ORCHARD LOCATIONS AND SITES 643 



to drought than others. Fruit grown on northern or eastern slopes 

 therefore tends to average somewhat larger in size than that produced 

 on a southern or western exposure. In some sections the soil on many 

 southern slopes is much thinner than that on northern, eastern or western 

 exposures and in such instances a particular slope is to be avoided, not 

 because of the slope itself but because of the factors with which it is asso- 

 ciated. In much the same way certain slopes are to be avoided in certain 

 sections because of their exposure to prevailing winds. When land slopes 

 away from the direction of the prevailing wind considerable protection 

 is afforded the trees by the contour of the ground, but when it slopes in 

 the direction of the prevailing wind much more trouble is likely. 



Abruptness of Slope. — Gentle slopes are almost always preferable to 

 abrupt slopes. Many orchards on very steep hillsides have proved 

 profitable, but the cost of production under such conditions is likely to 

 be considerably higher than on more nearly level land of the same char- 

 acter. This of course assumes equally good soil and other conditions on 

 the steep and the gentle slopes. Different environmental conditions in 

 the two locations may reverse the situation. Thus, in the Piedmont 

 section of Virginia where the orchards are planted on steep hillsides and 

 where it is necessary to spray five to seven times, apples are produced at 

 a lower cost than in the Shenandoah valley where less spraying is required. 

 As a rule it is best to limit orchard planting to slopes so gradual that cul- 

 tivation may be practiced without great danger from erosion and over 

 which spraying machinery and other equipment may be hauled without 

 serious difficulty. The necessity of gentle slopes is still greater in sections 

 where irrigation is practiced. 



AIR DRAINAGE 



Fruit growing, more than almost any other branch of agriculture, 

 requires comparative freedom from untimely late spring and early fall 

 frosts; in turn the occurrence of frosts within certain limits is determined 

 largel}^ by what is commonly known as "air drainage," the settling of 

 cold air to lower levels. This is discussed in some detail in the section on 

 Temperature Relations. 



Influence of Elevation. — Many factors influence air drainage, some 

 to a very marked extent and others only to a comparatively small degree. 

 Probably the most important single factor in air drainage is elevation. 

 Height above adjoining land or fields usually is of greater significance 

 than absolute elevation above sea level. Frost is as likely to occur during 

 the danger period at the high elevations found in some of the intermoun- 

 tain fruit growing districts as at the low elevations of the seaboard. 

 Portions of the Ozarks with an elevation of over 1,000 feet are as frosty 

 as the Hudson River valley, which lies only a little above sea level. 



