202 THE PRINCIPLES OF SOIL MANAGEMENT 



and sawdust, are very effective as a mulch, but some 

 precautions should be observed in their application. 

 For example, the oak is rich in tannic acid, which may 

 be washed out of the mulch into the soil and cause 

 injury to its producing power, by its effect on the growing 

 plant. In some European countries, as well as in a few 

 places in America, stone has been drawn on the soil, 

 particularly in orchard and vineyard culture, to serve 

 as a mulch, and with markedly beneficial effects. Par- 

 ticularly is this true on those lands too steep to permit 

 cultivation. And, as a corollary to this practice, it has 

 been observed in the fruit-growing section of the Ozark 

 Mountains, and doubtless in other regions, that the 

 removal of stone from the land not only permits the 

 soil to become more hard, but also reduces crop yield 

 by increasing the loss of moisture. It is therefore for 

 the farmer to decide whether the inconvenience to tillage 

 or other operations due to the presence of the stone may 

 not be more than offset by their beneficial effects. A 

 layer of two or three inches of coarse sand or fine gravel 

 is a very effective mulch, and is frequently used in green- 

 house practice. 



The above-mentioned mulch materials are all strictly 

 artificial, and their application is greatly limited, due 

 to the lack of material and the expense involved. They 

 are therefore used only under special conditions. But 

 the second type of mulch is almost universal in its 

 practical availability. 



Almost any soil may be converted into an effective 

 mulch by proper treatment. This treatment will differ 

 with the character and condition of the soil and the 



