38 ELEMENTS OF FARM PRACTICE. 



practical way of adding nitrogen to the soil is to grow"'clover 

 and other legume crops. Most soils, in fact nearly all soils, 

 have enough potassium. Phosphorus is the element most 

 likely to be needed and the cheapest way to supply that is 

 to buy a fertilizer containing only phosphorus. 



Animal Manure. — Except in the case of soils that may 

 be seriously impoverished of some particular element of plant 

 food, it has been found that the total crop products from 

 fields that have received animal manure exceed those from 

 land treated with commercial fertilizers or which were not 

 manured. Animal manure is preferable because 



(1) it is produced at a minimum of expense, 



(2) it adds immediately available plant food to the soil, 



(3) it provides humus and acid solvents that assist soil 

 decay, 



(4) it produces effects for years after application. 



Questions: 



1. Describe the most practical means of maintaining a supply of 

 nitrogen in a soil for ordinary farming. 



2. Which of the four elements named in this lesson is most 

 likely to become exhausted? How may it be replenished? 



3. Is much potash removed from soil with ordinary crops? Why? 



4. What is a complete fertilizer? Is it usually economical? 



5. What are the advantages of animal manures? 

 Arithmetic: ' 



1. If 50 bus. of corn remove 31 lbs. of nitrogen, 6.1 lbs. of phos- 

 phorus, and 9.6 lbs. of potassium, how much would it cost to replace 

 these elements at 18c. per lb. for nitrogen, and 6c. per lb. for potas- 

 sium and phosphorus? 



2. If an acre of normal soil contains 4,000 lbs. of nitrogen, 2,000 

 lbs. of phosphorus and 35,000 lbs. of potassium, what is the total 

 value of these elements per acre at prices used in Example 1? 



3. If acid phosphate contains 6% phosphorus and a 50-bu. 

 crop removes 6.1 lbs. of phosphorus, how many pounds of acid phos- 

 phate would one have to apply to supply the needs of the crop? 

 Exercises: 



1. Find some field or fields in the neighborhood to which some 

 kind or kinds of fertilizers have been applied. Make note of the kind 

 of fertilizer used and, if possible, find a field part of which was fertil- 

 ized and part unfertilized. Note the growth of the crop on the fer- 

 tilized and also on the unfertilized part. Compare the color and 

 height of plants, also the thickness of growth and, if possible, find out 

 the yields on both parts of the field. 



2. Ascertain the contents of the commercial fertilizers offered 

 in your market and compare their values with prices asked for them. 



