THE CONTROL OF SOIL MOISTURE 



279 



(4) from two to three inches is ordinarily the most effec- 

 tive depth; (5) after a heavy rain, the soil mulch must 

 be renewed by tillage, and this is much more urgent on 

 clay than on sandy soil ; even without rain, a clay mulch 

 may become inefficient; (6) tillage for mulch purposes 

 must ordinarily be more frequent in spring or during 

 periods of heavy rain, than at other times of the year; 

 (7) the use of foreign materials as mulches may be justi- 

 fied under special circumstances. 



197. Water saved by a mulch. — It is very difficult 

 to quote data regarding the capacity of a mulch to con- 

 serve moisture, since conditions vary to such a degree 

 from one region to another. Again, water may not be the 

 limiting factor in crop growth, and even if moisture were 

 saved there might be but little influence on crop yields. 

 As a general rule, mulches are most easily maintained 

 and most effective in arid and semiarid regions. Since 

 there is no doubt that moisture, under such conditions, is 

 the limiting factor in plant growth, data from such regions 

 should be especially significant. 



Moisture Content of Mulched and Unmulched Eastern 

 Montana Soils. Average of Three Years. 1 October 6 



1 Buckman, H. O. Moisture and Nitrates in Dry Land 

 Agriculture. Proc. Amer. Soc. Agron., Vol. 2, p. 131. 1910. 



