WIND BREAKS AND SHELTER BELTS 91 



be emulated. Small grains, such as winter wheat and winter rye 

 for the north, and winter oats for the south, serve well the pur- 

 pose of a winter cover. These small grains may have mixed with 

 them for this purpose such legumes as may be suited to the sec- 

 tion where they are used. Crimson clover and winter vetch do 

 well in the middle and southern states. Seed for such winter cover 

 crops may be mixed and sown between the rows of corn, cotton, 

 tobacco, sugar cane and other cultivated crops. As soon as the 

 main crop is harvested the growth of the cover crop becomes more 

 vigorous and a fine cover for winter conditions is produced. 



Besides these benefits of cover crops there are several other 

 uses discussed in Chapter IX. 



Adding Humus. The presence of humus in all kinds of soils 

 improves them in a number of ways. We have already seen that 

 humus increases the water-holding capacity of both clay and sandy 

 soil. Soils containing a large proportion of humus will receive 

 the rain water more readily than those containing little humus. 

 If the rain falls rapidly this characteristic of soils is very impor- 

 tant. Much surface run-off is thereby prevented. 



As soils containing little humus will absorb much less water, 

 they soon become saturated by continuous rains. If other rains 

 follow upon this condition the soil is either washed away in masses 

 or rivulets will be formed, cutting gullies down the hillsides, and 

 torrents of water may rush to the valleys, bearing with them much 

 valuable plant food and soil materials. The addition of humus to 

 the soil tends to prevent all of this, as much more water will be 

 held by the soil and washing will not take place until the soil be- 

 comes saturated. Methods of adding humus have been mentioned 

 in Chapter VII. 



Wind Breaks and Shelter Belts. In all climates wind causes 

 much loss of soil moisture. Water which is once taken into the 

 soil should not be allowed to escape by evaporation from the sur- 

 face, if it can be prevented. One method of reducing surface 

 evaporation is by using wind breaks or more extensive shelter 

 belts. In a level region the influence of such a barrier will be ef- 

 fective for a distance of ten or twelve times the height of the wind 

 break. Within this area the evaporation of water will be greatly 

 reduced because of protection from rapidly moving air. Crops in 

 this area will suffer less from drought because of such protection. 



A number of crops will thrive better when they are not dis- 

 turbed by wind, arid the presence of an abundance of soil mois- 



