A liquid fertilizer is produced from off-gassed ammonia resulting from the processing of animal waste materials, particular animal manure. The vaporized ammonia is generated primarily by heating the animal waste materials and capturing the resulting vapors and particulate materials. The ammonia vapors and particles are removed from the gas stream through a scrubbing operation, which creates an ammonium-enriched liquid stream that can be concentrated into an organic fertilizer having a high-nitrogen content.