THE SOIL AS RELATED TO PLANTS. 93 



fertilizers required varies upon different soils 

 and for different plants.* 



The smallest amounts of direct fertilizers to 

 the acre, which will give satisfactory returns, are 

 10 pounds of nitrogen, 15 pounds of available 

 phosphoric acid, and 20 pounds of potash. By 

 comparison with the above table the amount of 

 the commercial fertilizer required may be ob- 

 tained. 



EXERCISE 3. How much nitrate of soda will be needed 

 for an acre if 10 pounds of nitrogen be required? (See 

 Table I.) 



How much sulphate of ammonia? 



How much dried blood (high grade)? 



How many pounds of tobacco stems? 



How many pounds of phosphoric acid and of potash 

 in tobacco stems which burnishes 10 pounds of nitrogen? 



How many pounds of bone-black superphosphate will 

 it take to furnish 15 pounds of available phosphoric acid? 

 How many pounds of insoluble phosphoric acid will 

 this bone-black contain ? 



How many pounds of sulphate of potash will it take 

 to furnish 20 pounds of potash? How much kainit ? 

 How much (unleached) wood ashes? How much phos- 

 phoric acid contained in the wood ashes ? 



For indoor plants, again, the amount of the 

 fertilizer must be governed by the kind of soil 

 and species of plant, for what is a "balanced 

 ration " J for one kind of plant is not for another. 



*" It is unsafe to use chemical fertilizers or liquid manures in 

 full strength on a heavy soil, which is not provided with suffi- 

 cient fibrous material." Year-book, 1902, p. 558. 



