52 



WINDBREAKS. 



total rainfall for the year is not over 25 inches, and where, therefore, 

 the demand can not be supplied. The result is poor plant growth. 



How much better will be the growth of the plants if the evapora- 

 tion is reduced by the presence of a good windbreak to 50, or even 40, 

 per cent of the normal amount ? The 28 inches, then, demanded from 

 the field crop will be scarcely more than the annual precipitation. 

 A good windbreak 100 feet high and one-half mile long will reduce by 

 32 per cent the evaporation from 73 acres, and thus decrease the 

 possible loss of moisture from 56 inches to 39 inches, where the mean 



2/0 



100 



70 



Z 3 



S 6 76 



3/0 



LEEWARD 



DIAGRAM 23. Protective efficiency of mulberry hedge. For wind velocities of 10 miles per hour. 

 A, two rows, road between, height 24 feet; 16 readings. B, single row, height 32 feet; 6 readings. 



wind velocity is 10 miles per hour. By such protection the water 

 supply of the field may be retained until long after unprotected fields 

 have become dry. 



Relation to crops. Since the season of 1908 was unusually wet, 

 there was no serious drought damage. In the spring there was a 

 slight drought, which affected sprouting corn and considerably 

 reduced the stand in fields of small grains. The plants which sur- 

 vived, however, later obtained an abundance of moisture, so that a 

 moderate crop was harvested. Corn was not much damaged before 

 the rains arrived, but it is probable that a part of the later-observed 



