THK I'KR'nLlTV 01< THE SOIL 23 



denitrifying organisms than nitrifying bacteria, although the loss 

 of nitrogen from well drained and tilled soils is not large, 

 because the denitrifying bacteria cannot attack the nitrogen in 

 such soils. The nitrogen wasting bacteria work considerable 

 damage in manure heaps. 



Organisms that Gather Nitrogen. — Other organisms found in the 

 soil that exert an effect on its fertility are those that live in 

 the tubercles or nodules on the roots of certain plants called 

 the legumes, of which cowpea, bean, pea, clovers, alfalfa, vetch, 

 etc., are examples. These plants through the action of these 

 bacteria, have the power of accjuiring the free gaseous nitrogen 

 from the air and utilizing it in their growth. The bacteria se- 

 cure this free nitrogen from the air in the soil and the plant 

 acquires it from the bacteria. When the plant dies the nitrogen 

 left in the roots remains in the soil and thus enriches it. The 

 particular bacterium can only attach itself to the legume it is 

 suitable to. That is, bacteria forming tubercles on the roots of 

 clover will not grow on cowpea roots. When there is a plenti- 

 ful supply of nitrogen as nitrates in the soil the legumes will 

 not always form tubercles and utilize the free atmospheric ni- 

 trogen, but will gather their supply from the soil. Legumes 

 therefore are able to secure nitrogen from the soil and the air. 

 The tubercles seem to form better in alkaline soils containing 

 lime. 



Inoculation of the Soil. — The absence of tubercles on the roots 

 of legumes may therefore be due to the absence of the particu- 

 lar bacteria required, to the excess of nitrates, or to the acidity 

 of the soil. Should the soil be deficient in the particular bac- 

 teria needed, the soil should be inoculated. This inoculation is 

 accomplished by sowing soil from a neighboring field that has 

 produced a good crop of the kind desired, or if such a soil can- 

 not be obtained, by inoculating the seed before planting with a 

 pure culture which has been obtained from the tubercles of the 

 kind of crop to be raised. These cultures may be obtained from 

 the United States Department of Agriculture and dealers in seeds. 

 In using soil from another field for inoculating, fungus diseases. 

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