352 FIELD CROPS 



time yield a valuable crop of hay or seed, it is easy to see how 

 important they are to us. 



449. Conditions Necessary for Nitrifying Bacteria. Air 

 is one of the essentials for the growth of nitrifying bacteria. 

 Unless the soil is in good condition to admit a plentiful supply 

 of air, these bacteria are unable to do their work. Tillage 

 is beneficial to them, as it stirs the soil, loosens it, and admits 

 air. Drainage is also helpful, for a soil which is full of water 

 can not admit the necessary air. Few leguminous plants 

 grow well on low, wet, sour land, though alsike clover thrives 

 in such situations. Sour or acid soils are not suitable for 

 the growth of these bacteria; this condition can be remedied 

 by the addition of lime. The acidity of the soil can easily 

 be tested by applying a little of the moist soil to litmus paper. 

 If the soil turns blue litmus paper red, it is acid and needs 

 lime for the best growth of leguminous crops. The applica- 

 tion of a half-ton or a ton of lime to the acre, or double that 

 quantity of ground limestone, will generally correct this 

 acidity. 



450. Inoculation. Though the forms of nitrifying bac- 

 teria on the roots of our various legumes are very similar, 

 they can not usually be transferred from one kind of plant 

 to another. For this reason, it is sometimes necessary in 

 introducing a legume into a new community, to supply it with 

 the proper bacteria by means of inoculation. As the bacteria 

 are very small and increase rapidly under favorable condi- 

 tions, a small quantity of them will inoculate a considerable 

 area. One of the best methods of inoculation is to take 

 several hundred pounds of soil from a field on which the crop 

 in question has been growing and scatter it on the field to 

 which it is to be introduced. This is sometimes expensive, 

 particularly if the soil has to be shipped some distance, as 

 the transportation charges will then be heavy. Five to 



