228 



P. L. Gersper et al. 



o 



X 



E 

 u 



O 



E 



C7> 



16 



12 







4 - Na 





V\ 



A 



(A 



Wet Moist 

 Meadow 



Basin Trough Rim Top 

 Polygon 



FIGURE 7-7. Average 

 quantities of exchange- 

 able cations and cation 

 exchange capacity in the 

 upper 10 cm of the soils 

 in 1972. 



ent microtopographic units. For example, average CEC within the upper 

 10 cm of soil in summer 1972 was approximately 50 meq (100 g)"' in wet 

 meadows and 69 meq (100 g)"' in mesic meadows. In polygonized terrain 

 the averages were 44, 70, 89 and 91 meq (100 g)"' in the troughs, rims, 

 basins and tops of high-centered polygons, respectively. 



Variations in CEC among the microtopographic units were different 

 when measured on the basis of volume rather than weight of soil, be- 

 cause of variations in bulk density. For example, soils of polygon 

 troughs had a CEC of approximately 27 meq (100 cm)"^ in the upper 10 

 cm compared to 25 meq (100 cm)"^ in the upper 10 cm of polygon basins 

 (Figure 7-7), even though the CEC on a weight basis in the soil of the 

 basins was more than double that of the troughs [89 versus 44 meq (100 

 g)"']. Thus, actual concentrations of nutrients in the soils of troughs were 



