RESULTS OF MEASUREMENTS. 



65 



During most of the growing season the summation of diurnal and 

 nocturnal effects is a positive quantity, since a windbreak conserves 

 tin' heat of the protected zone. During the late fall and winter the 

 windbreak ass is is radial ion, and a general, more rapid cooling of the 

 soil results in the protected /one. 



EFFECTS OF ni;.vn\(; ON cuors. 



Acceleration of growth and increased yield. The effect of the super- 

 heating of air arid soil in the /one protected by a windbreak is favor- 

 able to crops which must begin, their growth at a time when the heat 

 is barely sufficient for germination, and it probably continues in a 

 decreasing degree throughout the growing season. In other words, 

 a windbreak produces hothouse conditions on a large scale, and 

 since- it reduces evaporation at the, same time, its total influence is 

 clearly favorable to vegetation. On the other hand, a windbreak 

 may bo disadvantageous in spring if a drying out of the soils is de- 

 sired. 



The season of 1!H)S was especially favorable for noting the effect 

 of heating; it was apparent, in cornfields early in the season. The 

 higher temperatures in the protected /one caused earlier germina- 

 tion and more rapid growth than in the open. The following figures 

 on the height of plants in a cornfield to the north of a hedge of 

 usage orange, we.ro obtained on July S in western Kansas. The height 

 of the hedge was about 20 feet. The spring winds up to that time 

 had been mainly from the south. 



TA I;I,K \'2.Kli.m/:uit/ effect of windbreak protection in accelerating growth. 



A similar cornfield was noted on the north side of a dense, mixed 

 grove in Nebraska. The grove, which was about 38 feet high, 

 formed a complete harrier to the wind. The effects were here even 

 more marked. Late in June the average height of the corn in the 

 first is rows next to the windbreak was 4J feet, while beyond this 

 it was only about 2 feet. At the close of the growing season the 

 luxuriance of the vegetative growth next to the windbreak was still 

 markedly greater than in the open. At harvesting the weight of 

 the corn at the point of greatest protection was about 18 bushels per 

 acre greater than in the open, or 59 bushels per acre as against 41. 

 92290 Bull. 8611 5 



