Briquetted fertilizer for forest fertilization

A briquetted fertilizer for forest fertilization having a volume of from 5 to 100 cm.sup.3, a shape retention time in water of over one year, active as a fertilizer for at least about three years after application and which consists essentially of a compression molded mixture of granular isobutylidene diurea having a water content of from 1 to 15 percent, 1 to 5 percent by weight of a heavy mineral oil as an unencapsulating or randomly mixed binder and up to 30 percent by weight of at least one member selected from the group consisting of water insoluble or 2 percent citrate soluble calcined phosphate, fused phosphate, phosphate rock and gradually efficacious potassium phosphate.