Submitted to: Ecological Society of America Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: August 9, 2002
Publication Date: August 9, 2002
Citation: RUSSELL, A.E., CAMBARDELLA, C.A., LAIRD, D.A., JAYNES, D.B., COLVIN, T.S., MEEK, D.W. NITROGEN FERTILIZER EFFECTS ON SOIL ORGANIC CARBON DYNAMICS IN CORN-SOYBEAN AGROECOSYSTEMS. ECOLOGICAL SOCIETY OF AMERICA PROCEEDINGS. 2002. AVAILABLE FROM: www:esa.org/publications. Technical Abstract: We investigated effects of rate of N fertilization on soil organic carbon dynamics under corn in two Iowa agroecosystems. Our two experimental sites were tilled, tile-drained, corn-soybean rotations in which four-five levels of N, 0-280 kg/ha/yr, had been applied (corn phase only) for five and 22 years. We measured partitioning of corn biomass above and below ground (0-110 cm), tissue chemistry of corn components, total soil organic carbon (TSOC), total soil N, and soil respiration. Total aboveground biomass increased significantly with rate of fertilization, from 797 to 1133 g C/m2. In contrast, root biomass, which comprised <6% of total biomass in these modern hybrids, decreased with increasing N fertilizer, from 49 to 35 g C/m2. Soil respiration was positively correlated with root biomass (r = 0.97), suggesting that soil respiration was driven by root inputs. After 22 years under the experimental fertilization rates, TSOC (0-10 cm) did not differ significantly with N fertilization rate, with late-spring means (SE) ranging from 2506 (39) to 2550 (23) g C/m2 under four N levels. N fertilization is believed to increase TSOC stocks by increasing plant production, hence organic carbon inputs to soils. Our results indicated that under higher N fertilization levels, corn allocated less biomass to roots, leading to lower soil biological activity, hence reduced potential for soil organic carbon accumulation. For these tilled agroecosystems with modern corn hybrids, there was no evidence that N-fertilization rate influenced carbon sequestration.