rates of and 74 kilograms per hectare of phosphorus. Nitrogen rates 

 were 0, 168, 336, and 672 kilograms per hectare of nitrogen supplied by 

 ammonium sulfate. An ammonium form of nitrogen was thought to be more 

 suitable to the marsh environment since it is the form of inorganic nitro- 

 gen found in greatest quantities in reduced soils. Application of nitrate- 

 nitrogen to poorly drained soils is undesirable since it is subject to 

 denitrification and loss to the atmosphere in gaseous forms (Keeney, 1973) . 

 The ammonium form has the advantage of being adsorbed by the exchange 

 complex of the soil. It is also possible (considering the flooded condi- 

 tion in which it grows) that S. aitern-iflora is adapted to utilization of 

 the ammonium form of nitrogen as has been reported for some other plants 

 (Townsend, 1966; Van Den Driessche, 1971) . 



The fertilizer materials were applied in split applications with equal 

 amounts on 12 May, 22 June, and 27 July 1971 by broadcasting evenly over 

 the substrate surface. Samples were harvested 1 September 1971 by cutting 

 a 0.61- by 1.52-meter swath from each plot with a Jari sicklebar mower. 

 Salioomia spp., dead stems of S. altermiftora from the previous year's 

 growth and other foreign matter, were separated from S. dltevnvflova 

 plants. The plants were dried at 70° Centigrade and weighed, subsamples 

 were ground in a Wiley mill, and analyzed for nutrient content by the 

 Department of Soil Science, Analytical Service Laboratory of North Carolina 

 State University. 



The experiment was continued in 1972 with the same rates of nitrogen 

 and phosphorus fertilizers applied in split applications on 13 April, 

 20 June, and 19 July 1972. The plots were clipped and raked in early 

 spring in 1972 to facilitate harvesting and ensure that all plant material 

 harvested in the fall was produced - in that growing season. Samples were 

 harvested 11 September by clipping a 0.61- by 3.96-meter swath from each 

 plot. The plant samples were dried and processed in the manner previously 

 described. Roots and rhizomes were also sampled in 1972 by taking five 

 cores 8.5 centimeters in diameter and 30 centimeters deep from each plot. 

 In the laboratory the cores were divided into to 10- and 10 to 30-centi- 

 meter layers and washed with tap water to remove the soil material. Ten 

 core samples were selected at random and roots were separated from rhizomes 

 to determine the relative proportions of each. The root and rhizome 

 samples were dried at 70° Centigrade. Combined root and rhizome samples 

 were processed and analyzed in the same manner as the shoots. 



The experiment was continued in 1973 in the same manner as in 1972, 

 except roots and rhizomes were not separated. 



The results of the nitrogen-phosphorus factorial experiment at Ocracoke 

 indicate that, although additions of nitrogen alone can increase yields 

 significantly, the availability of phosphorus quickly becomes limiting when 

 nitrogen rates are increased (Fig. 56) . Yields at the end of the first 

 growing season were increased only slightly by the addition of nitrogen 

 without phosphorus. The only statistically significant (0.05 level) 

 difference was between the yield of the check plots and those receiving 

 672 kilograms per hectare of nitrogen. However, when phosphorus was 



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