Intra-annual changes in biomass, carbon, and nitrogen dynamics at 4-year old switchgrass field trials in west Tennessee, USA

Switchgrass is a potential bioenergy crop that could promote soil C Sequestration in some environments. We compared four switchgrass cultivars on a well-drained Alfisol to test for differences in biomass, C, and N dynamics during the fourth growing season. There was no difference (P > 0.05) among cultivars and no significant cultivar x time interaction in analyses of dry mass, C stocks, or N stocks in aboveground biomass and surface litter. At the end of the growing season, mean (+/-SE) aboveground biomass was 2.1 +/- 0.13 kg m(-2), and surface litter dry mass was approximately 50% of aboveground biomass. Prior to harvest, the live root:shoot biomass ratio was 0.77. There was no difference (P > 0.05) among cultivars for total biomass. C, and N stocks belowground. Total belowground biomass (90 cm soil depth) as well as coarse (>= 1 mm diameter) and fine (<1 mm diameter) live root biomass increased from April to October. Dead roots were <10% of live root biomass to a depth of 90 cm. Net product ion of total belowground biomass (505 +/- 132 g m(-2)) Occurred in the last half of the growing season. The increase in total live belowground biomass (426 +/- 139 g m(-2)) Was more or less evenly divided among rhizomes, coarse, and fine roots. The N budget for annual switchgrass production was closely balanced with 6.3 g N m(-2) removed by harvest of aboveground biomass and 6.7 g N m(-2) supplied by fertilization. At the location of our study in west Tennessee, intra-annual changes in biomass, C, and N stocks belowground were potentially important to crop management for soil C sequestration. (C) 2010 Elsevier B.V. All rights reserved.