42 Effective Farming 



the flow of water is decreased, consequently it has more time 

 to soak into the soil. Moreover the decreased flow tends to 

 lessen the amount of surface soil washed from the field. In 

 many sections of the United States, the lack of proper terracing 

 results in excessive soil washing, which becomes so serious in 

 neglected or improperly farmed areas as to ruin fields. The 

 result of excessive soil washing is pictured in Fig. 16. 



Reducing percolation losses. The loss of water and soluble 

 plant-food by percolation is greater in sandy soils, especially 

 if they have an open subsoil, than in those of finer texture. To 

 prevent this loss, the surface should be compacted with a roller 

 or a subsurface packer. This has a tendency to reduce the rate 

 of percolation of the water. It also reduces the size of the pore 

 spaces, which increases the water-holding capacity of the soil. 



Reducing evaporation losses. In humid climates it has been 

 found that evaporation during the summer months may be 

 as great as seventy-five per cent of the rainfall. This ex- 

 cessive loss of water can be reduced by providing a mulch on 

 the surface. A mulch is a protective covering on the soil 

 made for. the purpose of preventing loss by evaporation. It 

 may be either artificial or natural. 



An artificial mulch is formed by spreading some such material 

 as manure, straw, leaves, sawdust, and the like, over the sur- 

 face of the soil. Mulches of this kind are very effective in re- 

 ducing the loss due to evaporation, but their use is practicable 

 only for small areas of high-priced crops, such as strawberries, 

 bush-fruits, and some few kinds of vegetables. 



A natural mulch is formed by tilling the surface of the soil 

 itself. This produces in the surface layer a loose, open struc- 

 ture that obstructs capillary action. Such soil mulches are 

 very effective in reducing the loss of soil moisture by evapora- 

 tion. In humid regions and in arid regions where dry-farming 

 is practiced, from two to three inches has been found the best 

 average depth for soil mulches. In arid regions where the soil 

 is irrigated, a greater depth can be used. For fruits a depth 



