COMMERCIAI. FERTILIZERS 63 



conditions, (4) the importance of early maturity, (5) the 

 possibility of irrigation, (6) the amount of land available 

 and (7) the character of the crop to be grown. Applica- 

 tions vary from a few hundred pounds to two or more 

 tons to the acre. One ton to the acre for a single crop is 

 considered liberal, although this amount is often ex- 

 ceeded. At Norfolk, Virginia, 3000 pounds are fre- 

 quently applied during the season. While dangers at- 

 tend the free use of fertilizers (109), the only sound 

 business policy is to apply the various elements in fully 

 sufficient quantities. Regarding this matter, Dr. Edward 

 B. Voorhees says (Voorhees, Fertilizers, p. 264) : "Apply 

 a reasonable excess of all the essential fertilizer constitu- 

 ents to all of the crops. Nevertheless, because of the 

 peculiarities of growth of the different plants, as well as 

 the different objects of their growth, distinctions should 

 be made in reference to the kinds and amounts of plant 

 food applied, and these conditions should be borne in 

 mind, in order that the most profitable results may be 

 secured." (See notes on fertilizers in Chapter XXI.) 



log. Dangers of excessive applications. — When ap- 

 proved methods of soil management are followed, prac- 

 tically no danger attends the use of large amounts of 

 commercial fertilizers. If the amount of vegetable mat- 

 ter decreases and the soil acidity increases, several diffi- 

 culties may develop. The soil may become hard and un- 

 productive, not because of large applications of fertilizers, 

 but because of small additions of humus. With the 

 continued application of large quantities of mineral ferti- 

 lizers the soil may become extremely acid, when legumi- 

 nous cover or green manurial crops cannot be grown 

 successfully. Malnutrition diseases sometimes develop in 

 strongly acid soils, especially if humus is deficient. 



The causes and the control of malnutrition disease have 

 been studied by the Virginia Truck Experiment Station. 

 When the disease is present the following symptoms may 



