102 SOIL W'ATER AND. JJS RELATION TO SOIL FERTILITY 



How Water-holding Capacity May Be Increased. Since the 

 amount of water retained against gravity by most soils is deter- 

 mined largely by texture, organic matter and structure, it is plainly 

 seen that the water-holding capacity of a sand, for example, cannot 

 be increased by improving its texture. Texture of a sand, or of 

 any soil, remains practically the same, and the structure of a sand 

 cannot be materially changed in a short time. Thus the only 

 course open, in case of sand, is to increase the organic matter. 



In case of a "heavier" soil, water-holding capacity may be 

 improved by increasing the organic matter and by loosening it if 

 it is very compact. The addition of organic matter also tends to 

 develop a crummy structure which is favorable to water-holding. 



Organic matter may be increased by plowing under clover or 

 green rye, by plowing under a good sod as often as possible, through 

 the application of farm manure and through the application of 

 peat, if convenient. 



Aiding Capillary Rise of Water. Good contact between the 

 soil particles favors capillary rise of water. This is an important 

 reason why a firm seed-bed is generally desirable. Not only should 

 the seed bed be firm, but there should also be good contact between 

 the seed bed and the subsoil in this respect fall plowing is advan- 

 tageous, also working the land and rolling it. 



A seed bed too loose and lacking good contact with the subsoil 

 is not a favorable environment in which to plant seeds, especially 

 if they be small like clover and alfalfa. If frequent rains do not 

 occur when such conditions exist, germination is poor and the 

 crops may be failures. 



Special attention should be given to compacting the seed bed 

 when deep plowing is done just before seeding or planting par- 

 ticularly when the soil is sandy or loamy. 



Subsoiling heavy soils to enable them to trap and store more 

 water is to be recommended in some instances, but subsoiling land 

 having sand or sandy subsoil is to be discouraged, since it is desir- 

 able to maintain compactness of a sand subsoil to favor capillary 

 rise of soil moisture, to retard loss of water through percolation, 

 and to lessen excessive leaching. 



Lessening Evaporation of Soil Moisture. Under field condi- 

 tions losses through evaporation may be decreased more or less 

 by developing a top layer of loose, dry soil. Such a protective 

 layer is called a "soil mulch" (Fig. 44). A soil mulch may be 

 developed and maintained throughout the growing period only in 



