7i8 



Circular No. 12 



The quantities of the same constituents used by some of the common 

 crops are shown in Table 2 ; they appear small in comparison with the 

 amounts given in the first table: 



TABLE 2. Composition of Crops 



Corn grain, 50 bushels. . 

 Corn stover, 1.5 tons. . . 

 Wheat grain, 25 bushels 

 Wheat straw, 1.75 tons. 



Clover hay, 2 tons 



Potatoes, 150 bu.'^hels. . . 

 Apples, 300 bushels . . . . 

 Apple leaves, 2 tons. . . . 



The elements in the soil are chemically combined in the mineral par- 

 ticles and in the organic matter, and only a small proportion is in the 

 soluble or available form at any one time. A chemical analysis can deter- 

 mine the total amount of any particular constituent present, but this or 

 any other laboratory determination cannot indicate what part of this 

 total is available to plants as the soil lies in the field. 



2. Very little relation between chemical analysis and fertilizer response. — 

 Experience covering many years and on a great variety of soils has shown 

 that a laboratory determination of the availability of a soil is not often 

 a reliable guide to the kind of fertilizer to which crops respond on that 

 soil in the field. The deficiencies of certain constituents such as nitrogen 

 and lime are frequently indicated by the physical characteristics of the 

 soil. The absolute deficiency of other constituents is rare and does not 

 warrant the College in making a chemical analysis to settle this point. 



3. Other factors. — Several other factors may have much more influence 

 on the productiveness of the soil than does the amount of plant food con- 

 tained. The moisttire supply may be poorly regulated; there may be 

 too much or too little at certain seasons. Lime may be needed to sweeten 

 the land, organic matter may be deficient, the tilth may be bad, all of 

 which factors determine the availability to the crop of the food in the 

 soil; and these should first be adjusted so far as possible. This is neces- 

 sary even when fertilizers are used. 



