60 ELEMENTARY AGRICULTURE 



tion of this capillary water. The simplest way to get 

 this blanket spread over the soil is to cultivate it. The 

 layer of cultivated soil dries out very rapidly, but it 

 prevents the air from getting at the moist soil under- 

 neath, and thus keeps it from drying out. It acts as a 

 sort of dry blanket to prevent the evaporation of mois- 

 ture. 



Summary. There are three chief reasons for till- 

 ing the soil : ( i ) To pulverize it, making it easy 

 for the plant roots to penetrate it in every direction 

 and to get at the store of food it contains. (2) To stir 

 it and thus hasten the solution of plant food as well as 

 to destroy weeds that rob the plants of their food. 

 (3) To form a soil mulch, a sort of "dry blanket," 

 which will prevent rapid evaporation of the capillary 

 water from the soil. 



Free Bulletins, U. S. Dept. of Agriculture. 

 No. 306. Some Soil Problems for Practical Farmers. 

 Problems. 



1. How many square feet in one square yard? In 

 one acre? 



2. If soil is cultivated to the depth of 4 in., how 

 many cubic feet of cultivated soil per acre? How 

 many, if cultivated to the depth of 6 in.? If culti- 

 vated to the depth of 8 in. ? 



3. How much more plant food is made available 

 with cultivation to the depth of 8 in. than with a 4 in. 

 depth of cultivation? 



