SOIL EROSION 363 



desirable in some places, especially the vetch, as it lives through 

 the winter and begins growth early in the spring. With fall sown 

 cereals sweet clover may be used to good advantage when the soil 

 is well supplied with plant food. Wheat, rye and winter oats cover 

 the ground well and the roots are a very effective soil binder. Vetch 

 and Japan clover are probably most desirable when sufficient growth 

 is made, because of their ability to gather nitrogen, the increase of 

 which is most essential in the improvement of these soils. Crab 

 grass is a natural cover in seasons of normal rainfall, as it makes 

 sufficient growth to serve well as a surface protection, especially in 

 corn and old wheat fields. 



3. Residues. Stalks of corn or cotton may be harrowed or 

 rolled down after the crop is harvested. Tn this way they help to 

 protect the soil from the beating of rain drops and reduce some- 

 what the amount of thawing in winter and early spring. When the 

 surface soil is thawed for an inch or two, it is easily eroded. 



It is desirable, also, to cover badly eroded areas, or areas where 

 erosion is especially rapid, with straw of grain or clover, manure, 

 or other coarse material. These areas are unusually low in organic 

 matter, as more or less of the surface soil has been removed. The 

 coarse organic matter will not only hold the soil in place, but supply 

 plant food to succeeding crops. 



4. Increasing the Organic Matter. Most lands subject to 

 serious erosion have been timbered and are naturally low in organic 

 matter and nitrogen. .The hilly timber lands of Illinois contain 

 an average of 1.5 pop cent or 15 tons of organic matter in the sur- 

 face soil (two million pounds per acre). The yellow silt loam hilly 

 timber land of llardin County, 4 Illinois, which represents the 

 unglaciafed loess-covered section of the states adjoining the lower 

 Ohio and the middle section of the Mississippi river, contains as an 

 average of 15 analyses 1.1 per cent or 1 1 tons of organic matter in 

 the surface soil. The hill soils of the Piedmont Plateau. Appa- 

 lachian Mountain Plateau, and Limestone Vallevs and Upland 

 Provinces contain from one-half to two and one-half per cent of 

 organic matter/' The average organic-matter content is about 1.1 

 per cent/' Profitable crops cannot be produced without adding 

 considerable organic matter or nitrogen. 



Besides furnishing nitrogen, organic inafter aids granulation 

 and cements the finer particles together into compound granules, 

 as discussed under organic matter. These soils need the addition of 

 large quantities of organic matter to enable the surface to absorb 



