Soil organic C and N stocks in the first rotation of poplar plantations in Germany

Abstract

Short rotation coppices (SRC) have the potential to sequester soil organic carbon (SOC), although the magnitude differs depending on soil properties and former land use. At 20 sites recently transformed to poplar SRC, the legacy effects of former land use on SOC and total nitrogen (N) stocks were investigated down to 90 cm depth in relation to the effects of soil properties and climatic variables. Microbial biomass C (MBC), aggregate size classes, and light fraction (LF) particulate organic matter (POM) were tested as indices for the effect of former land use. SOC stocks ranged from 38 to 229 t ha−1 and total N stocks from 3.2 to 14.8 t ha−1. SOC stocks were lowest in former arable soils (74 t ha−1) and highest in former plantation soils (151 t ha−1). Increasing clay content usually had positive effects on SOC and total N stocks in topsoils (0–30 cm) and subsoils (30–90 cm), except in plantation topsoils, whereas effects of increasing soil pH were only positive at the grassland sites. Increased mean annual temperature generally had negative effects on SOC and total N stocks in topsoils, but positive effects on grassland and plantation subsoils. Increased mean annual precipitation generally had positive effects on SOC stocks at grassland and plantation sites, but only small effects at arable sites. The same was true for total N stocks, except for the negative effects in the plantation subsoils. MBC was closely related to SOC at 0–30 cm depth. Water stable macro- (250–2000 μm) and microaggregates (53–250 μm) as well as the silt + clay fraction (< 53 μm), free LF-POM, and occluded LF-POM were not affected by former land use in topsoils, due to strong variation between replicate cores.