60 DRY-FARMING 



decayed vegetable matter and modified by plowing, 

 harrowing, and other cultural operations. The sub- 

 soil has been profoundly modified by the action of 

 the heavy rainfall, which, in soaking through the 

 soil, has carried with it the finest soil grains, espe- 

 cially the clay, into the lower soil layers. 



In time, the subsoil has become more distinctly 

 clayey than the topsoil. Lime and other soil ingre- 

 dients have likewise been carried down by the rains 

 and deposited at different depths in the soil or wholly 

 washed away. Ultimately, this results in the re- 

 moval from the t(_)psoil of the necessary jslant-foods 

 and the accumulation in the sul)S(jil (jf the fine clay 

 particles which so compact the subsoil as to make 

 it difficult for roots and even air to penetrate it. 

 The normal process (_)f weathering or soil disinte- 

 gration wiU then go on most actively in the topsoil, 

 and the sul.)soil will remain unweathered and raw. 

 This accounts for the well-known fact that in humid 

 C(juntries any subsoil that may have l)een plowed up 

 is reduced to a normal state of fertility and crop 

 production only after several years of ex]3osure to 

 the elements. The humid farmer, knowing this, is 

 usually very careful n(jt to let his plow enter the sub- 

 soil to any great depth. 



In the arid regions or wherever a deficient rain- 

 fall prevails, these conditions are entirely reversed. 

 The light rainfall seldom completely fills the soil 

 pores to any considerable depth, lint it rather moves 



