II.] SOOT 69 



foundly modified by its physical condition. In the first 

 place, the dark colour of soot makes it a very effective 

 absorbant of the sun's rays, so that in sunlight the tem- 

 perature of land which has been darkened by a sprinkling 

 of soot will rise two or three degrees above that of 

 the same land uncoloured. And as the radiation from 

 such darkened soil at low temperatures is not increased 

 in the same proportion, there is no corresponding loss 

 of heat at night from the sooted land to discount its 

 higher temperature by day. Soot is most commonly 

 used by farmers as a top dressing for wheat and other 

 spring corn ; these crops are particularly responsive 

 to a small application of active nitrogenous manure 

 in the early months of the year when the soil is cold 

 and the oxidation of its nitrogenous residues is slow, 

 hence part of the value of the soot. At the same time, 

 the increased temperature of the soil induced by the 

 black colour of the soot is particularly valuable in 

 forwarding the growth both of the plant itself and of 

 the bacteria which are rendering available the reserves 

 of plant food in soil. 



Soot also helps materially to lighten the texture of 

 heavy soils, and on that account is much valued by 

 market gardeners in districts like Evesham, where the 

 land is somewhat clayey and retentive. 



Soot is also very distasteful to the slugs and small 

 snails which often do great damage to cereal and other 

 crops in their earlier stages. 



Soot is usually sold by the bushel, which weighs 

 about 28 lbs., and the lighter the soot is per bushel 

 the more it is valued, because this indicates its purity 

 and freedom from ashes or other admixture. This is 

 probably the best test the farmer can apply, for soot 

 being bought locally no guarantee can be obtained as 

 to its composition, nor could one very well be given, 



