Soil carbon fractions in short rotation poplar and black locust coppices, Germany

Short rotation coppice (SRC) is seen as a successful management system, which in addition to energy wood production may enhance soil carbon sequestration. The objective of this study was to investigate total, labile and stable soil carbon fractions at SRCs composed of poplar clones Max 1 (Populus nigra x P. maximowiczii), Muhle Larsen (Populus Trichocarpa), and black locust (Robinia pseudoacacia L.). Study was conducted at three SRC sites (Allendorf, Dornburg, and Forst) varying in age (1-4 years old), soil texture and climatic characteristics, in Germany. Composite soil samples collected at SRCs from 0 to 3; 0-10; 10-30; and 30-60 cm depth layers were compared with soils collected from adjacent crop strips. Samples were analysed for total organic carbon (TOC), hot-water extractable carbon (HWC), and organic carbon (OC) at 250-2,000; 53-250; and < 53 A mu m soil-size aggregates. Total OC stocks in 0-60 cm soil layer were the highest at the site with the heaviest texture, Dornburg, followed by Forst and Allendorf, comprising 92-107; 59-74; and 53-64 Mg ha(-1), respectively. Although no significant differences in the total OC stocks between SRCs and adjacent crops were found for the 0-60 cm layer, a significantly (p < 0.05) higher TOC, HWC, OC at macro-aggregates (250-2,000 A mu m), and the amount of macro-aggregates were found in the top 0-3 cm layer in all SRC sites (except the youngest poplar SRC in Forst) compared to adjacent crop strips. A greater macro-aggregate formation in SRCs related to the lower soil disturbance compared to the tilled crops, revealed a potential of SRC for C sequestration, as C occluded within soil aggregates has a slower decomposition rates and longer residence time.