow, previously cropped with soybean.} \\  & & & & \\ \cline{3-5}  & & & & \\ \cline{3-5}  & & & & \\ \hline \multirow{3}{*}{Houston Clay} & \multirow{3}{*}{HCL} & Very fine, smectite, thermic & \multirow{3}{*}{Blackbelt Research and Extension Center, Auburn University} & \multirow{3}{*}{Hayfield fallow.} \\  & & & & \\ \cline{3-5}  & & & & \\ \cline{3-5}  & & & & \\ \cline{3-5}  & & & & \\ \hline \multirow{3}{*}{Vaiden Clay} & \multirow{3}{*}{VCL} & Very fine, smectite, thermic & \multirow{3}{*}{Blackbelt Research and Extension Center, Auburn University} & \multirow{3}{*}{Hayfield fallow} \\  & & & & \\ \cline{3-5}  & & & & \\ \cline{3-5}  & & & & \\ \cline{3-5}  & & & & \\ \hline \multirow{3}{*}{Sumter Clay} & \multirow{3}{*}{SCL} & Fine-silty, carbonate, thermic & \multirow{3}{*}{Blackbelt Research and Extension Center, Auburn University} & \multirow{3}{*}{Hayfield fallow.} \\  & & & & \\ \cline{3-5}  & & & & \\ \cline{3-5}  & & & & \\ \cline{3-5}  & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Taxonomic class of soils used. soil particles. Twenty-five (25) \(\upmu\)L of the cleared sample extract was added to 200 \(\upmu\)L of bicinchoninic acid (BCA) reagent in the well of a 96-well plate, giving a BCA working solution: sample ratio of 8:1.