14 



V ERTICAL FARMING 



of soil from which to draw moisture and food, and consequently 

 yields heavier crops. In another paper the good effects of this 

 open structure on beneficial bacteria will be pointed out. 



Hardpan and Plow Soil. Another soil structure that needs 

 attention is hardpan. Sometimes this is simply the tight pud- 

 dled clay that has already been described ; and sometimes it is 

 clay, silt or sand that has been cemented together by some 

 chemical or mineral substance in the soil, or by the soil particles 

 themselves being so tightly pressed together that they prevent 

 the movement of water and air, and retard the growth of roots. 

 One kind of hardpan is called plow sole, and is found just at 

 the bottom of the plowed furrow where the slide of the plow 

 has been for years packing down the soil just where it needs to 



COMMON TYPES OF HARDPAN 



be opened. The relief from such conditions is found in deep 

 cultivation that will crack the material to pieces and permit 

 good drainage where it is bad. This breaking must, of course, 

 be deep enough to reach the seat of the trouble. Any adverse 

 conditions, such as an excess of alkali or a lack of lime, should 

 be immediately corrected. 



Soils and Subsoils. By soil we mean the surface as con- 

 trasted with the lower stratum of subsoil. Ordinarily they have 

 come from the same source, and at times are so much alike that 

 it is hard to distinguish between them. This is particularly 

 true in the semi-arid regions, and in the deep aluvial belts. 

 Usually there is a difference in texture, structure, and color. 

 The soil has been well weathered and has undergone changes 



