4 BULLETIN NO. 161 



ture in the orchards increases and the chance of a killing frost 

 occurring becomes less. It has been suggested that the develop- 

 ment of buds be retarded either by piling snow about the base 

 of the tree, or by whitewashing it. The snow would have but a 

 very slight effect, if any, on the temperature of the tree branches 

 and would not sensibly change the temperature of the roots and 

 we, therefore, believe that treatment to be valueless. Although 

 the whitened surface of the tree would reflect a high percentage 

 of the energy that falls upon it, and would consequently absorb 

 a smaller amount, yet unless the light-colored material that is 

 applied is valuable as an insecticide, the method is of doubtful 

 value. 



Numerous devices for the prevention of frost injury have 

 been tried. Among the methods used are: Hanging small 

 kerosene lamps in the trees, drawing canvass around the trees 

 on a cold night for very valuable orchards, the drawing of 

 canvass over a permanent framework built above the trees and 

 for small plants, covering them with straw or paper and plowing 

 a furrow between the rows and thereby throwing the loose dirt 

 over the foliage. In some cases orchards are heavily irrigated 

 on the night of an expected frost and with reported success in 

 not a few cases. Spraying the orchard with water has been re- 

 commended. If the cost of producing the fruit is less, if the fuel 

 is cheap, and if there is an excellent market for the fruit so that 

 it will bring a high price, then it may be profitable to heat with 

 oil burners; but we do not think smudging without heating is 

 satisfactory. 



SOIL TREATMENT TO MODIFY MINIMUM AIR TEMPERATURE 

 (CONDITION OF GROUND AND ITS COVERING) 



The attempt has been made, and with some success, to treat 

 the soil in such a way as to prevent the minimum temperature 

 of the air above the ground from going as low as it otherwise 

 would do. The rate of loss of heat from the ground to the air 

 above during the night depends on the difference in temperature 

 between the air and the ground. The larger this difference, the 

 more rapid is the rate of heat transfer. The treatment consists 

 in lowering the heat capacity of the ground so that the same 

 amount of heat falling upon it in the day time will cause a larger 

 rise in temperature and therefore a larger amount of heat will 

 be given to the air by the ground during the hours when frost 

 is liable to occur. This has been successfully done by Professor 



