' SOIL FERTILITY 155 



differences in lime response which have been observed with strains of 

 the same variety (table 7). 



Some of the experimental evidence might suggest that the differences 

 in response of varieties or types of peanuts to fertilization are, to a cer- 

 tain extent, a function of seed size. Such may be the case, or the unequal 

 response to fertilization may be due to other genetic differences not as- 

 sociated with kernel size. At any rate, it is fallacious to attempt to classify 

 all peanut varieties in two categories, a large-seeded group and a small- 

 seeded group, because of the gradation in kernel size, with no sharp differ- 

 entiation which would permit such broad groupings. Certainly the dif- 

 ferences in seed size and behavior of peanut varieties within either of 

 the so-called major-size groups would limit generalizations as to their re- 

 sponsiveness to fertilization. 



Considering the differences in varietal response to fertilization, it 

 is very evident that research programs in peanut breeding and soil fer- 

 tility should be inseparable. In comparative tests of several varieties, it 

 has been demonstrated that an apparently superior variety may be defi- 

 nitely inferior under different environmental conditions. Therefore, in 

 evaluating peanut varieties, it is essential that they be grown at different 

 levels of soil fertility and under other variations in environmental con- 

 ditions. The fact that many of the present peanut varieties appear to be 

 relatively unresponsive to fertilization does not preclude the possibility 

 that varieties may eventually be developed which would respond to 

 fertilizer amendments much in the same manner as do many other crops. 



ROTATION AND MANAGEMENT PRACTICES AND THE 

 MAINTENANCE OF SOIL FERTILITY 



Several factors combine to make the problem of maintaining the fer- 

 tility of peanut soils especially acute. First, the native fertility of the soils 

 used for growing peanuts is relatively low. Furthermore, peanuts remove 

 relatively large amounts of certain nutrients from the soil with the normal 

 systems of management in which both hay and nuts are harvested. Since 

 peanuts have not been found to be as responsive to direct applications of 

 fertilizer materials as are many other crops, there is a tendency to supply 

 much less of certain nutrients than is removed from the soil by the crop. 

 Considering these factors, the problem is resolved to one of determining the 

 most effective and economical manner of obtaining high yields of peanuts 

 and other crops grown in rotation with them and, at the same time, main- 

 taining the fertility of the soil. 



