Abstract: The invention relates to a long-acting phosphorus fertilizer that contains a phosphorus source and an iron source, at least 10% by weight of the phosphorus present in the phosphorus fertilizer being insoluble in water but soluble in neutral ammonium citrate, the phosphorus fertilized being in the form of granules or pellets. The invention additionally relates to a method for fertilizing acid, iron-poor forest soils, wherein a phosphorus fertilizer such as this is spread on the forest soil to be fertilized, the iron present in the fertilizer preventing the phosphorus from being leached out, centrifugal distribution being preferably used.