1. The Crop Adaptation. While the chemical condition of a 

 soil is not altogether without influence in determining the crops to 

 which it is suited, this, as a rule, at least within such range of soil 

 variation as exists in this state, plays a much less important part 

 than mechanical and physical peculiarities. The crops to which a 

 soil is suited aie determined chiefly by its drainage, its capacity to 

 hold and to conduct water, its temperature and its aeration, and 

 these in turn are determined by the mechanical structure of the soil 

 and sub-soil. Variations in the proportions of gravel, sand, silt, and 

 clay, and not in chemical composition, cause the usual differences in 

 these respects. The varying proportions of these, therefore, usually 

 determine the crops to which a soil is suited. 



2. Fertilizer Requirements. The results of a chemical analysis 

 of a soil do not, as a rule, afford a satisfactory basis for determining 

 manurial requirements. The chemist, it is true, can determine what 

 the soil contains, but no ordinary analysis determines with exactness 

 what proportion of the several elements present is in available form for 

 the crop. Indeed, there is no such thing as a constant ratio of availa- 

 bility. While one crop finds in a given soil all the plant food it re- 

 quires, another may find a shortage of one or more elements. 

 Further, on the very same field one crop may find an insufficient 

 amount of potash, another may find enough potash for normal 

 growth, but insufficient phosphoric acid ; while a third may suffer 

 only from an insufficient supply of nitrogen. 



Most of our soils are of mixed rock origin, and, as a rule, possess 

 similar general chemical characteristics, providing they have been 

 farmed under usual conditions. The manurial and fertilizer require- 

 ments are determined more largely in most soils by the crop than by 

 peculiarities in the chemical condition of the soil. 



3. Crop Diseases. In some cases, the correspondent reports 

 that his crop is di-seased, and that he desires a chemical analysis in 

 order to ascertain what is the cause. The chemical composition of the 

 soil may in some instances exercise a controlling influence in deter- 

 mining a condition of health or disease, and is never unimportant 

 from the standpoint of vigorous, normal and healthy growth ; but in 

 the case of most diseases, the immediately active cause is the pres- 

 ence of a parasitic fungus, and this fungus is usually capable of 

 fixing itself upon the plant whatever may be the composition of the 

 soil. A knowledge of the chemical composition of soils, therefore, j 

 will not make it possible to advise such manurial or fertilizer treat-] 

 ment as will insure immunity from disease. 



