THE TILLAGE OF SOILS 39 



then that clay soils need green and barnyard manures 

 more than sandy ones as far as structure is concerned? 

 Which of all these soils could be plowed first after a rain? 



Fig. 11. — Adding organic matter to the soil. 



26. One Cause of Cloddy Fields. — The next experi- 

 ment will bring out one of the common causes of the 

 cloddy fields which often prove troublesome to farmers. 



EXERCISE 17 



Object. — To study the effect of stirring or tramping 

 soils when wet. 



Procedure. — Make three groups of mud pies out of 

 clay, silt and sand ; or use types of soils from the fields in 

 which these materials predominate. Each group is to 

 consist of one pie of clay, one of silt and one of sand. If 

 the soil is brought from the field, it will probably be moist 

 enough for the pies of the first group. If the soil is dry, 

 add just enough water to moisten and put it in the con- 

 dition of well tilled land. To each pie of the second 



