200 FUNDAMENTALS OF FRUIT PRODUCTION 



of plant nutrition. Much important information has been obtained 

 regarding changes occurring in the soil and something is known of the 

 synthesis, translocation, storage and utilization of organic materials. 

 At best, however, this information is fragmentary and much generah- 

 zation regarding the use of fertilizers in the orchard is unsafe. Some 

 idea of the complexity of the problem is obtained when we consider 

 the numerous ways in which fertilizers may act: (1) to change conditions 

 in the soil and (2) to disturb or restore equilibria within the plant. 

 Among the more important of these methods of action may be mentioned 

 the following: 



1. Altering the physical properties of the soil. 



2. Affecting the displacement (lyotropic succession) of various elements. 



3. Changing the solubility of other soil constituents. 



4. Changing the availability of other soil constituents. 



5. Changing the concentration of the soil solution. 



6. Changing the reaction of the soil solution. 



7. Influencing bacterial activity in the soil. 



8. Correcting or disturbing the balance between certain soil constituents, e.g., 

 calcium and magnesium antagonism. 



9. Stimulating or checking chemical reactions in the soil or absorption by the 

 roots. 



10. Acting as toxins or protecting against their influence. 



11. Serving directly as nutrients for the plant. 



12. Restoring or disturbing chemical equilibria within the plant after absorption. 



The Fertilizer Requirements of the Orchard. — In the discussion that 

 has preceded some attention has been devoted to each of these factors 

 in the nutrition of the plant. There has been presented also a general 

 resume of some of the available information regarding synthesis, trans- 

 location and use of certain plant constituents. Incidentally the following 

 facts have been brought out: 



1. Many elements that evidently are not required are found in plants. 

 Seldom are they harmful; they are merely tolerated. Among them may 

 be mentioned sihcon, aluminum, sodium, manganese, titanium and 

 probably chlorine. These elements are not required in fertilizers. They 

 may be combined with certain others that are of importance and they may 

 have some indirect influence upon the physical condition of the soil or the 

 chemical nature of the soil solution. They may often serve a useful pur- 

 pose in furnishing some of the so-called "indifferent" ash and occasionally 

 some distinctly beneficial response attributable to their presence may be 

 obtained when they are carried in fertihzers, but on the whole they need 

 not be given serious consideration in the problem of orchard fertihzation. 



2. Certain elements are found universally in plants and are necessary 

 constituents; however, except in very unusual cases, they exist in the soil 

 in sufficient quantities and in forms sufficiently available to meet the 

 requirements of orchard trees. The plant often takes up more than it 



