32 THE AMERICAN FARMER. 



nourishment from it ; hence, the plant would just as surely starve for the want of that phos 

 phoric acid as though the soil contained none. In other words, the analysis determined the 

 constituents of the soil, but not its mechanical condition, upon which so much depends in 

 successful agriculture. Besides these objections, different samples of soil taken from 

 different portions of the same field might vary greatly in their composition ; hence, an 

 analysis of soil from one portion of a field might not apply to other portions. 



. Elements Necessary to Supply Soils. With respect to the obstacles met with 

 in chemical analysis, and the elements abstracted from the soil by different crops, Prof. W. 

 O. Atwater says: 



&quot; It was once thought that the chemical analysis of a soil would easily reveal its deficiencies 

 in plant food. But later experience has shown that this is, at best, a costly and very defective 

 source of information. Different samples of soil taken from different places in the same 

 field and at different times may vary widely in composition, and, what is a still greater diffi 

 culty, the chemical tests which prove the presence of a given ingredient in the soil, do not 

 tell whether it is already in such a form that the plant can use it, nor whether or how soon 

 it may become so. And there are many other factors of vital importance to the development 

 of the plant which soil analysis does not reveal. 



To find what materials crops remove from the soil is an easier matter. Thousands of 

 analyses of the more important vegetable products have been made, nearly all in Europe, 

 however, and we have tables prepared from them giving the average composition of our field 

 crops. From these any farmer may calculate how much plant-food a given crop takes on the 

 average from his soil. These figures might possibly fit his case no closer than would the cal 

 culation of his own weight from that of the average European, but they will suffice well 

 enough for practical purposes. 



Formulas for fertilizers for special crops are commonly based upon calculations of this 

 sort. For instance, a crop of fifty bushels of corn, with the stalks, would take from the soil 

 on the average, 



Nitrogen, 76 Ibs. Magnesia, 23 Ibs. 



Phosphoric acid, - - 51 &quot; Lime, - 27 &quot; 



Potash, - 72 &quot; Sulphuric md, 8 &quot; 



Now we may assume that nitrogen, phosphoric acid, and potash are the only ones the 

 soil will fail to furnish in plenty, or that if lime and sulphuric acid are needed in addition, 

 there will be enough in the superphosphates and other materials to be used to supply them. 

 &quot;We have then to provide 76 Ibs. of nitrogen, 51 Ibs. of phosphoric acid, and 72 Ibs. of 

 potash, in forms readily available for plant-food.&quot; 



The organic elements that enter into the composition of plants are four in number 

 oxygen, hydrogen, carbon, and nitrogen. All of these, with the exception of nitrogen, are 

 supplied by nature in sufficient quantities; though this is furnished to a certain extent, still 

 it is often found in such small quantities as to require an additional supply applied in order 

 to render its fertility available in the production of good crops. 



This mysterious element, nitrogen, in order to be beneficial to plants, must undergo a 

 chemical change. By uniting with oxygen, it forms nitric acid; by uniting with hydrogen^ 

 it forms ammonia, which is the form in which nearly all the nitrogen used by plants is taken ; 

 hence nitrogen and ammonia are often used, in connection with agriculture, as synonymous 

 terms. Both nitric acid and ammonia are powerful fertilizers. It is estimated by good 

 authority that the nitrogen in organic matter is worth only about three-fifths as much as pure 

 ammonia. Nitrogen in the form of ammonia, also in the form of nitric acid, is washed 

 down to the soil by water. The nitrates are carried in the water to the roots of plants; the 

 leaves also absorb nitrogen from the air, and in this manner the plants obtain their nitrogen. 



