soil seriously. In other words, they will break up the large 

 aggregations of soil particles of considerable size into such an 

 increased nunjber of smaller ones, that the soil will bake worse 

 than before and become exceedingly difficult to till. 



I recall having seen an instance of this kind in connection 

 with experiments conducted by Professor Wohltmann at 

 Poppelsdorf near Bonn, Germany, in 1898. Land which had 

 been fertilized with nitrate of soda year after, year finally 

 became so compact and baked so hard that it was almost 

 impossible to work it. If nitrate of soda is used on a sandy 

 or gravelly soil which does not contain much clay or silt, this 

 danger is, of course, not to be feared. 



In semiarid regions where alkaline soils prevail the results 

 from using nitrate of soda year after year as the sole source of 

 nitrogen ma}' prove detrimental, not only because the soil is 

 deflocculated, but also because it is rendered too alkaline for 

 the best growth of many plants. 



It must be borne in mind in connection with the use of 

 nitrate of soda that it moves freely up and down in the soil. 

 If, therefore, nitrate of soda is used in considerable quantities 

 on open sandy and gravelly loams, such as abound in many 

 parts of New England and particularly in eastern Massachu- 

 setts, there is danger that heavy rains may wash considerable 

 of it out through the subsoil. On soils of a heavy clay or silt 

 type, however, the danger of loss by leaching would not be so 

 great. 



Sulfate of ammonia has certain distinct advantages over 

 nitrate of soda as a source of nitrogen, for the reason that the 

 ammonia enters into chemical combination with the silicates of 

 the soil in the same manner as lime, magnesia, soda, and 

 potash are known to do. When the ammonia is thus com- 

 bined, it is not readily subject to loss by leaching. Neverthe- 

 less, it gradually becomes available and is taken up by the 

 crops either as ammonia or as nitric acid after its nitrification. 

 In the meantime, it is held in a safe combination in the soil. 



In one particular, sulfate of ammonia acts differently from 

 nitrate of soda. For example, if sulfate of ammonia is used 

 year after year on land which is slightly acid or considerably 

 acid at the outset, the acidity gradually increases. This is 



