Status of plant-available potassium after 17 years of wet grassland restoration on a degraded minerotrophic peat soil

Potassium availability is an important regulator of plant species composition and ecosystem productivity. Hence, potassium plays a crucial role when the aim is to produce notable quantities of roughage in wet grassland farming. The objective of this case study was to elucidate the long-term dynamics of plant-available potassium (K-DL) in a seasonally rewetted peatland in the Dummer lowland in northwest Germany. This study investigated the effects of three grassland management systems and the impact of greatly fluctuating water levels on the K-DL content. Over a period of 17 years, four sampling campaigns were conducted across the study area. The most remarkable result was that strong discontinuous nutrient dynamics were observed over time. In the early years, the varying nutrient pathways of the three grassland systems significantly determined K-DL content. Over time, the grassland effects decreased, while the effect of seasonal rewetting on K dynamics increased. After 17 years, all the grassland systems showed a similar very high K-DL content. This was probably due to a periodical recharge of the K-DL stocks by seasonal inundation events. Therefore, successful nutrient management should consider specific land-use effects as well as the heterogeneous dynamics and water quality of seasonal flooding events.