6 



FARMERS' BULLETIN 788. 



usually plows, cultivates, and mulches with the object of conserving 

 every drop of water that may reach the soil during the year. In the 

 " dry-farming" regions of the West these conservation measures are 

 carried farthest. Here it may be necessary to save the moisture of 

 two seasons to grow a single crop. 



Anything which helps to conserve the moisture of the soil is of 

 direct benefit to the farmer. The windbreak has this effect in a 

 marked degree. The drying power of the wind is reduced by the 

 windbreak very nearly in the same proportion as its velocity. In the 

 immediate lee of the most effective windbreaks evaporation is re- 

 duced as much as 65 per cent. Farther from the trees the 



FIG. 3. Alfalfa grows almost to the base of honey-locust trees. 



reduction is less. The amount of reduction depends not only 

 upon the density and proximity of the windbreak, but upon 

 whether the field is fallow or in crops. The saving in moisture is 

 least when the field is fallow, so that the only reduction is in the 

 direct evaporation from the soil; it is greatest when the field is in 

 crops, so that there is a reduction not only in the direct evaporation 

 from the soil but also in the evaporation from the leaves of the crops. 

 The more frequently winds occur in any locality during the grow- 

 ing season, and the greater their velocity and drying power, the more 

 important it is to use every means of preventing evaporation. Wind- 

 breaks are especially valuable, therefore, in the Middle West, where 



