THE NATURE OF SOIL 35 



tural value and has an important influence on its 

 temperature. A dark-coloured soil is usually 

 warmer and earlier than a light-coloured soil. All 

 dark substances absorb more of the sun's rays 

 than light substances. That is why we wear light- 

 coloured clothes in summer, and partly why snow 

 melts faster on the dark-coloured, plowed ground 

 than on the meadow. In Switzerland farmers some- 

 times hasten the disappearance of the snow by strew- 

 ing it with black, powdered slate. Gardeners some- 

 times sprinkle a light-coloured soil with peat, 

 charcoal and bog mould; these are called "sun 

 traps." Melons are ripened in Saxony with the aid 

 of a layer of coal dust. But although colour has 

 an important influence on the power of a soil to 

 absorb heat, it has not ability to retain heat. Schub- 

 ler states that, other things being equal, a dark- 

 coloured soil is about 8 warmer near the surface 

 than a light-coloured soil. 



This difference in the temperature of soils, due to 

 colour, may have a marked influence upon the 

 growth of a crop, especially on its germination. 

 When earliness is a prime consideration, as it is 

 with most market-garden crops, the colour of a 

 soil may become very important. Dark, sandy 

 loams, rich in humus, are preferred by market 

 gardeners. Light-coloured soils may be made 

 dark by filling them with humus. Two or three 

 green-manuring crops plowed under will darken a 

 light-coloured soil quite noticeably. I have a 

 neighbour who, in three years, has transformed a 

 poor, yellow soil into a black, retentive and pro- 

 ductive loam by plowing under four inches of com- 

 posted manure every fall. Another neighbour, 

 under similar circumstances, has accomplished 

 nearly as good results by plowing under muck 



