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The Cornell Reading-Courses 



of an acre foot of soil is 3,500,000 pounds. Of nitrogen, the soil usually 

 contains several hundred, and often several thousand, pounds per acre. 

 All this material is normally in a form not readily available, and requires 

 manipulation in the form of drainage, tillage, etc., to release it for crop use. 

 The use of fertilizers, or the artificial addition of food to the soil, may 

 be, and often is, necessary for the best results. But many farmers make 



Fig. 10. — An example of good soil tilth. This physical condition is essential to the proper 



operation of any soil 



the mistake of assuming that this is the first and about the only condition 

 of growth, whereas bad physical condition of the soil, lack of humus, poor 

 drainage, or bad tillage, may be much more in need of consideration. 

 Fertilizers should come only after these other conditions have been at- 

 tended to. They are the means by which the store of food in the soil is 

 made available to the plant. 



It is not often possible to determine by any laboratory analysis the 

 kind of fertilizer to which the soil will respond. The only reliable 



