272 PLANT PROPAGATION 



PHOSPHORIC ACID AND POTASH REMOVED FROM SOIL BY VARIOUS CROPS 



368. Effects of nursery crops on soil. Roberts of Cor- 

 nell University has published analyses of nursery stock 

 to show what plant food is removed by the four leading 

 kinds of fruit trees. The quantities appear in the follow- 

 ing table : 



POUNDS OF FERTILIZING COMPOUNDS NEEDED BY NURSERY STOCK 



The significance of these figures can best be appre- 

 ciated by a comparison with those of other crops; for 

 instance, silage corn. This crop grown in drills yields 

 12 to 20 tons an acre and will repeat the performance on 

 manured land, fully as well, at least once. Yet, to quote 

 Roberts's statement, "The amount of green corn necessary 

 to remove an equal amount of fertilizing ingredients 

 per acre, taking the average of the . . . nitrogen, 

 phosphoric acid, and potash . . . removed by an 

 acre of trees (three years' growth), would be 4,779 

 pounds." Nursery trees are, therefore, seen to take only 

 small amounts of plant food from the soil. Nursery 

 lands, it is reasoned, should supply three to ten times the 

 plant food needed by the trees. Experience also supports 



