Improving the Chemical Nature of the Soil 85 



the needs of a particular field is to make trials, using 

 a variety of fertilizers, and thus observe what fertilizer 

 gives most satisfactory results. These tests must be 

 made for each soil formation. (See ^ 133.) 



118. Kinds of Fertilizers. Fertilizers are variously 

 classed, according to the valuable element they supply, 

 as "nitrogenous", "phosphate" or "potash" fertilizers. 

 Substances containing all three constituents are termed 

 "complete" fertilizers; or according to source, as home 

 fertilizers, or commercial fertilizers. In most instances 

 the substances applied to the land contain more than 

 one valuable element, as, for instance, composts, which, 

 being made out of plant remains, contain all the mineral 

 elements found in plants. 



119. Potassium Fertilizers. The most important 

 source of potash fertilizers is the famous Stassfurt mines 

 of Germany. The most common forms known to the 

 markets are the sulphate, muriate and kainit the latter 

 a mixture of several salts. All are readily soluble and 

 therefore are classed as "quick fertilizers." Wood-ashes 

 form an important source of potash, though their 

 value depends much on the source, and the way in 

 which they have been cared for. If leached out by the 

 rains, their value as a fertilizer is much lessened. Lime 

 and gypsum often have the effect of potash fertilizers, 

 causing the decomposition of insoluble potash com- 

 pounds in the soil, and thus indirectly acting as potash 

 fertilizers. The "home-made lye" obtained from ashes 

 is largely potash. 



120. Phosphorus Fertilizers. Phosphorus is an im- 

 portant fertilizer. Three-fourths of the phosphorus 

 absorbed from the soil is deposited in the grain of the 

 crop, and is, therefore, ordinarily sold from the farm, 



