so 



DRY-FARMING CONGRESS, WICHITA, 1914 



The beneficial effects of windbreaks are brought about in several ways. 

 First, is the protection from occasional violent windstorms, which may 

 blow down grain crops and render them practically worthless. The direct 

 protection from wind and its mechanical effects is, of course, greatest 

 near the belt of trees, but is appreciable for a distance equal to 20 times 

 the height of the trees. Thus a windbreak 50 feet high would have some 

 influence on wind velocities and forces for a distance of 1000 feet to the 

 leeward. 



Closely connected with the protection exerted by windbreaks is their 

 direct influence on the supply of ground water available for agricultural 

 purposes. It is a well known fact that evaporation from any moist sur- 

 face is carried on at a rate about proportionate to the rate of move- 

 ment of air over that surface. Consequently, in checking wind velocities 

 the windbreak also checks evaporation. In the study above referred to 

 it was found that exceptionally heavy windbreaks might, at times, reduce 

 the evaporation at points to the leeward by as much as 70 percent of that 

 occurring in unprotected situations. This simply means that the crops 

 growing under this protection had nearly three times as great a moisture 

 supply as those growing in the open. This, of course, extends only over 

 a limited area, and under ordinary conditions the average saving in evapo- 

 ration over the entire area protected would probably not exceed 20 percent. 

 This, however, is of great importance when the moisture supply goes so 

 low that a small amount means the difference between life and death of 

 the crop. 



Another influence of windbreaks was found to consist in the creation 

 of higher day temperatures, and lower night temperatures within the zone 

 in which the air was calmed. This resulted, in all cases examined, in an 

 acceleration in growth, as though the crop had been placed under hothouse 

 conditions. The benefit was especially marked in the case of corn crops. 



It is true, of course, that any belt of trees growing next to a field 

 crop, robs that crop more or less of moisture and sunlight. This, how- 

 ever, has been taken into consideration, and the conclusion has been reached 

 that any windbreak of reasonable width will more than pay for the 

 ground that it thus occupies, through its effect in preventing evaporation, 

 etc. In this way the windbreaks in one county, such as the heavily- 

 planted counties of eastern Kansas, save thousands of cubic feet of water, 

 which otherwise would be lost to crops, each year. 



We have seen, now, that forests may have several different influences 

 on the question of agricultural water supply. They may help the irriga- 

 tor by holding back the spring mountain freshet and making the water 

 available when most needed; they may prevent erosioli, which increases 

 the severity of floods and frequently destroys the fertility of valuable 

 farm lands; and finally they may help any farmer, when planted judici- 

 ously, in protecting his fields from excessive evaporation. Nature has 

 placed these friends of man in almost all regions which are fit for human 

 occupancy, and we should be indeed careful not to disturb nature's bal- 



