328 MAN'S USE AND CONSERVATION OF SOILS 



Keep a record of the loss of weight of each. Why have they lost 

 weight? How do the grass, the sawdust, and stirring of the earth 

 affect the loss? Suggest ways to keep soils from losing their 

 moisture. 



In Experiment 99, it was seen that if a layer of grass 

 or sawdust was put on the top of the soil, the moisture did 



DRY FARMING IN EGYPT 



not evaporate so rapidly as it did when the soil was not 

 covered. The grass could have been replaced by shav- 

 ings, manure, or any substance which would protect the 

 ground from the sun and wind. Protections -of this kind 

 are called mulches. They are most frequently used around 

 trees, vines, and shrubs. It is impracticable to use them 

 extensively on growing crops. 



It was also found that soil water was not readily evapo- 

 rated where the top of the soil was kept stirred, so that 



