Determining the Effect of a Potential Biofuel Crop On Soil Carbon Forms and Their Determination Using VisNIR Spectroscopy.

Understanding and quantifying the impact of biofuel crops on soil carbon storage is an essential component of sustainable cultivation of these crops. Research is also needed to develop rapid and inexpensive techniques of carbon estimation.Our objectives were to compare soil carbon storage of a biofuel crop, Arundo (Arundo Donax L), with Coastal Bermuda grass (Cynodon dactylon (L.) Pers), and to evaluate the potential of proximal visible/near infrared diffuse reflectance spectroscopy (VisNIR-DRS) to estimate total and available carbon. Measurement of available carbon can help in identifying short-term changes in soil carbon, while VNIR-DRS can offer a cost-effective alternative for predicting available carbon. The study site was within the Rio Grande floodplain in Quemado, Texas with mixed acreage of Arundo and Bermuda grass. Soil samples were taken from five soil depths; 0 to 10, 10 to 20, 20 to 30, 30 to 40, and 40 to 50 cm. Total (dry combustion), inorganic (modified pressure calcimeter), and hot water extractable carbon (TC, IC and HC) were measured and organic carbon (OC) was calculated by difference in TC and IC. The difference between crops and soil carbon storage by depth were compared using the Kruskall Wallis test. Proximal VisNIR-DRS scans of dried ground soil were used to predict TC and HC using Partial Least Squares regression. For all four carbon pools, soils with Arundo had higher carbon concentration than soils with Bermuda grass, but the effect was most pronounced for HC (79 % greater at 0 to 10 cm depth). Larger soil carbon values with Arundo were consistent throughout the profile, but the effect diminished with increasing depth. All four carbon pools were predicted using VisNIR-DRS (R² > 0.88, RMSE 0.20-5.53). In conclusion, Arundo showed a significant potential for soil carbon sequestration and VisNIR-DRS showed potential for estimating carbon, including available carbon.