Reclamation history as explaining factor for soil organic matter content in agricultural landscapes

Reclamation history as explaining factor for soil organic matter content in agricultural landscapes N. Schulp, T. Veldkamp; Wageningen University, Wageningen, The Netherlands. The way a soilscape is managed can have long term effects on size and characteristics of the soil organic carbon (SOC) pool. Because of the often slow response of the SOC pool to changes in input, we hypothesize that land use history, even up to centuries ago, is still reflected in present-day SOC pool variability at landscape level. We tested this hypothesis for a case study in the Dutch cover sand region and evaluated the implications for refining spatial information on SOC pools. The study area was reclaimed from heathlands in several stages between the 17th century and 1950. Land use history was reconstructed from topographic maps from 1850 to 2000 and from land use databases. Soil data was derived from a soil mapping exercise where numerous samples were analysed for organic matter (OM) contents. We used GIS and statistical methods to describe and quantify the effects of land use history, soil classification, groundwater level, elevation and hydrology on OM content. A trend of increasing OM content with increasing reclamation age was found. Especially the oldest reclamations within each soil-groundwater class combination had high OM contents. This relationship is interpreted as the result of the development of socalled plaggen soils in the oldest reclamations, containing high amounts of resistant OM and therefore having large resistant OM pools. Apart from reclamation age, OM content variability can be explained by soil type, groundwater level, distance to the main drainage system and loam content of the soil. We conclude that reclamation age explains part of the variation in OM contents at landscape level. This information about land use history can be useful to refine SOC pool (quantity and quality) mapping efforts at landscape level. Such improved estimates of the SOC pool help to improve estimates of current and future soil carbon balances.