KATIO OF CROP TO PHOSPHORIC ACID IN SOIL. 149 



From a chemical analysis made by Dr. Zoeller, of 

 the Munich Laboratory, the soil of this field was found 

 to give up to cold hydrochloric acid a quantity of phos- 

 phoric acid, which, calculated per hectare to a depth of 

 25 centimetres, amounted to 2376 kilogrammes = 5170 

 kilogrammes of phosphate of lime. 



The quantity of phosphoric acid in the corn and 

 straw of the crop reaped amounted together to : 



kilogr. Its. 



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 ^th 

 of the phosphoric acid supplied in the manure. 



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

 ditional 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 crop of corn and straw required 

 for its formation, 9 kilogrammes of phosphoric acid 

 would have sufficed to double the produce of the Tin- 

 manured plot ; but in the way in w r hich 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 p^art of phosporic acid, it was necessary to sup- 

 ply 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 3 ^ th 

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

 in the surplus crop is ^' 3 th of the phosphoric acid sup- 



