148 RELATIONS OF SOIL TO HEAT 



Although farmyard manure furnishes a considerable source 

 of heat when employed in a hot-bed, its application has little 

 influence on the temperature of farm soils. This is chiefly 

 owing to the small proportion of farmyard manure which 

 is mixed with the soil. The farmer also seldom applies the 

 manure in a fresh state ; a portion of its heat-producing 

 power is thus lost before it reaches the land. 



A few experiments were made by Georgeson at the Imperial 

 College at Tokio (Agricultural Science, i. 251) on the altera- 

 tion in temperature which followed the application of various 

 quantities of farmyard manure to the soil. The soil used 

 was peculiarly light and porous, being in fact a volcanic 

 ash. The manure was partly decayed, but still rather long. 

 The soil and manure were well mixed, and wooden frames 

 were filled with the mixture to a depth of i ft. ; one frame 

 received no manure. The frames were sunk in the open 

 ground, the top of each frame being level with the surface. 

 The experimental soils were thus under perfectly natural 

 conditions in respect to rainfall, drainage, &c. The average 

 temperatures of the soils, in successive five-day periods, are 

 shown in Table XXV. The temperatures are given in 

 Fahrenheit's degrees. 



The increase in temperature was greatest during the first 

 five days, and then rapidly diminished. After the first fifteen 

 days the increase became almost imperceptible where only 

 ten tons of manure per acre had been applied, but con-' 

 tinued to be distinct after twenty-five clays when forty and 

 eighty tons of manure had been employed. As an ordinary 

 dressing of farmyard manure does not exceed ten tons per 

 acre, and a very liberal dressing seldom exceeds twenty tons 

 per acre, it would appear that the rise of temperature pro- 



