Total and available soil carbon fractions under the perennial grass Cynodon dactylon (L.) Pers and the bioenergy crop Arundo donax L

Understanding and quantifying the impact of bioenergy crops on soil carbon (C) storage is an essential component of crop management. Our objectives were to (i) compare total (TC), organic (OC), and inorganic carbon (IC) storage under Cynodon dactylon (L.) Pers and the energy crop Arundo donax L. along the soil profile, and (ii) determine the effect of these crops on available soil C (measured as hot water extractable C, HC) as an indirect indicator of soil C changes. The study site was within the Rio Grande floodplain in Quemado, Texas covered by A. donax and C. dactylon. Soil samples were taken from five soil depths: 0-10, 10-20, 20-30, 30-40, and 40-50 cm at 125 locations in a 34.5 ha field; TC, IC, and HC were measured and OC was derived. In all four C pools, soils under A. donax had higher C content (volumetric C or Cv, kg m ^-2) than soils under C. dactylon, except for IC at the top two depths. Larger soil C storage under A. donax as compared to C. dactylon was consistent throughout the profile. The effect was most pronounced for volumetric HC content (HCv) with 43% higher amount under A. donax than C. dactylon at 0-10 cm depth. In areas, where A. donax is considered an invasive species, the available biomass can be used for bioenergy production and the higher soil carbon under A. donax can provide additional economic return in a C economy.