240 



Nature-Study Agriculture 



Conditions 

 thai 



encourage 

 the helpful 

 bacteria in 

 the soil 



The bad 

 effect of 

 sour soil; 

 the remedy 



supply of barnyard manure plowed or spaded into the 

 earth. The bacteria, in using this as food for them- 

 selves, convert it into food for the plants. Any mineral 

 plant-food elements, like potassium and phosphorus, that 

 are found in manure or other humus-forming materials, 

 are set free by the bacteria for the use of plants. There 

 are many bacteria in manure before it is put on the 

 land, and one of the principal reasons for using it is to 

 inoculate the soil with a new supply of bacteria. 



Moreover, as we saw in Chapter Four, some of the 

 bacteria that live in the roots of legumes and others 

 that live on refuse materials in the soil greatly benefit 

 crops by increasing the supply of nitrogen available for 

 plants. This is especially true in dry-farming regions, 

 where bacteria penetrate the soil more deeply than they 

 do in wetter regions. Moisture and air are both neces- 

 sary for the life of these beneficial bacteria. For their 

 best development, the soil should be damp enough to 

 crumble readily when turned over with the spade, but 

 it should not be so wet that it can be molded into 

 shape in the hand. If the ground is kept soaked with 

 water, the air cannot penetrate among the soil grains 

 as it should and so be available to the bacteria. Air- 

 ing the soil by frequent cultivation is one of the most 

 important means of stimulating the activity of bacteria. 

 Killing weeds is not the only purpose in hoeing a garden 

 or plowing a field. 



Sourness of the soil will kill most kinds of beneficial 

 bacteria. A stiff soil that is poorly drained is the most 

 liable to become sour, and the best remedy for sourness, 

 aside from improving the drainage, is to treat the soil 



