Fertilization of a low marsh area inhabited by the cord grass,Spartina alterniflora, with inorganic nitrogen and phosphorus compounds was conducted on a monthly basis during the 1972 growing season. Yield of the cord grass, as measured by an increase in fresh weight after its harvest, was significantly higher in the nitrogen fertilized area when compared to the phosphorus fertilized site and a control area. No effect of phosphorus could be demonstrated. It was concluded that nitrogen supplies are limiting production of dwarf formS. alterniflora in the salt marsh under study, and further suggested that introduction of additional sources of inorganic nitrogen into a marsh deficient in nitrogen would tend to increase its productivity.