A method for producing a poultry litter-based fertilizer by a) supplying poultry litter to a rotating rotary drum, b) adding acid or a source of acid to the rotating rotary drum, wherein acid reacts with the poultry litter to form an acidified mixture, c) adding ammonia or a source of ammonia to the rotating rotary drum, d) drying and cooling the ammoniated product by evaporation of water to form a dried, cooled product in a free-flowing semi-solid or solid form, repeating the steps b) through d) until a desired nitrogen content is reached in the poultry litter-based fertilizer.