Nutrient dynamics of Sphagnum farming on rewetted bog grassland in NW Germany.

The agricultural use of drained peatlands leads to huge emissions of greenhouse gases and nutrients. A land-use alternative that allows rewetting of drained peatland while maintaining agricultural production is the cultivation of Sphagnum biomass as a renewable substitute for fossil peat in horticultural growing media (Sphagnum farming). We studied Sphagnum productivity and nutrient dynamics during two years in two Sphagnum farming sites in NW Germany, which were established on drained bog grassland by sod removal, rewetting, and the introduction of Sphagnum fragments in 2011 and 2016, respectively. We found a considerable and homogeneous production of Sphagnum biomass (>3.6 ton DW ha--1 yr-1), attributable to the high nutrient levels, low alkalinity, and even distribution of the irrigation water. The ammonium legacy from former drainage-based agriculture rapidly declined after rewetting, while nutrient mobilization was negligible. CH4 concentrations in the rewetted soil quickly decreased to very low levels. The Sphagnum biomass sequestered high loads of nutrients (46.0 and 47.4 kg N, 3.9 and 4.9 kg P, and 9.8 and 16.1 kg K ha-1 yr-1 in the 7.5 y and 2.5 y old sites, respectively), preventing off-site eutrophication. We conclude that Sphagnum farming as an alternative for drainage-based peatland agriculture may contribute effectively to tackling environmental challenges such as local and regional downstream pollution and global climate change.