TILLAGE 



233 



with different depths of air-dry mulches, the soil used being the 

 Leonardtown loam: 



Loss of Water by Interstitial Evaporation, and Diffusion Through Mulches of 

 Varied Thickness of Leonardtown Loam 1 



With a 1^-inch mulch of Takonia lawn soil the loss of moisture 

 amounted to one inch in six years. The amounts lost are so 

 small that they need not he taken into account. I nder field con- 

 ditions a mulch is rarely ever perfect. There will he some places 

 where capillarity is at work. Hence under Held conditions labora- 

 tory results are seldom attained, hut they furnish principles to 

 guide in farm practice. All mulches enclose air of high humidity, 

 thus retarding or preventing evaporation from the moist soil be- 

 neath. The dry layer prevents capillary movement to the surface 

 and is made much more effective by its looseness. 



There are two kinds of mulches, artificial and soil mulches. 



(a) Artificial mulches are formed by the application of 

 manure, straw, chaff, peat, leaves, sawdust and other materials 

 to prevent evaporation. This method must necessarily be very lim- 

 ited in its application because of the expense attached and labor 

 involved. Such mulches are, however, very effective. At the same 

 time other objects are accomplished, such as preventing the growth 

 of weeds and adding plant food. Strawberries and bush fruits are 

 sometimes mulched with straw, manure or leaves. "' Straw" pota- 

 toes are grown quite extensively on the deep loessial soils along the 

 Mississippi river. The potatoes are planted three or four inches 

 deep in the soil. After the soil becomes warm and before the 

 potatoes come up they are covered with straw to a depth of six or 

 eight inches. It keeps down the weeds, conserves moisture and 

 furnishes some plant food which is leached < ut of the straw into the 

 soil. 



In jMirope and other countries stones are placed upon the sur- 

 face of the soil in hillside vineyards to conserve the moisture. 

 Gravel is sometimes applied for the same purpose. 



(b) Soil mulches are by far tin 1 most practical and common 

 means of conserving moisture. They are applicable to all climates 



