EXERCISE 51 



Fig. 65. Taking soil from an alfalfa field with which 



to inoculate soil upon which alfalfa has not been 



grown successfully 



INOCULATION OF SOILS FOR LEGUMES 



Statement; Attached"!*) the rcots of growing legumes are many nodules, or tubercles, which were 

 caused by bacteria. These bacteria penetrate the roots of the plant and draw part of their sustenance 



from the legumes and part from the air. They have the 

 power to use free, or pure, nitrogen from the air and change 

 its form so that the legume can use it. The legume in turn 

 absorbs the substance of the nodules and is nourished 

 thereby. In this indirect way legumes are able to use free 

 nitrogen. 



Object. To ascertain whether the presence of bacteria 

 is necessary for the best growth of legumes. 



Materials. Roots of as many legumes as can be ob- 

 tained; soils from an alfalfa or red or sweet clover field 

 where bacteria are present ; alfalfa seed ; clean fine sand ; 

 a one-gallon or two-gallon pail; flowerpots or tin cans; 

 formalin ; distilled rain water. 



Directions. Fill the two flowerpots or tin cans with clean 

 fine sand. Heat the sand for half an hour at a temperature 

 which will destroy all life. Place 10 cubic centimeters of 

 formalin in 50 

 cubic centime- 

 ters of distilled water and place alfalfa or red clover seeds 



in the solution for five minutes. Remove and wash with 



distilled water and plant the seeds in the two pots of soil 



previously heated. 



Water one pot with distilled water and the other with 



water prepared by filtering distilled or rain water through a 



pail half full of soil from an alfalfa or clover field contain- 

 ing plants upon which root tubercles have developed. Stir 



the soil and water thoroughly and after the soil has settled 



pour off the clear water and use it. Use fresh soil each 



time that water is to be prepared. Let the plants grow 



until a difference is apparent in their growth. Remove the 



plants and examine their root systems. 



Questions. What do bacteria supply to the plants? 



From whence is it obtained? Suppose the clover crop is 



removed from the field and only the roots left, has much 



fertility been added to the soil ? Do you think that clovers 



in the rotation will solve the soil-fertility problem if the 



crops are largely removed and only the roots and stubble 



are returned? 



References. Waters, H. J. Essentials of Agriculture, pp. 

 78-79, 205-206. Ginn and Company. Burkett, C. W. Soils, pp. 

 143-152. Orange Judd Company. Hopkins C. G. Soil Fertility ^ fi6 Tuberdes or nodules on ^ roots o{ the 

 and Permanent Agriculture, pp. 210-214. Ginn and Company. cowpea 



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