Carbon and Nitrogen in Danish Forest Soils—Contents and Distribution Determined by Soil Order

Abstract

Increasing atmospheric CO2 concentrations, and widespread deposition of N to terrestrial ecosystems has increased the focus on soil C and N pools. The aim of this study was to estimate the size and distribution of organic C and N pools in well‐drained Danish forest soils. We examined 140 forest soil profiles from pedological surveys of Danish forest soils. We calculated total C and N pools in organic layers and mineral soils to a depth of 1 m. The profiles represent variations in texture (sandy to loamy), and soil order (USDA soil taxonomy Spodosols, Alfisols, Entisols, and Inceptisols). The average total organic C and N contents were 12.5 and 0.61 kg m−2 respectively. There were large differences in total C and N among soil orders. Spodosols had the greatest C content (14.6 kg m−2), and Alfisols the least (8.8 kg m−2), while the N content was highest in Alfisols (0.75 kg m−2) and least in Spodosols (0.51 kg m−2). The main contributor to the high C content in Spodosols is the spodic horizons containing illuvial humus, and thick organic horizons. Carbon and N concentrations decreased with soil depth. Soil clay content was negatively correlated to C content and positively correlated to N content. Soil order and horizon designations may be useful in predicting the total C and N content of Danish forest soils, and may also predict potential for C sequestration following afforestation of arable land.