Leaching versus input of nitrogen, potassium and magnesium in different fertilizer regimens in Christmas tree stands of Abies nordmanniana in Denmark

The effects of nitrogen (N), potassium (K) and magnesium (Mg) fertilization and deposition on nutrient leaching were assessed in four Danish Nordmann fir Christmas tree stands on former arable land. NPK 23-3-7 fertilizer type was applied in doses between 0 and 1200 kg ha −1 year −1 . Deposition of N, K and Mg varied between 16 and 21 kg N ha −1 year −1 , 2 and 10 kg K ha −1 year −1 , and 2 and 3 kg Mg ha −1 year −1 . The concentration of NO 3 -N in the soil water on the sandy sites was characterized by notable pulses contrasting the mitigated peaks on the clayey site. In general, the soil water concentrations and leaching reflected the fertilization, except for K at one clayey site. Mean annual leaching of NO 3 -N ranged from approximately 6 kg ha −1 year −1 in the control treatment to 235 kg ha −1 year −1 in the 1200 kg ha −1 year −1 fertilizer treatment. In the treatment with the commonly used 300 kg NPK 23-3-7 fertilizer NO 3 -N leaching was estimated to be approximately 46 kg ha −1 year −1 . Annual leaching of N was described in a general model based on the fertilizer input. K and Mg leaching were distinctly more site specific than was N leaching. The magnitude of NO 3 -N leaching caused by application of 300 kg NPK 23-3-7 fertilizer was between the leaching amounts observed in traditional Danish forestry and Danish agriculture.