THE USE OF FERTILIZERS 211 



A fertilizer based on the first percentages would be called 

 a 1-8-10 fertilizer ; one based on the second a 3-8-5 ferti- 

 lizer, and so on. In making up these formulas the carriers 

 to use are indicated in the previous discussion. The quan- 

 tities that it is desirable to use will depend so much on 

 the natural productiveness of the soil that it is not possible 

 to prescribe for soils in general. On soils of about average 

 productiveness, however, a certain range for each of the 

 classes of crops may be suggested. 



Legumes . . 100 to 200 pounds per acre 



Small grains 100 to 300 pounds per acre 



Vegetables 500 to 1000 pounds per acre 



Grass 200 to 500 pounds per acre 



Orchards 200 to 600 pounds per acre 



Roots . 300 to 800 pounds per acre 



269. Fertilizers for different soils. — The best way to 

 ascertain what fertilizers are needed for a particular soil is 

 to test it with different kinds and quantities of fertilizing ma- 

 terials. It will thus be possible to estimate whether the 

 three substances, nitrogen, phosphoric acid and potash 

 are all needed, and in about what quantities they should 

 be applied. 



A practical way is to select a level and apparently uniform 

 part of a field and on it lay off plats of land eight rods long 

 and one rod wide, giving an area of ^ of an acre. These 

 plats should lie parallel on their long side, but should have 

 a space of at least three feet between them. The arrange- 

 ment is shown in Fig. 31 on the next page, which also in- 

 dicates the quantity of fertilizing substance that each plat 

 should receive. 



The fertilizer used in this experiment is designed for small 

 grains, the mixture being 3-8-5 if the carriers contain about 

 15 percent nitrogen, 14 percent phosphoric acid and 48 per- 

 cent potash respectively. If a legume or grass crop is 



