HOW A SOIL MULCH CONSERVES MOISTURE 



103 



field?? planted to crops like corn, potatoes, .cotton, or any other 

 crop planted in rows so as to permit of intertillage. 



What Constitutes a Good Soil Mulch. — On silt loams, clay 

 loams and clays a good mulch consists of a layer of loosened and 

 dry soil composed either of crumbs or a mixture of crumbs and 

 small lumps. A dust mulch is undesirable because it becomes a 

 hard crust when a hot sun shines upon it after a rain, whereas a 

 crummy layer does not crust and bake so easily. 



A good mulch on sandy soils consists of a loosened and dry layer 

 of sand 



Fig. 44. — How a soil mulch conserves moisture. The footprints are kept moist because 

 the soil moisture is permitted to move to the surface and evaporate. After awhile the foot- 

 prints will become hard and dry, while the soil beneath the mulch will be mellow and moist. 



'K 



In a humid climate it is not generally necessary to make a soil 

 mulch deeper than three inches. Many are very effective when only 

 an inch or two in depth, especially in gardens and on heavy soils. 



How a Soil Mulch Conserves Moisture. — The protective action 

 of a soil mulch in lessening the loss of moisture is based on three 

 principles: (1) The looseness of the soil hinders the movement 

 of capillary water from soil particle to soil particle. (2) The dry 

 surfaces of the soil particles and crumbs offer resistance to the up- 

 ward movement of water films. (3) A surface layer of dry soil 

 keeps the soil below it somewhat cooler, thus lessening the ten- 

 dency of the soil moisture to evaporate. When the surface layer 

 of a soil is loosened, therefore, the capillary rise of moisture is 



