34 THE OLIVER PLOW BOOK 



is permitted to evaporate. The evaporation of moist- 

 ure is determined by the kind of soil, its compactness, 

 the amount of surface exposed to the rays of light, and 

 the wind. The greatest difference in temperature 

 between the different types of soil takes place in the 

 early spring thawing and the period immediately follow- 

 ing. This is of utmost importance to farmers especially 

 at planting time because a small amount of difference 

 in the temperature of the ground means speeding up or 

 retarding the rate of germination of the seed and the 

 growth of the plants. Other things being equal, it 

 logically follows that the sandy types of soil can be 

 planted earlier in the year than the clay types. 



When' a soil is cultivated a larger area of its surface 

 is exposed, thus the amount of evaporation is very much 

 greater. The result of greater evaporation is that the 

 temperature of the cultivated soil rises much higher and 

 faster than that of the uncultivated, and permits earlier 

 planting. This is one of the strongest arguments for 

 fall plowing and leaving the ground rough. In the 

 spring of the year the additional exposed surface dries 

 out much more rapidly and thus permits earlier seeding. 

 The most interesting part of this process is that as soon 

 as a dry mulch of this earth is formed on the plowed 

 soil the loss of water by evaporation is reduced very 

 much, while the loss on the unplowed soil is still greater. 

 In the summer this reduces the temperature of the 

 mulched ground, while that of the unplowed ground is 

 considerably raised. 



A further observation is that the heat which is not 

 utilized in the evaporation of water is being rapidly 

 conducted downward in the unplowed ground, thus 

 causing it to dry out at great depth. On the cultivated 



