142 THE PEANUT— THE UNPREDICTABLE LEGUME 



that with certain plants calcium is not absorbed as readily in acid media 

 as in those of a higher pH. 



Peanuts are especially heavy "feeders" of potassium and the plant may 

 absorb considerably more of this element than is needed. Certainly it 

 would be desirable to reduce this luxury consumption of potash if the 

 yields were not adversely affected. There is considerable evidence (86, 

 87, 93, 113) that the addition of lime to soils will result in a decreased 

 absorption of potash by the plant. On the other hand, gypsum may in- 

 crease the uptake of K (93, 113). The differential effect of the two ma- 

 terials upon potash absorption provides another point in favor of the use 

 of limestone rather than gypsum for peanuts. 



On soils aSjsfextremely low-exchange capacity, it may be necessary to 

 ■'apply a soluble source of calcium in addition to lime in order to supply 

 adequate amounts of calcium. 



Recent fundamental studies (37, 46) have emphasized the specific 

 need of the peanut for calcium and have shown that cations of a similar 

 nature, such as magnesium, cannot be effectively substituted for calcium. 

 If the primary objective in using lime for peanuts is to supply the nutrient 

 calcium, it should be desirable to use a material which would be most ef- 

 fective in meeting that need. When the soil pH is increased beyond a cer- 

 tain point by liming, certain minor-element deficiencies may be en- 

 countered. Thus there is an obvious- limit to the amount of lime which 

 may be safely used. Yet dolomitic Hmestone is used almost exclusively in 

 some peanut-producing regions, and less than one-half the amount of cal- 

 cium is supplied by this material in liming a soil to a given pH as would 

 be added were calcitic limestone used. Therefore, from the standpoint of 

 meeting the calcium requirements of peanuts, it should be more desirable 

 to use a form of calcitic limestone rather than one high in magnesium. 



Some soils used for the production of peanuts are low in magnesium, 

 and the superiority of dolomitic limestone observed in certain experi- 

 ments has undoubtedly been due to a magnesium response. However, the 

 magnesium requirement of peanuts is relatively low and, on soils deficient 

 in this element, it might be desirable to supply the needed magnesium in 

 the fertilizer or to use a mixture of calcitic and dolomitic limestone. If 

 such a mixture were used, it would appear to be desirable to keep the 

 ratio of Ca to Mg in the liming material relatively high. 



Placement of Calcium 



Recent studies (40) have shown that much of the calcium absorbed 

 by the peanut roots is immobilized in the leaves and stems, and insuf- 



