July, 1917.] GROWTH OF APPLE TREES. 5 



is affected by several external factors and also by intrinsic factors. 

 The temperature records here given, however, do not deal with the 

 causes for or factors which have brought about the temperatures 

 recorded but rather are offered as a statement of what tempera- 

 tures obtained in the soil of the various cultural plots. Since air 

 temperature is the most potent factor in determining the soil 

 temperature it is herein used for comparison. 



RELATION OF AIR AND SOIL TEMPERATURES. 



The soil is probably affected to a greater extent by the tem- 

 perature of the air than by any other external factor, and the 

 nature or amount of soil covering seems to be the greatest factor in 

 influencing the degree to which the soil will respond to the changes 

 in the air temperatures. From Chart No. 1 it can be seen that the 

 temperature of the soil changes in the same direction as the air 

 temperature but does not respond immediately and can be seen on 

 the day following rather than on the same day. This follows 

 pretty consistently across the chart. This is brought out more in 

 detail below. 



EFFECT OF CULTURAL TREATMENTS ON SOIL TEMPERATURE. 



By examining Table No. 1 and Chart No. 1 it will be seen that 

 there is not a great variation in the temperature of the various 

 plots at any one time. While there is a little difference in the 

 soil at the two ends of the orchard it can be assumed that that 

 fact would not account for much variation in temperature, for- 

 according to Bouyoucos, there is little difference throughout the 

 summer between the various soil types and the variation in soil 

 type is much less marked in this orchard than in the kinds with 

 which he worked. 



The plots under observation have been treated as follows since 

 the spring of 1908: 

 Plot 1. Permanently in sod. 



Plot 4. Clean Cultivation each year (no cover crop). 

 Plot 5. Cultivation with a cover crop. 

 Plot 7. Same as Plot 5, but an application of complete fertilizer 



is applied each spring. 



Plot 9. Same as Plot 7, except the complete fertilizer in this case 

 is higher in nitrogen than in Plot 7, 



