8 4 



THE ESSENTIALS OF AGRICULTURE 



may be appreciably decreased. The Chinese people are farm- 

 ing lands that have been cultivated for four thousand years, and 

 they are maintaining many of them in a high state of fertility ; 

 but they have found it necessary to keep up the supply of organic 

 matter, and to return to the land each year the equivalent of the 

 plant food removed. It is only in the older sections of the United 

 States that there is anything like a well-established system of 



FIG. 37. Terrace farming prevents erosion 



Where soil is not frozen during the winter and rains are frequent, the loss from erosion 



is great. In such regions erosion is often prevented by terracing. (Photograph from 



Bureau of Soils, United States Department of Agriculture) 



returning to the soil the complete equivalent of the plant food re- 

 moved. The majority of American farmers are depending largely 

 upon the virgin fertility of the soil, and are pursuing methods 

 of farming which are destructive of the store of plant food. 



93. Waste through surface washing. There is no accurate 

 way to estimate the loss of fertility through surface washing, or 

 erosion ; but the loss is great (Fig. 36). The amount of erosion 

 occurring when lands are covered by vegetation is small ; but 



