Ash fertilization in peatland forest requires water management

Ash fertilization substantially increases stand growth in drained boreal forested peatlands. Growth response lasts  for several decades. Ash fertilization is economically viable management practice and it also can increase ecosystem carbon sink. The long-lasting growth response is a combined result of increased supply of growth limiting phosphorus and potassium, higher soil pH, enhanced microbial activity and nutrient release in soil. An indirect growth response emerges as a feedback from higher foliage mass, increased evapotranspiration and subsequent lower water table and increased organic matter decomposition and nutrient release.  

Previous studies indicate that growth response with respect to unfertilized control is greatest when water table is high. Growth response decreases when water table lowers. In this study, we use Peatland simulator SUSI to search for water management where synergetic benefits from stand growth, ecosystem and soil carbon balance, and nitrogen export to watercourses is achieved. We simulated the combined effects of ash fertilization and water management in Scots pine (Pinus sylvestris L.) stands in different site fertility classes in Southern-Finland, Central-Finland and Northern-Finland. Results indicate that the growth response and effects on carbon balance and nitrogen export are best when water table is maintained high. In intensively drained areas the growth response is small and ash fertilization increases carbon emissions and nitrogen export to water courses.