102 The Potato 



soils are lightened, often to a degree which insures 

 success instead of failure with the potato. Sandy soils 

 are improved by their particles being bound together. 

 The presence of abundant organic matter makes the soil 

 more healthy as a home for plants and for the beneficial 

 soil bacteria. Both need water and air. The plant-food 

 in the organic matter is in condition to feed the crop as 

 fast as it decays and breaks down. Indirectly the decay 

 helps to dissolve the mineral plant-food in the soil. 



Many kinds of bacteria and other microscopic forms of 

 plant life are found in the soil. Their action and value 

 are seldom understood by farmers. Too often the word 

 " bacteria " conveys only the idea of disease, or at most 

 that of the particular bacteria associated with legumes 

 to take nitrogen from the air. These latter form but a 

 fraction of the microscopic life of the soil, part of which 

 is beneficial and part detrimental. Organic matter in 

 and on the surface of soils is the food of many kinds of 

 bacteria, and is broken down by them to forms which 

 plants can assimilate. The nitrogen of organic matter 

 is changed first to ammonia and then to the soluble 

 nitrate form. Other bacteria like the azotobacter group 

 take nitrogen directly from the air without being asso- 

 ciated with any particular plants. The solution of 

 mineral plant-foods is helped by some kinds of bacteria. 

 The statement is generally true that the fertility of a soil 

 varies according to the number of bacteria present. The 

 number of the beneficial forms is increased by attention 

 to maintaining the best conditions for their growth, as a 

 large supply of organic matter for their food, an alkaline 

 soil, sufficient water but not too much, and sufficient 

 soil air. 



Organic matter in the soil is of so great importance to 



