282 SOILS: PROPERTIES AND MANAGEMENT 



The application of a soil mulch is not confined to 

 intertilled crops such as maize, potatoes, vineyards, 

 fallow, and the like. Under some conditions it may be 

 applied to grain fields with good results. In those sections 

 of the country where dry farming is practiced, it is not 

 uncommon to drag the grainfield with a sharp-tooth 

 harrow, the teeth pointing backward. This is begun when 

 the plants are small, and may be continued until they 

 attain a considerable size or until they sufficiently shade 

 the ground to greatly reduce surface evaporation. 



199. General usefulness of a mulch. While a soil 

 mulch is used primarily in order to conserve moisture, 

 its relationships are different in different regions accord- 

 ing to climatic and cropping peculiarities. In dry- 

 farming regions a mulch is maintained as nearly as possible 

 the year round, since moisture must be carried from the 

 previous summer and winter to the growing season in 

 order to supplement the rainfall occurring at that time. 

 In irrigated regions a mulch is useful in two ways by 

 conserving the rainfall and by checking the loss of irriga- 

 tion water; after the latter is once in the soil less addi- 

 tional water need be applied and the consequent cost of 

 irrigation is much less. Again, in arid regions where 

 there is an excess of soluble salts, rapid evaporation is 

 detrimental since these salts tend to concentrate near 

 the surface and become harmful to plants. The pre- 

 vention of the rise of alkali is therefore a very important 

 function of the soil mulch in such regions. 



In humid regions the utilization of a soil mulch is 

 much less intense, since the conservation of moisture 

 over long periods is unnecessary, due to the rainfall. 

 However, during the growing season periods of drought 

 occur, when if available water is lacking in the soil, the 



