,48 Report of the Acting Director and Chemist op the 



jgaade here to define tliem in accordance with the best usage of the 

 terms. 



A Direct Fertilizer is one tJiat contains elements of plant-food^ 

 ■ which are availahle at once, that is, which can be taken up and used 

 immediately by plants. 



The term Available is applied to plant-food which is soluble, that 

 is, in such a condition that the roots of the plant can take it up 

 readily in solution. 



Plant-food is Unavailable, when it is in an insoluhle form, so 

 that the roots of the plant fail to take up any part of it. A large 

 proportion of plant-food present in the soil is unavailable, but by the 

 action of air, water, carbonic acid, etc., it is gradually changed to 

 soluble or available forms, which the plant can take up and use. As 

 will be noticed later, phosphoric acid in the form of insoliible cal- 

 cium phosphate or phosphate of lime is unavailable as plant-food, 

 but when converted into a superphosphate or soluble calcium phos- 

 phate, it becomes available. Unavailable plant-ft)od ys> potential 

 food or food in reserve. 



An Indirect Fertilizer is one which does not furnish to the soil 

 any needed plant-food and which may not he plant-food at all, hut 

 which is charoAiterized hy the way in which it acts on, the rnatter al- 

 ready in the soil, changing m,ore or less ofitfro')n iinavailcdile plant- 

 food to an availahle form. For example, lime, gypsum, salt, etc., 

 are indirect fertilizers, as they are generally used by farmers. 

 Later some attention will be given to the action of some of the 

 most familiar indirect fertilizers. They are commonly used by 

 farmers, not because the elements they furnish are lacking in the 

 soil, but because they can act upon unavailable plant-food and render 

 it available, or because they may have some beneficial influence 

 upon the mechanical condition of the soil. 



Natural Fertilizers include the solid and liquid excrement of 

 animals, all kinds of vegetable refuse, green crops for plowing 

 under, cotton-seed, mucks, marls, etc. 



Artificial Fertilizers are also known by such names as commercial 

 fertilizers, chemical fertilizers, etc., and are artificial preparations 

 or mixtures of fertilizing materials sold under trade names. The 

 fertilizing materials used in making these mixtures include the 

 substances found in natural deposits and by-products of numerous 

 industries, which are obtainable by farmers only through the 

 ■channels of trade. Some substances which might be classed as 



