SOIL EEOSIOlSr IN THE SOUTH. H 



water. The most effective methods make use of both pruiciples. 

 The porosity of the soil may be increased by the incorporation of 

 organic matter and by breaking the soil to considerable depth. Deep 

 plowing alone is not so beneficial as when used in conjuction with the 

 incorporation of organic matter in the soil. The organic matter 

 promotes a granulation of the soil particles and thus produces a soil 

 with larger spaces between the soil granules. The rate of absorption 

 is greatly increased and the storage capacity enlarged. 



Tillage operations which move the soil to considerable depth tend to 

 lessen erosion. They furnish a larger reservoir for the reception and 

 retention of water. Prehminary experiments in this laboratory 

 indicate that the dust mulch may have no advantage and is, possibly, 

 a positive disadvantage. The fine particles of dust, when sub- 

 jected to a sudden shower, are beaten into a thin layer of puddled 

 soil on the surface which prevents rapid absorption and allows water 

 to flow off the surface of the soil. 



The methods that decrease the velocity of the running water are 

 those in which impediments are placed in the path of the run-off. 

 For every given velocity of running water there is a maximum amount 

 of material that can be carried in suspension, and this amount in- 

 creases with the velocity. If, then, flowing water carrying its maxi- 

 mum load has its velocity reduced it becomes overloaded and must 

 deposit part of the load. If the velocity remains low the carrying 

 power of the water is small. With the methods intended to check 

 the velocity of the water belong the construction of various forms of 

 terraces and the growth of vegetation or the placing of any impedi- 

 ments in the path of the water. 



LAYING OFF TERRACES. 



Terraces, no matter of what kind, should be laid off level or 

 nearly so. The most common way is to use a levehng instrument 

 and a rod with target attached. In laying off the terrace, the instru- 

 ment is set on the highest part of the land and the bubble brought to the 

 middle of its tube. The rod is placed by the level and the target moved 

 to a height 3 feet above the fine of sight. The rod should then be 

 moved downhill until the target is in the line of sight. The bottom 

 of the rod will then be 3 feet below the position of the level. Other 

 points at the same level, 10 or 15 paces apart, should be located and 

 through these points the terraces constructed. After the line of one 

 terrace is located, the level may be set upon one of the points marked, 

 proceeding as before. The terrace lines will th(ui follow the contour 

 of th(! hills. If slight (ley)reHsioiis occur between two points, it is 

 best not to change ih(! tcuTiicc^ line, l)ul, to fill in the depression. 

 Instead of using u level, good resulLs luiiy Ix; ol)iiiiu(Ml with an inij)le- 



