91 



In the matter of management, too, a considerable variation may be 

 observed. One soil may lose a large portion of its essential constituents, 

 because no pains are taken to retain for the use of the crop the consti- 

 tuents annually rendered available through the natural agencies of sun, 

 air, and water ; while in another, by means of careful cultivation and 

 the use of absorbents and catch crops, the constituents made available 

 are largely retained.' 



Crops differ in respect to their power of acquiring food. — The legumes, 

 a class of plants which includes the various clovers, paas, beans, 

 vetches, etc., differ from other plants in being able, under proper con- 

 ditions, to acquire their nitrogen from the air, and can therefore make 

 perfect growth without depending upon soil nitrogen. On the other 

 hand, the various grasses and grains are not only dependent upon soil 

 nitrogen, but they must have an abundance during their most rapid 

 period of growth in order to attain their maximum development. For 

 the latter class of plants favourable results are secured from the proper 

 use of nitrogenous manures, while for the former class the application 

 of nitrogenous manures simply results in supplying an element which 

 could have been secured quite as well by the plant itself, without 

 expense. Illustrations could be multiplied, though perhaps less strik- 

 ing than this, showing that the variations in crops in respect to their 

 power of acquiring food are really very great, and a right knowledge 

 of this fact has a most important bearing upon the economical use of 

 commercial manures. 



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

 Armsby, " 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 

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

 tical value for the locality in which they were undertaken. As a rule, 

 however, farmers have looked upon such experiments as something too 

 costly and complicated for them to undertake, and consequently they 

 have perforce been content to use fertilizers in a more or less hap- 

 hazard manner, and in many cases, no doubt at a great financial dis- 

 advantage." 



While such tests are not so difficult or expensive as is often sup- 

 posed it is recommended that before the farmer undertakes them for 

 the first time he seek the advice of some one familiar with the details of 

 such work. 



FORMS, SOURCES, AND COMPOSITION OF FERTILIZING MATERIALS. 



The term " form" as applied to a fertilizing constituent has reference 

 to its combination or association with other constituents, which may be 

 useful, though not necessarily so. The form of the constituent, too, has 

 an important bearing upon its availability, and hence upon its useful- 

 ness as plant food. Many materials containing the essential elements 

 are practically worthless as sources of plant food because the form is not 

 right ; the plants are unable to extract them from their combinations ; 

 they are " unavailable." In many of these materials the forms are 

 changed by proper treatment, in which case they become valuable not 

 because the element itself is changed, but because it then exists in such 

 form as readily to feed the plant. 



