TlIK FKRTILITV OF TIIK SOU. 1 5 



remove 29.7 poiuuls of nitrogen, y.5 puuiuls of i)hi)>i)lu)ric acid 

 and 13.7 pounds of potash. Now if all the potential nitrogen, 

 phosphoric acid and potash could be rendered available, there 

 is present in such an average soil, in the tirst eight inches, 

 enough nitrogen to last 90 years, enough phosphoric acid for 

 500 years and enough potash for 1,000 years. 



Let us find out the amounts of nitrogen, phosphoric acid, 

 potash and lime removed per acre by some of our leading farm 

 crops. 



From these figures it is evident that all of the above soils 

 have sutiticient amounts of plant food to last for many years. 

 Corn yielding 65 bushels per acre, only takes away 85 pounds 

 of nitrogen, 32 pounds of phosphoric acid and 95 pounds of 

 potash. Mangels which are heavy users of potash only show a 

 removal of 150 pounds for a ten ton crop. When we compare 

 the amounts of these constituents removed by crops and the 

 total supply in the average soil we may better realize the amount 

 of stored up plant food in soils.* 



Plant Food not Available. — The question naturally arises, what 

 is the use of adding fertilizers or manure to soils when such 

 large amounts of plant food are present? The plant food in 

 the soil is dormant ; it is locked up ; it is unavailable. Available 

 plant food may be present but the condition of the soil may 

 be such that the plant cannot utilize it. The soil may be acid or 

 sour, or it may contain olijcctionable substances distasteful to 

 plants. 



The plant obtains its nourishment from the salts in solution 

 in the soil water and these soluble salts constitute the available 

 plant food. The chemist can determine the total plant food, or 

 the potential fertility, in the soil, but he cannot tell us how 

 rriuch is available. The available plant food supply may l)c 

 ascertained, to a certain extent, by carrying on field experiments. 

 The results of such experiments will of course vary with differ- 

 ent soils and different crops. The chemist can determine whether 

 a soil is acid, alkaline or neutral and from such data advise 

 whether lime would benefit the soil, the amoimt to apply and the 

 kind of fertilizers to use. In such cases a chemical aualvsis is 



