30 



An acre of dent corn yielding 15 tons green, with 25 per cent dry 

 matter (equal to 3| tons), would use during its period of growth 

 10.6 inches of water. As shown in the table of rainfall previously 

 given the average rainfall for the past fourteen years from about 

 twenty localities in Connecticut for the months of June, July and 

 August is only 11.3 inches. 



Of course, no account is made here of water lost by leaching. 

 The one important lesson that these results do point out is the large 

 amount of water used in the growth of plants and the need of con- 

 serving the stores in the soil, or of adding an artificial supply 

 when the rainfall is below the average. We know of no extensive 

 experimentr showing the amount of water used by small fruits, but 

 all crops which produce a heavy growth of foliage transpire moist- 

 ure rapidly. A crop like strawberries, which makes a heavy growth 

 of both foliage and fruit in about two months, must use immense 

 quantities of water. 



The discussion of the large amounts of water used by plants 

 naturally leads to the consideration of the losses of moisture from 

 the soil. Only a part of the water which falls becomes avail- 

 able to growing crops. A considerable part flows off on the sur- 

 face of the ground and finds its way into streams, while in the 

 case of heavy rains quite a portion is leached away and carried 

 beyond the roots of plants. However, in soils that are not too 

 porous much of the water which is leached into the lower strata 

 may find its way back to the surface soil by capillary attraction. 

 One of the most important matters to be considered in the culture 

 of crops is that a large and variable quantity of water is evapo- 

 rated directly from the soil. The amount of this depends upon 

 several conditions, the chief of which are the state of the weather, 

 the kind of crop on the soil, the amount of cultivation, and whether 

 or not the soil is mulched. In times when rainfall is insufficient 

 for the best growth of crops the atmospheric conditions are usually 

 such as to favor the evaporation of moisture from the soil. The 

 amount of evaporation that takes place depends upon the amount 

 of wind that may be blowing over the soil and the degree of satura- 

 tion of the air. Meteorological data showing the relative humidity 

 of the air indicate that on hot, dry days the air may contain as low 

 as from 20 to 50 per cent of its water-holding capacit}'. Under 

 such conditions, especially in connection with winds, the moisture 

 evaporates from the soil very rapidly. The shade aiJorded by 

 crops like grass and small grains tends to lessen the amount of 

 evaporation from the soil, while crops which do not shade the 

 ground as much furnish conditions more fav'orable for the escape 

 of moisture. 



