The Effects of Source, Rate and Placement of Nitrogen and Phosphorus Fertilizers on Growth of Spartina alterniflora Transplants in North Carolina

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Abstract
The effects of rate of N and P fertilizer, type of fertilizer material and application method on establishment, growth and tissue nutrient concentrations of Spartina alterniflora were evaluated on an eroding estuarine shoreline. Both N and P were growth limiting factors at the test site. Biomass increased with increasing rates of N and P up to 224 kg per ha N and 49 kg per ha P when ammonium sulfate and concentrated superphosphate were banded at planting. There were only slight increases in growth when either N or P were applied alone. Placement of fertilizer below ground was necessary; there was no growth response to surface application at transplanting time. The slow-release fertilizers, Mag Amp and Osmocote, supplied N over a longer period of time and produced more growth than the other sources of N which were tested. Urea and urea-formaldehyde were ineffective sources of N. Concentrated superphosphate was as effective as the slow-release fertilizers as a source of P. Nitrogen concentrations in fertilized plants which produced more biomass were lower than in those plants stunted by lack of N or P except where near optimum amounts of N were supplied by the slow-release fertilizers. Residual effects of the fertilizer were evident the second growing season but top-dressing with N and P was necessary to maintain a vigorous stand. Accumulation of up to 28 cm of sand in 2 years was evidence of reduction of shoreline erosion.