Soils 43 



as great as ten or twelve inches is effective. For shallow-rooted 

 crops the depth must, of course, be decreased. Spike-tooth 

 harrows and weeders (paragraphs 223 and 225) are satisfactory 

 implements for forming mulches. After a rain the soil mulch 

 must be renewed, especially on a heavy soil, because the rain 

 has reestablished capillary communication between the lower 

 layers of the soil and the surface. The mulch breaks up this 

 communication. 



In the so-called dry-farming that is practiced in the semi-arid 

 regions of the West, a soil mulch is maintained throughout the 

 whole 3^ear to conserve moisture from the previous summer 

 and winter as well as that of the crop-producing season. In 

 humid regions soil mulches are very effective during dry periods 

 in summer. In the case of hoed crops, they may conserve 

 enough moisture to keep the plants growing normally during 

 the periods of drought. Often the conserving of water for the 

 use of plants during such periods may be an important factor 

 in the crop result. During a drought in southern Illinois a 

 few years ago, the author was shown two corn fields side by 

 side ; one was suffering for the want of water and the other 

 was thrifty and apparently well supplied with moisture. He 

 was told that the only difference in the treatment of the fields 

 was that one had been properly tilled to form a soil mulch and 

 the other had not. 



Soil mulches, in addition to conserving moisture, improve the 

 physical condition of soil and, as a result, increase its water- 

 holding capacity, thus preventing losses due to run-off and 

 percolation. The tillage removes weed growth, which means 

 not only a saving of the plant-food that the roots absorb, but 

 also the moisture. 



Improving soil structure to increase soil-water. By practicing 

 suitable tillage and by adding humus-forming matter, soil 

 structure may be improved to increase the moisture-holding 

 capacity. A clay soil, if worked at the proper time, is made 

 more granular, and put into condition to retain more water. 



