58 



Table I.— Relative Plant-Food Draft of Wheat and Apples. 



(In lbs. per acre annually, based on American and German Aver- 

 ages.) 



Wheat Wheat Wood Lvs. Fruit Apple 



Grain Total Lb. Lb. Lb. Total 



Annual weights, , 1,500 4,200 3,500 3,500 24,500 31,500 



Nitrogen (N), 30.0 43.7 11. 3 25.6 16.2 53.1 



Phos. acid (P2O5), . 10. o 15.8 3.6 5.3 6.4 15.3 



Potash (K2O), 9.8 26.8 6.6 15.9 41.5 64.0 



Lime (CaO), 0.84 8.0 29.1 29.5 3.0 61.6 



Magnesia (MgO), .. 3.0 6.1 4.4 8.9 3.4 16.7 



Iron (FeO), 0.5 1.5 0.8 2.8 



In the first place it will be noted, that in total food draft, the 

 apples exceed the 25-bushel wheat crop in every constituent except 

 phosphoric acid, and in it they fall behind only by half of a pound. 

 Notwithstanding this fact the trees are usually able to maintain 

 themselves much better and longer than wheat. This is probably 

 largely because of their much longer season of root-activity, their 

 more natural demands,* the annual return of most of the plant 

 food in their leaves, and their ability to curtail production for one 

 or more seasons when conditions become unfavorable. Without 

 going into details, however, it is quite evident that very important 

 amounts of plant food are annually removed by an apple orchard. 

 Scarcely any soil can furnish all these materials indefinitely in the 

 amounts and times required, and unless proper assistance is ren- 

 dered, there must come a time when production is materially re- 

 duced and off-seasons occur. 



It is also interesting to note the relatively large amounts of 

 nitrogen, potash, and lime, and the comparatively small amount of 

 iron annually taken up by the apples. Nearly all the lime remains 

 in the wood and leaves, while a large proportion of the potash is 

 found in the fruit. 



This large amount of lime seems to have some significance, so 

 far as the wood is concerned, because, as shown later, in most of 

 our experiments, its application has improved the growth. In view 

 of the small amount of lime required by the fruit, however, its 

 application should not be expected to materially affect the yields, and 

 this corresponds with our field results. Moreover the total effect 

 of adding lime alone surprisingly small, in comparison with the 

 relatively large amounts that are taken up. Either these amounts 

 are merely drawn in and deposited mechanically by the transpira- 

 tion stream, and hence are largely without physiological significance, 

 or else the average soil is still able to supply the lime needed. 



♦This is especially marked in the case of the fruit as compared with the 

 demands of the grain in wheat. For further discussion, see article by the 

 writer in the Annual Report of the Pennsylvania State College for 1910-11, 

 pages 447 to 449. 



