146 THE PEANUT— THE UNPREDICTABLE LEGUME 



0.7 m.e. of calcium per 100 grams. However, lime response was observed 

 on North Carolina soils with calcium levels up to approximately 1.4 m.e. 

 Two factors may have contributed largely to these differences: First, 

 small-seeded varieties of peanuts were grown in Alabama while the large- 

 seeded types were used in the work in North Carolina. It has been sug- 

 gested that large-seeded peanuts have a greater need for calcium than 

 the small-seeded type. Second, the peanut soils in Alabama are generally 

 of a lower exchange capacity than those used in North Carolina. The 

 availability of a given amount of exchangeable calcium might be ex- 

 pected to increase with a decrease in the base exchange capacity of the 

 soil. 



Rogers (95) pointed out that lime response was more closely corre- 

 lated with the exchangeable calcium level than with percentage calcium 

 saturation or with calcium soluble in one-tenth normal hydrochloric acid. 

 Colwell and Brady also found a better correlation between response to 

 calcium additions and exchangeable calcium levels than with percentage 

 calcium saturation of the soil. 



Recent investigations at the North Carolina Experiment Station (17, 

 18, 72, 73) have revealed some very interesting relations between soil 

 properties and the response of peanuts to calcium. Mehlich and Colwell 

 (72) studied the absorption of calcium by peanuts as affected by the type 

 of soil colloid using different levels of exchangeable calcium. These 

 workers used relatively pure colloidal materials of the 1 :1 and 2 :1 lattice 

 types and varied the adsorption capacity by diluting the materials with 

 quartz sand. With equal concentrations of calcium in sand-clay systems 

 more calcium was absorbed from the kaolonite or 1 :1 type mineral than 

 from the 2 : 1 type bentonite. The effect of type of clay on calcium avail- 

 ability was also evidenced by the quality of the fruit produced (figure 

 7) . A high percentage of filled pods was produced on kaolonitic colloids 

 even at relatively low calcium levels. In the bentonite systems larger 

 amounts of calcium were required to produce fruit of similar quality. 

 These workers observed that the uptake of calcium from kaolonite 

 systems was more directly related to the total calcium present than to the 

 degree of saturation. In the systems of 2 :1 type mineral the absorption of 

 calcium was found to be more directly related to the percentage calcium 

 saturation than to the total amount present. 



In a later investigation Mehlich and Reed (73) studied the behavior 

 of peanuts grown in systems in which the cation-adsorption capacity was 

 due to both organic and mineral colloids. Kaolonite, bentonite and muck 

 were used to prepare colloid-sand systems with different cation-ad- 



