Perennial agricultural crops produced for biofuel have the potential to act as a carbon sink if root derived C is stabilized in the soil below the plow layer. The quantity of roots, their distribution with depth, and the allocation of carbon to exudates and mycorrhizal symbionts are all ways in which carbon is delivered to the soil system. Despite the importance of root-derived C inputs to the soil, roots are understudied and not well-understood in Miscanthus x giganteus (Miscanthus), a potential source of cellulosic-based biofuel in the future. Unlike other grass bioenergy crops, Miscanthus is perennial and therefore age effects may be important to quantify. To begin quantifying belowground carbon sink potential in Miscanthus, fine root density (FRD) was quantified in an Iowa trial where soil cores to a depth of 1m were extracted at depth increments of 0-10 cm, 10-20cm, 20-30cm, 30-50cm, and 50-95.5 +/- 10 cm. Data were analyzed with respect to crop age (1, 2, and 3 year old plantations), and fertilization rates of 0, 90, 178, 268, 357 kg N/ha. Ultimately, the response of roots to fertilization over time will influence if Miscanthus has potential to be a sustainable renewable fuel source.
Results/Conclusions
Significant differences in FRD existed at each depth increment in the soil (p<0.05). The top 10 cm of soil contained the greatest FRD (1.77 +/- 0.15 mg/cm3), followed by the 10-20 cm, 20-30 cm, 30-50 cm, and 50-100 cm depth intervals (0.84 +/- 0.70, 0.50 +/- 0.04, 0.31 +/- 0.20, and 0.19 +/- 0.02 mg/cm3, respectively). There was a significant effect of crop age on FRD (P<0.05). FRD was greatest in three-year-old plots (0.93 +/- 0.11 mg/cm3), intermediate in the 1-year-old plots (0.68 +/- 0.08 mg/cm3) and lowest in the 2-year-old plots (0.58 +/- 0.05 mg/cm3). Fertilization significantly (P<0.05) reduced FRD. Under control conditions FRD (0.97 +/- 0.14) was greater than all the other fertilization rates (averaging 0.68 +/- 0.05). Our results indicate root-derived C sequestration significantly decreases with the use of fertilization, but post-hoc analyses revealed fertilization did not affect FRD below the plow layer (<30 cm) and did not effect 3-year-old plots. Our results also indicate that root-derived C does not necessarily increase with age in Miscanthus.