regular flooding of the marsh for a week or more causing an increase in 

 the salinity of the soil solution as evaporation proceeds. Measurements 

 of salinity of the soil solution were made only at harvest time each year. 

 The salinity was 36 parts per thousand on 2 September 1971 and 30 to 34 

 parts per thousand on 11 September 1972. Although no data are available, 

 it was suspected that there were periods of salt buildup earlier in the 

 1972 growing season. 



The standing crop of roots and rhizomes in the upper 30 centimeters 

 was increased significantly by nitrogen fertilization in 1972 (Tab. 36). 

 There was no response to nitrogen rates above 168 kilograms per hectare, 

 indicating that this rate of nitrogen was adequate for maximum growth of 

 roots and rhizomes. When root and rhizome weights are broken down from 

 to 10- and 10 to 30-centimeter layers, a variable response to fertili- 

 zation is noted. In the to 10-centimeter layer there was a significant 

 response to nitrogen and no response to phosphorus similar to the case 

 when the total weight of the upper 30 centimeters is considered. However, 

 in the 10- to 30-centimeter layer there was a significant response to 

 phosphorus but not to nitrogen. The overall means of 120 core samples 

 show that 75 percent of the roots and rhizomes are in the 0-to 10-centi- 

 meter layer and only 25 percent in the 10 to 30 -centimeter layer. From 

 field observations, almost all the roots and rhizomes were contained in 

 the upper 30 centimeters and any below this depth would be an insignifi- 

 cant part of the total weight. Results of separating roots and rhizomes 

 from 10 randomly selected core samples indicated that in the to 10-centi- 

 meter layer, the percentages by weight were 49.6 percent roots and 50.4 

 percent rhizomes. In the 10 to 30-centimeter layer, only 34.6 percent 

 of the dry weight was roots with rhizomes accounting for 65.4 percent. 

 Since there was a higher proportion of rhizomes in the 10 to 30-centimeter 

 layer, it is possible that the response to phosphorus in this layer is due 

 to an increase in rhizome growth -- that is, the response to phosphorus is 

 relatively greater for rhizomes than for roots. The increase in dry weight 

 of the to 10-centimeter layer was probably due to an increase of root 

 growth in response to nitrogen fertilization. 



The total dry weight of roots and rhizomes in the upper 30 centimeters 

 exceeds the dry weight of shoots (Fig. 61). Since the response of roots 

 and rhizomes to fertilization is less than the response of shoots, the 

 ratio of shoots to roots and rhizomes increases with nitrogen rate from 

 0.29 for the check to 0.75 at the highest rate of nitrogen. 



The same fertilization treatments were continued on the plots during 

 the 1973 growing season. The yield of aboveground growth (Tab. 37) was 

 increased significantly by nitrogen applications in combination with phos- 

 phorus; however, yields were not as great as in 1972. Other factors such 

 as rainfall and wind direction (which controls tidal flooding at this 

 location) cause year-to-year variations in shoot yields. 



Underground growth also showed a significant increase due to fertili- 

 zation, particularly to phosphorus (Tab. 38). 



132 



