148 ACTION OF SOIL ON FOOD OF PLANTS IN MANUKE. 



The quantity of phosphoric acid in the corn and straw 

 of the crop reaped amounted altogether to : — 



kilogr. lbs. 



From the manured plot . , 17-5 = 38-5 of phosphoric acid 

 From the unmanured plot . 8-0 = 17- 6 „ 



Surplus obtained by manuring . 9-5 =20* 9 „ 



In the 657 "4 kilogrammes of phosphorite the field 

 received altogether 241*4 kilogrammes of phosphoric 

 acid ; accordingly, the surplus amounted only to gV^^^ *^f 

 the phosphoric acid supplied in the manure. 



There is nothing surprising in this result, as the addi- 

 tional phosphoric acid was not given to the plants but to 

 the whole field. Had it been possible to surround each 

 root with so much phosphoric acid or phosphate of lime 

 as the surplus ccop of corn and straw required for its 

 formation, 9^ kilogrammes of phosphoric acid would have 

 sufficed to double the produce of the unmanured plot ; 

 but in the way in which the manure was actually applied, 

 every part of the field received an equal share of 

 phosphoric acid. 



Thus, of the total amount of 241-4 kilogrammes, only 

 9 '5 kilogrammes came into contact with the roots of the 

 plants, the remainder, though quite suitable for food, 

 remaining inactive. To enable the plant to take up one 

 part of phosphoric acid, it was necessary to supply the 

 field "with five-and-twenty times this quantity. 



On the other hand, the effect of the manure appears out 

 of all proportion greater as compared with the store of 

 phosphoric acid in the field. 



The quantity of phosphoric acid contained in the corn 

 and straw reaped from the unmanured plot is ^^^th of 

 the total amount of phosphoric acid in the field ; that in 

 the surplus crop is -^jt\^ of the phosphoric acid supphed 

 by the manure. As the manured plot gave double the 



