192 SOILS 



Under-draining to Deepen Shallow Soils. There 

 is another class of soils those that are shallow that 

 are improved by being drained, but these are not 

 too wet except for short periods. First, there are 

 the soils that have a hardpan close to the surface, 

 perhaps within one to three feet. This hardpan 

 may be a stratum of rock, but more often it is a 

 layer of stiff and impervious clay. The rock hard- 

 pan cannot be improved, but the clay hardpan 

 can. Water cannot readily penetrate it. It is 

 like the bottom of a shallow pan; when a heavy 

 rain comes, the pan soon fills and overflows, making 

 surface water. This can escape by surface drainage 

 or by evaporation. But such a soil quickly 

 dries out and suffers in a drought, because it 

 has so little depth. What is needed is to deepen 

 the soil to lower the bottom of the pan so that 

 it will hold more water. 



There are two important ways of deepening a 

 shallow soil. If the hardpan is close to the surface, 

 stirring the surface with a subsoil plow helps, since 

 it loosens the soil deeper than the plow, thus en- 

 abling it to hold more water. But the loosened 

 soil becomes compacted again in a few years; at 

 best the results of subsoiling are only temporary. 

 Under-drainage is permanent subsoiling; it takes 

 away the water that has cemented the subsoil, and 

 permits the air to enter it, thus promoting all the 

 fining, loosening and mellowing influences of 

 weathering. The value of under-drainage for deep- 

 ening a soil is witnessed on thousands of Eastern 

 farms. 



Draining to Improve Texture. Still another 

 type of soils those poor in texture is often greatly 

 benefited by being drained. These are mostly 

 the clayey soils that get hard, lumpy, and 



