Soil Fertility 59 



and in a certain soil in Maryland, if hundred-bushel corn crops 

 were removed from the soil, there would be a supply of nitrogen 

 for only nine years. Cropping of land without returning plant- 

 food to the soil is not good farming. 



The washing of the soil removes much plant-food. It is 

 the top soil, the part richest in humus and plant-food, that is 

 carried away. Some soils wash more readily than others; 

 those containing a large proportion of silt and fine sand wash 

 very badly. Soils in the Southern States wash readily, largely 

 because washing may occur during the entire winter as well as 

 during other seasons. Many soils in that section, also, are of a 

 texture that causes them to wash readily. Cover-cropping 

 and terracing will help to prevent this. In the Southern 

 States it is possible to have a crop growing on the soil all winter, 

 which helps to hold the soil from washing and stores fertility 

 in the plants. These plants can be cut for forage or be turned 

 under in the spring to supply humus and, if the crop is a legume, 

 nitrogen is added to the soil. 



Terracing to prevent washing is necessary on many farms. 

 To be effective, the terraces should be covered with vegetation ; 

 otherwise they may be quickly washed away. Grass is usually 

 employed as a covering. One grower in South Carolina plants 

 strawberries on his terraces and makes the crop profitable. 



Soluble foods are leached out of the soil. The loss in this 

 way is large in some soils, especially in those of a sandy nature. 

 One way to prevent loss by leaching is to grow a crop on the 

 soil to use up the food before it leaches away. Cover-crops 

 are useful for this purpose. More loss from leaching occurs 

 in warm climates than in cold, because freezing of the ground 

 prevents leaching. This, therefore, is another reason why the 

 farmers of the South should use winter cover-crops. 



Benefits of crop rotation. Experience teaches that the con- 

 tinuous growing of the same kind of crop, such as cotton, corn, 

 wheat, on the same land year after year results in the decrease 

 of the soil products. Rotation of crops should be practiced. 



