Physical and chemical properties of fen peat soils under agricultural use across Europe.

Peat soils offer numerous functions from the global to the local scale: they constitute the biggest terrestrial carbon storage, form important nutrient filters and provide hydrological buffer capacities. They represent an important share of soils suitable for agriculture in temperate and boreal Europe, pressurized by increasing demands for production. Cultivated peat soils, however, show strong alterations of soil physical and chemical properties, accompanied by extreme mineralization rates, land surface subsidence, soil and water quality deterioration and thus crop failure.The aim of this study is to report soil physical and chemical properties of fen peat soils under typical agricultural management in six European countries in contrast to the technical and economical assessment of the managing farmers. We conducted standardized soil mapping, soil physical/chemical analysis, ground water table monitoring and farm business surveys across 46 sites in Germany, The Netherlands, Denmark, Estonia, Finland and Sweden.The results showed a strong impact of agricultural management on fen peat soil properties across Europe. Peat depth ranged from -0.2 to -4.7 m below ground (on average -1.1 m). The majority of sites were deeply drained, showing annual mean soil water levels of -0.6 m with summer draw downs to -0.93 m. Soil profiles exhibited strong gradients of humification with soil depth, showing fully degraded topsoils (von Post 10 down to -0.2 m), reaching weaker degradation (<= von Post 7) only below -0.6 m. Bulk density, porosity and available field capacity consistently reflected the degradation gradient, whereas hydraulic conductivity and penetration resistance showed no trend. Soil organic carbon was strongly reduced in the topsoil horizons (25% on average) and reached only in horizons below -0.6 m values of on average 45%. Total nitrogen and pH values showed no clear depth gradient. The soil carbon stock ranged from 100 to 500 t/ha for the unsaturated horizons and increases up to 2000 t/ha in the permanently saturated subsoil. The economic relevance of organic soils varied greatly across countries and although farms were settled in organic soil rich regions, 72% of farms had an average share of peat soil of only 23%. The main reasons farmers attributed yield losses on organic soils to were (by importance), high ground water levels, unsuitable water management, and ponding/hydrophobic soils independent of the land use, strongly contrasting the measured water levels. Overall, in the perception of interviewed farmers, the economic success of land use on organic soils in the future will be mostly depended on financial shortcomings due to increasing water logging and inevitably increasing drainage costs agreed on by 65% and 69% of interviewed farmers.