644 



FUNDAMENTALS OF FRUIT PRODUCTION 



However, as a rule, low lying land is more subject to frost than that 

 somewhat elevated above surrounding or adjoining fields, though there 

 are certain exceptions which are discussed later. 



The dilTerence in temperature between two points, one of which is 

 50 or 100 feet above the other, of course depends on many factors, such 

 as general lay of land, relative areas of the land having the respective 

 elevations and proximity to bodies of water. However, the inequality 

 in temperature, particularly on quiet nights, in spring and fall when 



64^ 



2P.M. 4P.M. 6P.M. 8P.M, 10P.M. MDT. Zh.M. 4AM. 6A.M. 8A.M. 10A.M. 

 Fig. 67. — Continuous records of the temperature from 4 p. m. to 9 a. m. at the base and 

 at different heights above the base of a steep hillside, showing the great differences in 

 temperature that sometimes develop on a clear, still night. Although the temperature at 

 the base was low enough to cause considerable damage to fruit, the lowest temperature 

 225 feet above on the slope was only 51°F. Note that the duration of the lowest tempera- 

 ture was much shorter on the hillside than at the base. (After Batchelor and West"^) 



there is greatest danger from frost, between points only a few dozen feet 

 apart in elevation is often considerable — often enough to make the 

 difference between no frost or a very light frost and a killing frost. Fig- 

 ure 67 shows graphically the diversity in minimum temperature that 

 sometimes occurs with variations in elevation of 25, 50 and 225 feet. 

 In this case a disparity of only 25 feet in elevation was accompanied 

 by a difference of approximately 5°F. between 8:00 p.m. and 8:00 a.m. 

 and an inequality of 50 feet was accompanied by a variation of 15° 

 to 20°F. At greater elevations the temperature was still higher, though 

 its rise was not proportional to the increase in height. 



This suggests that extreme divergencies in altitude, therefore, are 

 likely to afford much greater security from frost than moderate differences, 

 very slight inequalities, even of only a few feet, often are associated with 

 a sufficient variance in temperature to result in crop safety or crop loss. 

 Perhaps more nearly average differences in minimum temperature due 



