34 ELEMENTS OF FARM PRACTICE 



Potassium is needed by all crops. It is especially 

 needed in hay crops, in the straw of grain crops, and in po- 

 tato and root crops. It is potassium that gives stiffness 

 to the straw of grain crops and enables it to stand up and 

 mature a crop. Where there is a scarcity of potassium the 

 straw of grain crops is likely to be weak. Potassium is 

 removed from the farm rapidly by such crops as 

 hay, potatoes and sugar beets. The amount of potassium 

 in ordinary soils varies from 20,000 to 50,000 lbs. per acre. 



Calcium is used in a very limited extent by plants, as 

 plant food, except by legumes, such as alfalfa, clover, peas, 

 etc. Its mo^t important use in the soil is to overcome 

 acidity or sourness. When a soil is sour, bacteria neces- 

 sary for the liberation of plant food are likely to be lack- 

 ing, especially those bacteria associated with the accumu- 

 lation of nitrogen in the soils and its conversion into forms 

 available for plants. A sour soil is often indicated by the 

 growth of such weeds as sorrel and horsetail fern, or by 

 its failure to produce good crops of legumes. It is also 

 easily detected by several simple tests. Many soils have 

 an abundance of lime, while others are seriously in need of 

 it. The amount of calcium in normal soils varies from a 

 few hundred pounds to a great many tons per acre. 

 Questions: 



1. What do you understand by the term fertilizer? By com- 

 mercial fertilizers? 



2. Name the four elements that are likely to be lacking in cul- 

 tivated soils, and tell at least one special purpose for which each is 

 needed. 



Arithmetic: 



1. If a soil contains 1,000 lbs. of phosphorus per acre, how many 

 100-bu. crops of corn can it produce, without the addition of more 

 phosphorus? If 1 bu. of corn removes 12-100 lbs. of phosphorus? 



2. If nitrogen is worth 18c. per lb. as a fertilizer, what is the 

 value of 2 tons of clover hay to plow under? If it contains 2 lbs. of 

 nitrogen per 100 lbs.? 



3. If a soil contains 50,000 lbs. of potassium per acre, how many 

 100-bu. crops of corn can it produce without exhausting the potassium, 

 if 1 bu. of corn removes 2-10 lbs. of potassium? 



FERTILIZERS AND THEIR USE 



Costs. — We have learned that there are four elements 

 needed by plants, nitrogen, phosphorus, potassium and 



