worm populations

Will Fertilizer Hurt Earthworms? Ammonia and ammonia-based fertilizers can adversely affect earthworms. Annual use of ammonium sulfate, anhydrous ammonia, and sulfur-coated urea has been shown to decrease earthworm populations (Edwards et al., 1995). Is fertilizer safe for worms? Basically, if you add fertilizer of any sort to your soil you will ultimately increase worm populations