WINTER INJURY 



283 



Table 25. — Mean Efficiency of Windbreaks in Area of Greatest 

 Protection {After Bates^^) 



break are of particular interest. Table 26, arranged from his report 

 of determinations made November 5, shows a difference well worth 

 consideration, particularly as they were made at the approach of winter. 

 Assuming, as Card does, that soil moisture up to 10 per cent, is not 

 available for plants, the average available moisture up to a distance of 

 about 7 rods was 2.55 per cent.; beyond that point it was 0.65 per cent. 



Table 26. — Soil Moisture at Varying Distances from a Windbreak^' 



The area protected by a windbreak is variable. It has been stated 

 that in the Rhone valley each foot in the height of a windbreak protects 

 plants for 11 feet to the leeward. ^^ From rather general observations in 

 Iowa and Nebraska it has been estimated that a rod of ground is sheltered 

 for each foot in height of the windbreak, and other estimates state that a 

 windbreak 25 feet in height will protect 10 rods of orchard. Bates 

 found that the area extended on the average not more than 20 times the 

 height of the windbreak; at this distance the wind velocities were found 

 to be almost as great as on the windward side. Card's soil moisture 

 determinations indicate that for this windbreak the effects were not 



