solution has often been suggested as a cause for reduced growth of S. 

 alterniflora (Mooring, Cooper, and Seneca, 1971) . 



The reason for the appearance of calcium concentration in the plant 

 tissue at the fall sampling date (CCa) in the regression equation cannot 

 be readily explained. The means (Tab. 32) and the simple correlations 

 (Tab. 27) show no obvious relationships between yield and calcium con- 

 centrations in the plant. It probably enters the regression equation 

 because of its relationship to other variables. 



Manganese concentration in the plant tissue at the first sampling 

 date (AMn) and the second sampling date (BMn) and soil manganese (S-Mn) 

 are all negatively related to yield." The solubility of soil manganese is 

 increased under conditions of poor aeration. The importance of manganese 

 in the regression equation may be an indication that the more reduced 

 soils produce lower yields of S. alterniflora. The chemical environment 

 produced by waterlogging of soils produces several toxicity problems which 

 have been studied in relation to reduction of rice yields. Common problems 

 are iron, manganese and sulfide toxicity and toxicity from soluble organic 

 products (Black, 1968) . However, manganese toxicity is unlikely because 

 of the concentration in the plant tissue (Tab. 32). Concentrations of 

 10 times this amount were found with no apparent ill effects to plants in 

 growth chamber studies with S. alterniflora in which the nutrient source 

 was modified Hoagland's solution (Hoagland and Arnon, 1950). 



Phosphorus concentrations in the plant tissue at the first sampling 

 date (AP) and the second sampling date (BP) and soil phosphorus (S-P) are 

 positively related to yield. The need for adequate supplies of phosphorus 

 for plant growth is well known, and phosphorus is often a limiting factor 

 in the growth of plants. 



Sulfur at the first sampling date (AS) is negatively correlated with 

 yield. The means in Table 32 clearly show that concentration of sulfur 

 is much less in plants from the tall height zones. It is impossible to 

 determine from the data if this is a dilution effect or if more sulfur is 

 available in the short -height zone. 



e. Interpretation of the Height Model . Since some variables in this 

 model are also correlated, caution must be observed in interpreting regres- 

 sion coefficients. 



The sulfur concentration in the plant tissue at the second sampling 

 date (BS) accounts for the highest amount of variation in height in the 

 regression equation. Sulfur concentration at the first sampling date (AS) 

 also appears in the equation. The sulfur concentration at the second 

 sampling time is the single variable with the highest R 2 in both the 

 height and yield equations (Tab. 32). There is a clear relationship 

 between increased sulfur concentration and decreased growth, but it is 

 impossible to determine from the data if it is a cause and effect relation- 

 ship. 



119 



