Introduction to the Principles of Soil Fertility 1767 



mation about the availability of the large amounts of plant-food already 

 present in the soil. Trials of fertilizers on growing crops in the field are 

 the most reliable guide. 



CONCLUSION 



It may be evident from this brief discussion, how complicated is the 

 soil in which plants grow, as well as the processes, natural and artificial, 

 by which it is rendered productive. It is the part of the farmer to direct 

 those processes by his various treatments, such as drainage, irrigation, 

 the use of lime, organic matter, and fertilizer, and the practice of tillage, 

 manuring, and crop rotation. He must consider not merely the thin 



Fig. 9. — Soil in good tilth. Fine and granular, and in proper condition to have 

 a good relation to moisture and ventilation 



surface layer turned by his plow, but also the subsoil to a depth of at 

 least three feet, which may be as capable of holding water and feeding 

 plants as the topsoil when it is put in proper condition. Neglect of the 

 subsoil is frequently the cause of poor crops. 



The soil, and the subsoil to a depth of two, three, or even five and six 

 feet, should be in condition to permit the growth of crop roots. When 

 that is possible there will be much less complaint because of the lack of 

 rainfall and the exhaustion of plant-food. That such use is possible is 

 frequently shown on individual farms in many parts of the State, and 

 especially by the use made by plants of the deep subsoil in arid and semi- 

 arid regions under small rainfall but where wise irrigation is practiced. 

 Deeper farming is one of the great needs for better soil management. 

 This means much more than deeper plowing, helpful as that will prove. 

 The depth of soil that can be turned by the plow is greatly limited. Deeper 

 farming means the better use of the subsoil, which is to be accom- 

 plished by good underdrainage and by the use of deep-rooted crops in 



