664 STATE BOARD OF AGRICULTURE. 



EFFECT OF THE DECOMrOSITION OF MANURE ON SOIL TEM 



PERATURE. 



OBJECT AND METHOD OF EXPERIMENTATION. 



It might be said that the farm, soil receives its heat from four differ- 

 ent sources: (1) from the direct radiation of the sun; (2) from the 

 precipitation or condensation of aqueous vapor, (3) from the heated 

 interior of the earth by conduction, and (4) from the decomposition of 

 organic matter. The amount received from the last three sources is 

 very small; it is the first source that contributes the greatest, if not the 

 Avhole, of the warmth of the soil. The second and third sources are 

 entirely beyond the control of man ; the first can be controlled in an 

 indirect wav bv modifving the color and water content of the surface 

 soil ; the fourth is the only one of the four sources which is practically 

 entirely under the control of man, because he can add the organic matter 

 to the soil. 



The amount of heat liberated by the decomposition of organic matter 

 is considerable if the action is complete and rapid — it is equal to the 

 amount of heat of combustion. The decomposition process, however, as 

 carried on under field conditions is very slow and hence the amount 

 of heat given off is practically imperceptible. 



The principal sources of organic matter in the soil are (1) vegetable 

 matter and (2) animal manure. The first is practically unimportant 

 so far as heat is concerned because in the spring the temperature of the 

 soil is already sufficiently high enough for the germination of seed and 

 growth of i)lants by the time the vegetation has gro^-n large enough to 

 be turned under. In the fall the soil tempera-ture is also sufficiently 

 high for the germination of seeds and groNN'th of seedlings without the 

 necessity of increasing it. Furthermore, at either season the amount of 

 vegetation that can be turned under is so small in comparison with the 

 great bulk of the soil that the warming effect resulting from the decom- 

 position is practically nil. 



The extent to which the second source of organic matter may in- 

 crease the temperature of the soil will depend upon the freshness and 

 quantity of the material. The statements in different textbooks vary 

 upon this point. Some are to the effect that the decomposition of 

 manure of any kind has practically no importance on the thermal rela- 

 tions of soils; others, that the influence is quite appreciable. 



These statements or conclusions have been drawn from insufficient 

 data. The amount of experimentation that has already been done on 

 the subject is very meager. The most widely quoted work is that of 

 rjeorgeson-" who added 0.0, 10, 20. 40 and 80 tons of farm yard manure 

 to a soil and studied its temj)erature. The exjteriment was ])erformed 

 by mixing thoroughly the soil and the manure, placing the mixture in 

 wooden boxes without bottom and top and burying the latter in the 

 ground up to the surface edge. He found that the temperature of the 

 soil was increased with the increase of the application of manure. The 



" Agricultural Science 1:251. 



