Table 6. Critical concentrations and the range of 

 concentrations of essential nutrient 

 elements in index segments of Elodea occidentalis , 



Index Critical Range in 



Element segment cone. cone. 



N 2nd 1" 1.60% 1.14- 4.32% 



P 2nd 1" 0.14% 0.06-0.35% 



S 2nd 1" 0.08% 0.06-0.46% 



Ca 1st 1" 0.28% 0.17-0.62% 



Mg 2nd 1" 0.10% 0.06-0.19% 



K 2nd 1" 0.80% 0.25-2.51% 



Fe 1st 1" 60 ppm 40-219 ppm 



Mn 1st 1" 4.0 ppm 2.2 -16.7 ppm 



Zn 2nd 1" 8.0 ppm 3.6 -34.4 ppm 



Mo 1st 1" 0.15 ppm 0.04-6.4 ppm 



B 1st 1" 1.3 ppm 0.3 -11.2 ppm 



Critical Concentrations in Ceratophyllum 



Although Elodea occidentalis was selected as the primary 

 organism on which to base the plant analysis assay, the 

 critical concentrations of nitrogen, phosphorus, and 

 several other elements were established in Ceratophyllum 

 demur sum . These are presented in Table 7. 



The critical nitrogen concentration in the second one-inch 

 segment of Ceratophyllum was 1.30 percent. This value 

 is in agreement with the critical concentration reported 

 for entire Ceratophyllum demursum plants in a previous 



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