384 MISCELLANEOUS FARM SUBJECTS 



on steep slopes and hillsides. Hills are frequently broadly dome 

 shaped with a profile such that the velocity of the water increases 

 toward the brow of the hill; due to an increase, both of slope and 

 volume of water. This gives a skirt or zone of badly-eroded soil 

 while the top of the hill or ridge has suffered comparatively little 

 from washing. The gullies thus formed work their way farther 

 up the hill by what geologists call head erosion until a point is 

 reached where the concentration of the run-off is not sufficient to 

 produce a gully. In some cases the gullies are formed by the reced- 

 ing of small waterfalls. This is especially true where grass is grow- 

 ing in a draw and the gully starts in from below. The fall gradually 

 travels up the draw, the falling water undermining the precipice 

 and causing it to fall in. Gullies formed in this way are usually 

 deep and wide and very difficult to fill. 



The amount of organic matter varies quite widely with the 

 type of soil, and it is necessary to increase the amount to an extent 

 that it will cement the small particles of the soil so they cannot 

 easily be washed away. 



The effect of organic matter on a soil is to keep it loose and in 

 condition so it will not compact readily and to bind the finer soil 

 particles into granules or crumbs, both of which tend to make the 

 soil more porous. This increase of porosity gives a greater power 

 of absorption and in this way diminishes the amount of surface run- 

 off and lessens the washing. Soils rich in organic matter do not 

 wash badly because the granular structure is developed in them, 

 and these compound particles will not be carried so readily by the 

 water as the individual particles. In soils deficient in organic mat- 

 ter, a heavy rain will so compact them that but little absorption 

 can take place. When the surface of such a soil dries it becomes very 

 hard and forms what is commonly called a "crust." With a fair 

 supply of organic matter in the soil it is not difficult to keep a 

 mulch on the surface for conserving moisture. 



The direction of plowing, planting and cultivation is usually 

 determined only by convenience and regardless, too often, of con- 

 sequences. The farmer should learn to look not only to the present, 

 but also to the future of his soils. Plowing is more frequently done 

 up and down the hill than in any other way. The making of dead 

 furrows in this direction is bad practice. Nature could not desire 

 a better beginning for a gully. The work of one season's run-off 

 may be sufficient to produce a gully that the next season's tillage 

 operations does not fill and the slight draw soon increases and be- 

 comes a source of annual trouble. The slopes should be kept as 

 uniform as possible to prevent any accumulation of water in draws. 



On land liable to serious washing plowing should always be 

 done along contour lines or across slopes. In the southern states 

 where they have studied the problems of soil washing more than 

 in any other region contour plowing is universal. From Virginia 

 to Arkansas this is the only method practiced on rolling land. 

 The water in running across the furrows meets with more obstruc- 

 tions and greater resistance than in running with the furrows. 



