Soil Carbon Storage Under Corn and Switchgrass Grown for Biofuel

This 9 yr field-study, with 3 N-fertility rates, had 2 residue harvesting amounts for corn (Zea Maize) or removal schedules for switchgrass (Panicum virgatum) that were imposed during the final 6 years. The site was near Ithaca, NE on an Aksarben silty clay loam (fine, smectitic, mesic Typic Argiudoll). Soil for chemical and bulk-density measurements were collected from the 0-5, 5-10, and 10-30 cm depths at the beginning of the study and at yrs 3, 6, and 9 by use of a flat-bladed shovel. Following separation of the soil from identifiable plant material, soil organic C was determined using combustion analyses. Depth of soil sampling was a significant source of variation for both the corn and the two switchgrass varieties that were studied. Under corn annual application of 120 kg N/ha resulted in larger amounts of SOC in the 0-5 and 5-10 cm depths, but application of 60 kg N/ha rate resulted in more SOC in the 10-30 cm depth. Corn residue removal decreased total SOC in the 0-5 cm depth. For the ‘Cave-in-Rock' switchgrass variety the 60 kg N/ha resulted in the largest amount of SOC at all 3 depths. Timing of residue removal did not significantly affect SOC within any depth. For the ‘Trailblazer' switchgrass variety the 60 kg N/ha rate resulted in the larger amounts of SOC in the 5-10, and 10-30 cm depths and the August harvest has less SOC than did the October harvest in the 5-10 cm depth. In summary, nitrogen fertilization and sampling depth were important determinants for amount of SOC present at the end of the study, whereas the amount or time of residue removal was less important.