SOILS AND FERTILIZERS 385 



Plowing up and down the hill is apt to leave small depressions be- 

 tween furrows in which the water will accumulate and do washing. 

 Planting should be done across the slope. 



While the direction of plowing is important the depth is 

 equally so, since this controls in large part the amount of run-off. 

 A deep layer of loose soil \vill absorb a considerable rainfall with- 

 out run-off. Five inches of such soil will readily absorb one inch 

 of rainfall. Deep plowing mixes the organic matter with the soil 

 to considerable depth thus keeping it loose so that the water will 

 penetrate it quite rapidly. 



In the southern states it is a somewhat common practice to ter- 

 race the slopes, the kind of terraces depending upon the character 

 of the soil and subsoil. Where the soil is pervious, such as a sandy 

 soil, the terraces may be run on a level across the slope but more 

 frequently they are given sufficient fall so that the water runs along 

 the terrace without doing much washing. The water is kept on the 

 terrace by an embankment on the lower edge. Hillside ditches are 

 sometimes used to prevent washing. A ditch is run across the slope 

 with a fall sufficient to carry the water off without doing any damage. 

 A number of these are made upon the slope, each one carrying off 

 its share of surplus water. The distance between the ditches is 

 determined by the slope, the steeper the slope the closer the ditches. 

 Sometimes the hillside ditch and terrace are combined, the ditch 

 being placed at the edge of the terrace. 



The owner of very rolling or hilly land must be on the lookout 

 constantly for incipient gullies and must use every means for pre- 

 venting their enlargement. The fact that slopes are not uniform 

 allows the water to accumulate in draws, thus increasing its 

 volume and velocity and multiplying its washing power many times. 

 Unless some means are taken to prevent it, the water soon grinds 

 out a formidable gully. 



It is a somewhat common practice to scatter straw in these 

 draws in the fall or to build straw dams across them at frequent 

 intervals. These serve to check the velocity of the water and catch 

 the sediment, but frequently the run-off is so great that the straw is 

 carried down the draw and lodges at the base. 



Control of Blowing Soils. Some soils blow very easily and are 

 damaged by light winds. Ordinarily, however, the soil has a fair 

 power of resistance, and it is only from heavy winds that serious 

 damage may be expected. The velocity of the wind is not the only 

 factor which affects the problem. Its direction and constancy, as 

 well as the moisture content of the air and soil are also of impor- 

 tance. Sandy soils are especially liable to damage by blowing, not 

 only because of their low natural cohesion, but because they are 

 usually well drained. The danger of blowing must always be borne 

 in mind in reckoning the value of sandy lands. 



A clay soil is less subject to blowing, not so much because clay 

 particles hang together better than those of sand, though this is of 

 some importance, as because the w r ater-holding power of clay is bet- 

 ter, and it is therefore more likely to be able to keep itself moist. It 



