COMMERCIAL FERTILIZERS 73 



of much economic importance to farmers, and one which has received 

 much time and attention on the part of investigators in the agricultural 

 experiment stations of all the older agricultural states. Agricultural 

 literature now contains a vast amount of data setting forth the results of 

 experiments with fertilizers on different types of soil and for different 

 crops, hut there is still much to be learned relative to the subject. We 

 will always have an acute fertilizer problem. This is due to the constantly 

 changing conditions of the soil, resulting primarily from changed agri- 

 cultural practices and especially from the treatment of the soil, which 

 will gradually change its relationship to crops. 



What are Commercial Fertilizers? — In discussing the subject of 

 fertilizers the terms manures, complete and incomplete manures, fertil- 

 izers, chemical fertilizers, commercial fertilizers, natural fertilizers, arti- 

 ficial fertilizers, indirect fertilizers, superphosphates, etc., are used, and 

 there is often misunderstanding of the meaning of some of these terms. 

 Fertilizers are first divided into natural and artificial. The former in- 

 clude all the solid and liquid excrement of animals and green manuring crops 

 when plowed under for the benefit of the soil. Artificial fertilizers include 

 all commercial forms of fertilizers. These are sometimes called prepared 

 fertilizers and chemical fertilizers, but are becoming more generally known 

 as commercial fertilizers. A complete fertilizer contains the three essential 

 plant-food constituents, nitrogen, phosphorus and potassium. An in- 

 complete fertilizer contains only one or two of these. All animal manures 

 are complete fertilizers. Green manures are likewise complete. 



A fertilizer is said to be indirect when it contains none of the essential 

 plant-food elements, but in some way acts on the soil so as to increase the 

 availability of plant food in the soil or increase crop growth. Lime, 

 gypsum, salt and numerous other substances have been found to have 

 this action and would be classed as indirect fertilizers. 



The terms high-grade and low-grade are also applied to fertilizers. 

 These terms, however, are not well defined. High-grade fertilizers gen- 

 erally contain large amounts of plant food per ton, while low-grade fer- 

 tilizers contain relatively small amounts. Another distinction that is 

 sometimes made is that fertilizers manufactured out of high-grade con- 

 stituents, such as nitrate of soda, acid phosphate and muriate or sulphate 

 of potash, are considered high-grade fertilizers regardless of the percentage 

 of the elements. A high-grade fertilizer always costs more per ton than 

 a low-grade one, but it is generally true that the elements in such a fertil- 

 izer come cheaper to the farmer than they do in a low-grade material. 

 Whether it is more economical to purchase high-grade or low-grade material 

 is an important question, but the answer is not difficult. All fertilizers 

 should be bought on the basis of their content of available plant food, and 

 it is merely a problem in arithmetic to calculate the relative cost of the 

 elements in different grades of fertilizer. 



Where are Fertilizers Secured? — Fertilizer materials are to a large 



