NUTRIENT REQUIREMENT OF THE POTATO PLANT 



EARL S. JOHNSTON 



Maryland Agricultural Experiment Station, College Park, Maryland 



The importance attached by investigators to the nutrient 

 requirements of plants is shown by the increased amount of work 

 being done with sand and water cultures. Little if any work of 

 this nature has been done with the potato plant. The behavior 

 and growing habits of the potato make it less susceptible of this 

 kind of study than such plants as wheat and rice. Special 

 methods must therefore be devised before anything like compar- 

 able results can be obtained for this plant. Because of the eco- 

 nomic importance of the potato, preliminary experiments have 

 been started for the purpose of ascertaining methods of attacking 

 the problem of its nutrient requirement. 



In problems of this nature it is essential to obtain uniform 

 plants at the beginning of the experiment. Differences in growth 

 may then be attributed to differences in treatment. Individual 

 hereditary characteristics of course are always present, but of 

 necessity must be neglected. It is assumed that if plants or 

 seedlings are exactly alike as to their external appearances, their 

 internal characteristics will differ less than those that are unlike 

 externally. In water and sand culture work with wheat, uni- 

 form seedlings, sprouted from a pure strain of seed can be se- 

 lected with comparative ease. With the potato the problem of 

 selecting uniform plants is exceedingly difficult. This problem is 

 further complicated by the presence of the tuber on which the 

 plant grows. 



An attempt was made to secure uniform potato plants by 

 growing cuttings from the stems of old vines. This method 

 proved unsatisfactory as most of the cuttings produced small 

 tubers rather than roots and leaves. Figure 1 illustrates cut- 

 tings from Irish Cobbler stems. The tendency toward tuber 



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THE PLANT WORLD, VOL. 22, NO. 11 



