150 



SOILS AND FERTILIZERS 



sometimes higher than the average temperature of the at- 

 mosphere, or even than the maximum air temperature. The 

 soil below is cooler and continues to decrease in temperature 

 as the depth increases. For that reason a cellar is usually 

 cooler in summer than is the outside air. On the other hand, 

 the soil does not become as cold as does the atmosphere in 

 winter, and below a few feet, in temperate regions, the soil 

 does not freeze. The following table gives the mean atmos- 

 pheric temperatures, and the soil temperatures, at different 

 depths by months throughout an entire year. 



Table 33. — Average Monthly Temperature Readings Taken 

 at Lincoln, Nebraska 



January . 

 February 

 March 

 April . . 

 May . . 

 June . . 

 July . . 

 August . 

 September 

 October . 

 November 

 December 

 Average 

 Range 



Average op Twelve Years 



Air 



25.2 

 24.2 

 35.8 

 52.1 

 61.9 

 71.0 

 76.0 

 74.5 

 67.6 

 55.5 

 38.7 

 28.3 

 50.9 

 51.8 



3 Inches 

 Deep 



27.8 

 27.3 

 37.2 

 56.0 

 67.5 

 78.0 

 83.6 

 81.3 

 73.4 

 58.4 

 40.9 

 31.4 

 55.3 

 56.3 



12 Inches 

 Deep 



31.2 

 30.2 

 35.4 

 49.3 

 60.7 

 69.9 

 75.7 

 75.7 

 69.2 

 57.8 

 44.7 

 35.2 

 52.9 

 45.5 



36 Inches 

 Deep 



38.5 

 35.5 

 35.8 

 43.8 

 53.3 

 61.3 

 67.4 

 69.8 

 67.6 

 61.3 

 52.2 

 43.3 

 52.5 

 34.3 



195. Factors that modify soil temperature. — There are 

 a number of conditions that exert an influence on the tem- 

 perature of the soil, important among which are (1) the 

 moisture content, (2) the color of the soil, (3) the slope of 

 the land. 



