374 SOIL PHYSICS AND MANAGEMENT 



3. Vegetation. Among the many plants that may be used to 

 excellent advantage in checking the deepening and widening of 

 gullies, the black locust is probably the most valuable tree. Gullied 

 soils are always low in nitrogen, yet the locust thrives in spite of 

 this fact. The roots help to hold the soil and the leaves and twigs 

 also offer some protection. The locust adds some nitrogen, to the 

 soil and grasses soon get a footing, which then catches the finer 

 material. The gully may be almost entirely filled in this way. 

 Locust trees are valuable for posts if not attacked by borers. Wil- 

 lows and cottonwoods and a few other trees may be used in the 

 same way, but their wood is of less value and few, if any, of them 

 possess the advantages of the locust. (See Fig. 181, page 368.) 



Timothy, blue-grass, redtop, sweet clover, Japan and other 

 clovers are very useful in all gullies, but more especially in wide, 

 flat-bottomed ones where erosion is not so severe as to prevent 

 them from getting a good start. 



In many localities the sod of blue-grass or tim&thy in draws is not 

 disturbed when the field is plowed for corn. Where limestone is 

 applied or where its roots can reach carbonates in the subsoil sweet 

 clover is exceptionally valuable because of its strong, rapid growth. 

 On the steep limestone slopes of Kentucky sweet clover has reclaimed 

 large areas of abandoned land which now produce excellent pasture 

 and large crops of seed. 



4. Filling with Soil. On more gently sloping land gullies 

 may be filled with soil by means of plows and scrapers. This 

 method can 'be employed with profit only on those areas where 

 more or less intensive agriculture is to be practiced or where filling 

 a few small gullies in this way will reclaim considerable areas. 

 Much subsoil will be on the surface which will be very unproductive. 

 Legumes must be grown for supplying organic matter and nitrogen, 

 thus restoring fertility. If the soil is acid cowpeas is the best crop 

 to grow. If the soil contains limestone. or if limestone is applied 

 sweet clover is one of the best legumes for the soil, as it grows under 

 very adverse conditions. Whichever crop is grown should be re- 

 turned to the soil. Figure 175, page 362, shows sweet clover grown 

 under the above conditions. 



QUESTIONS 



1. How much land has been abandoned in the United States T 



2. What percentage in Illinois is hilly? 



3. How do other states compare with Illinois in this respect? 



4. Upon what does run-off depend ? 



