SOIL FERTILITY 



147 



sorption capacities, different exchangeable calcium levels and different 

 percentage calcium saturations of the exchange complex. It was found 

 that at any given level of exchangeable calcium, the quality of fruit was 

 lower when produced in bentonite or muck. At any given cation-ad- 

 sorption capacity the percentage of well-filled pods increased with an in- 

 creasing degree of calcium saturation. Yet, when the percentage calcium 

 saturations were of the same order the higher calcium levels produced 

 the better quality of fruit. These workers pointed out that both the per- 



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bJ 



O 90 



q: 

 uj 80 



CL 



I 



O 



txJ 



in 



70 

 60 

 50 



z 20 



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% 10 



B 



02 OA Oj6 08 1.0 1.2 1.4 1.6 1.8 2.0 22 2A 

 M.E. Ca per 100 GM. — COLLOID -SAND MIXTURE 



Figure 7. — Percentage ovarian cavities of peanuts filled as afifected by type 

 of colloid, cation-adsorption capacity and calcium level. Mehlich and 

 Col well (72)_. 



centage calcium saturation and calcium level would have to be considered 

 in determining the need for calcium in peanut soils. 



A comparison of the relative availability of calcium in soils of dif- 

 ferent types of colloids is shown in figure 8. Using the percentage of filled 

 nuts as a criterion of calcium availability, it is evident that a small amount 

 of calcium is much less effective in a soil high in organic colloids than in a 

 soil in which the cation-adsorption capacity arises from kaolonitic-type 

 minerals. Furthermore, it is evident that greater amounts of calcium 



