EXPERIMENT STATION BULLETINS. 677 



ence in temperature at the lower depths, and (4) the effect of the dry 

 mulch of the cultivated soil. 



Salt solutions had a very marked influence on the rising and lowering 

 of soil temperature. Different salt solutions of the same density or 

 the same solution of different densities raised the soil temperature con- 

 siderably. Their influence was also very pronounced on the rate and 

 degree of lowering of temperature, as well as on the rate of thawing. 



The different kinds of manure raised the soil temperature differently, — 

 horse manure the most, sheep manure the least, and the cow manure 

 intermediate. In every case the greatest rise took place in the first 

 three or four days. The rise increased with the increase in quantity. 

 The degree of rise is probably insignificant for practical conditions. 



It is thus seen that the general subject of soil temperature is very 

 complex, that the number of factors influencing it is very large, that 

 the effect of these different factors may be direct or indirect, dependent 

 or independent, large or small, and that some of these factors can be 

 controlled and others cannot, for the final modification of soil tempera- 

 ture. 



