SOILS AND FERTILIZERS 397 



A considerable number of manufacturing wastes, rich in nitro- 

 gen, but differing greatly in their value as plant foods, are now on 

 the market, and their use is urged uppn manufacturers of mixed fer- 

 tilizers. In general, such of these waste products as are agricultur- 

 ally of least value are also least expensive, and therefore the tempta- 

 tion to use them in manufactured goods is to some very strong. 



It is highly desirable to know in the first place how these nitrog- 

 enous wastes compare with each other, and with some standard, 

 such as nitrate of soda, in availability, and various experiments have 

 already accomplished something in this direction. In the next place 

 it is important, either to be able to identify these various "ammo- 

 niates" in mixed fertilizers, or else to have some means of dis- 

 tinguishing in such fertilizers between available and inert nitrogen 

 some measure of its availability. Unfortunately, it has hitherto 

 been difficult or impossible to identify with certainty most of the in- 

 ferior ammoniates either by inspection or by ordinary chemical 

 tests. The treatment with acid during the process of manufacture, 

 the grinding and the mixture with phosphatic material and potash 

 salts, so alters the structure and appearance that in many cases the 

 microscope fails to identify any thing and chemical tests are not 

 generally applicable. 



The most satisfactory, and, indeed, usually the only method 

 by which we can at present determine the needs of a soil is to ask the 

 question of the soil itself by growing a crop upon it with different 

 kinds of fertilizers and noting the result. Such soil tests with fer- 

 tilizers have in many cases given results of much immediate prac- 

 tical value for the locality in which they were undertaken. Many 

 materials containing the essential elements are practically worth- 

 less as sources of plant food because the form is not right. All ma- 

 terials containing organic nitrogen are valuable in proportion to their 

 rapidity of decay or change. Thus organic nitrogen differs in avail- 

 ability not only according to the kind of material which supplies it, 

 but upon the treatment it receives. The phosphoric acid in natural 

 or untreated phosphates is insoluble in water and not readily avail- 

 able to plants ; that is, the rate of availability depends largely upon 

 the rapidity with which the substance rots or decays, and the rate of 

 decay again depends upon the character of the substance with which 

 the phosphate is associated. Potash may exist in a number of 

 forms, though chiefly as chlorids, or muriates, in which case the 

 potash is combined with chlorin ; and as sulphates in which the pot- 

 ash is combined with sulphuric acid. With potash, however, the 

 form does not exert so great an influence upon availability as is 

 the case with nitrogen and phosphoric acid. All forms are freely 

 soluble in water, and are believed to be nearly if not quite equally 

 available as food. The form of potash has, however, an important 

 influence upon the quality of certain crops, due rather to the con- 

 stituents with which the potash is associated than to the potash itself. 

 The character or form of the materials used must, therefore, be care- 

 fully considered in the use of manure. All manufactured products 

 or brands of fertilizers are made up of a mixture of the various kinds 



