294 



SOIL PHYSICS AND MANAGEMENT 



area, it is radiated into space much more rapidly because of the 

 small amount of vapor in the air to hold it. 



2. Precipitation. When warm rain falls upon and penetrates 

 the cold soil it carries with it large amounts of heat. This may 

 account for the rapid growth of plants after a shower in spring. 

 An inch of rain 10 degrees warmer than the soil would raise the 

 temperature of the surface six inches of soil 4.6 degrees if 10 per 

 cent of moisture existed in the soil to begin with. 



3. Chemical changes in the soil result in the production of 

 heat. This is especially true of all chemical changes in organic 

 matter, but particularly so of green crops and fresh farmyard 

 manure. The results of some experiments at the Imperial College, 

 Tokio, Japan, with different amounts of manure applied and thor- 

 oughly mixed with the soil, are given for five-day intervals in the 

 accompanying table: 



Influence of Farmyard Manure on Temperature of Soil. 1 Degrees Fahrenttrit 



It will be noted that the heavier the application the greater the 

 increase in temperature. 



4. Physical Changes. When a soil absorbs water its tempera- 

 ture is increased. This is true for both water vapor and liquid 

 water, the former producing the highest temperature because of the 



Increase in Temperature by Absorption of Water Vapor at 86 Degrees F. 

 (SO Degrees C.) 2 



Quartz sand 1.58 F. ( 0.88 C.) 



Calcium carbonate (precipitated) 2.64 F. ( 1.47 C.) 



Kaolin 4.73 F. ( 2.63>C.) 



Hydrated ferric oxide 16.74 F. ( 9.30 C.) 



Peat.. ... 22.05 F. (12.25 C.) 



