60 ELEMENTARY AGRICULTXTRAL CHEMISTRY 



the percentage amount of each constituent present, is often of 

 little use in leading to any judgment as to its fertility or 

 manurial requirements. A case illustrating this point may be 

 quoted. T^70 pasture soils, A and B, gave the following 

 results on analysis : 



A. B. 



Per cent Per cent. 



Moisture . 3'13 1-70 



Loss on ignition 10'85 7'79 



(Nitrogen 0-274 0247) 



Insoluble matter 67-38 80-28 



Ferric oxide and alumina . . . 15*61 8-16 



Lime 0-29 0-13 



Magnesia 031 0-21 



Potash 0-86 0*48 



Phosphorus pentoxide .... 0-15 0*12 



Not determined 1-42 1-13 



100-00 100-00 



From these numbers A is evidently better provided with lime 

 and phosphorus pentoxide than B, and since there is also 

 more nitrogen present it would seem that B needed phosphoric 

 acid and lime more than A. Actual trial shows just the 

 opposite ; for basic slag (containing chiefly calcium phos|^hate 

 and free lime) gives a decided increase of crop on soil A, but 

 iias no marked effect on soil B. 



Evidently the phosphoric acid and lime in B, though less in 

 amount, are more available to the roots of plants than those in 

 soil A . Dr. Dyer suggested the determination of the amounts 

 of phosphoric acid and of potash which a soil could yield to a 

 solution of citric acid containing 1 per cent, of the acid, as a 

 means of estimating the amounts of these ingredients present 

 in an available form. This strength of acid was suggested 

 because it corresponds to the acidity of the sap contained in 

 the roots and root-hairs of many plants. By the application, 

 of this process to the two soils mentioned the following results 

 were obtained : 



A. B. 



Per cent. Per cent. 



" Available " potash 00062 00060 



« Available " pbosphorus pentoxide . 00049 00205 



