210 THE PRINCIPLES OF SOIL MANAGEMENT 



than is desired, will cause the soil to break up into a 

 much better condition than if the surface had not been 

 treated. The width of the disk or harrow makes it 

 possible to cover a large area in a short time, and 

 thereby considerably lengthen the period during which 

 plowing can be satisfactorily done, as well as conserving 

 moisture for the succeeding crops. 



To summarize briefly the cardinal points in mulch 

 control: (1) They are more effective and more easily 

 maintained in an arid than in a humid climate. (2) Their 

 efficiency depends directly on their dryness and fineness. 

 (3) Sandy soil is more easily maintained as mulch 

 than clay soil. (4) From two to three inches is ordi- 

 narily the most effective depth. (5) After heavy rain, 

 the soil mulch must be renewed by tillage, and this is 

 much more urgent on clay than on sand soil. Even 

 without rain, a clay mulch may become inefficient. 

 (6) Tillage for mulch purposes must ordinarily be more 

 frequent in the spring, or humid season, than at other 

 times of the year. (7) The use of foreign materials 

 as mulch may be justified under special circumstances. 



97. Fall and spring plowing. Fall and early spring 

 plowing owe much of their efficiency to the conservation 

 of moisture effected through the creation of a mulch 

 over the surface. Fall plowing may be practiced for 

 a number of reasons, but in regions of deficient rainfall, 

 particularly in the winter, the conservation of the mois- 

 ture in the soil at the close of the growing season is an 

 important consideration. This practice is well adapted 

 to those soils in the semi-arid section that do not blow 

 too badly when fall-plowed, and where the winter rain 



