In 1972, an experiment was established adjacent to another tidal 

 creek in the same marsh to evaluate the effect of phosphorus fertiliza- 

 tion. The experiment was a factorial design with two levels of phosphorus 

 and four levels of nitrogen identical to the factorial experiment previous- 

 ly described for Ocracoke. Three randomized complete blocks were esta- 

 blished with the individual plots perpendicular to a creek so that each 

 plot contained the tall and short forms of grass. Plots were 1.22 by 

 15.2 meters with a 1.22-meters border between each plot. The fertilizer 

 was applied in split applications with equal amounts applied on 1 May, 

 22 June and 26 July 1972. Samples were harvested 20 September 1972 by 

 clipping a 1-square meter sample from the short height zone of each plot 

 and a 0.25-square meter sample from the tall height zone of each plot. 

 The samples were dried in a forced-air oven at 70° Centigrade and weighed. 



The marsh at Oak Island differs from that at Ocracoke in several ways 

 which would cause the response to fertilizer applications to be different. 

 The most important difference is that the sediments which form the sub- 

 strate of the marshes are different. At Ocracoke the substrate is almost 

 pure sand, while at Oak Island it is much finer-textured (silt loam with 

 10 percent organic matter) and would be expected to be inherently more 

 fertile. Another difference is that the Oak Island marsh is older with 

 well-developed tidal creeks and distinct zonation of height forms. A 

 third difference is the greater tide range at Oak Island (1.3 meters) 

 which floods the marsh twice a day and is seldom affected appreciably by 

 the wind. 



The experimental fertilizer plots at Oak Island contained the tall 

 and short forms of S. alterniflora. Neither growth, chemical composition 

 of the plant tissue or general appearance of the tall form, was signifi- 

 cantly affected by additions of iron or nitrogen (Tab. 39). This is 

 probably because the creek bank area is adequately supplied with nutrients 

 from fresh sediments deposited by the overflowing creeks at floodtide. 

 Levees which- form are evidence of greater deposition along creek banks. 

 The meandering of creeks may expose fresh sediments which have not been 

 exploited by plant roots. If nutrients are taken up directly from the 

 tidal waters, then the tall height zone area is in a favorable position 

 for more frequent and longer inundation. However, it is also possible 

 that fertilizer applied to the sediments in the tall zone of S. alterni- 

 flora is dissolved in the estuarine water on floodtide rather than being 

 taken up by the plants. Fewer fine roots are near the sediment surface 

 in the tall S. alterniflora than in the short; consequently, uptake of 

 nutrients applied to the surface might be less. Calculation of the apparent 

 recovery of fertilizer-nitrogen for plants from the tall height zone which 

 received 336 kilograms per hectare of nitrogen indicates that only 3.2 

 percent of that applied was recovered in the grass shoots. 



Growth in the zone of short S. alterniflora was enhanced by the addi- 

 tion of nitrogen but was not affected by the iron treatments (Tab. 39). 

 The characteristic chlorotic appearance of short S. alterniflora was 

 unaffected by iron, but nitrogen produced a greener appearance. Plots 

 which received applications of nitrogen fertilizer yielded about twice as 



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