16 AGRICULTURE FOR COMMON SCHOOLS 



These colors are generally caused by some chemical element 

 in the soil, usually some form of iron. Loams and mucks are 

 always dark colored, owing to the large amount of organic 

 matter in them. We shall see that color has something to do 

 with the temperature of a soil. 



Temperature. — The temperature of a soil is very im- 

 portant, since it influences the sprouting of seeds and the 

 growth of plants. Most farm seeds germinate best at tem- 

 peratures between 70 and 80° F. Furthermore, their best 

 growth takes place at temperatures equally high. Such seeds 

 and plants as corn, melons and cucumbers require even higher 

 temperatures. Dark colored soils are warmer than light 

 colored, because the dark color absorbs more heat from the 

 sun. Such a soil may be, according to Professor Brooks, of 

 the Massachusetts Agricultural College, as much as eight 

 degrees warmer during the hours of sunshine than a light- 

 colored soil. A soil which has rather coarse grains will warm 

 up more quickly than one having very small grains, because 

 the coarse particles will draw the heat from the sun better 

 than fine ones. This is one reason why sandy soils are 

 warmer than others and are desirable for early vegetables. A 

 dry soil is warmer than a wet one, hence drainage aids in 

 warming a soil. A soil having a good deal of humus in it 

 will tend to be cool because the organic matter holds water. 

 However, the dark color of such soils by absorbing heat has 

 a tendency to offset the cooling effect of the water. When 

 land slopes to the east, south, or south-west, it is naturally 

 warmer than land which slopes to the north or north-west, 

 because the sun's rays fall more nearly straight on it. 



Aeration. — It is necessary for the good of the plant that 

 air circulate through the soil. The air furnishes oxygen to 



