20 BACTERIA AND SOIL FERTILITY 



der this condition and with these plants nitrogen no longer re- 

 mains the limiting element of crop production. For these micro- 

 scopic organisms which live within small nodules upon the alfalfa 

 are master chemists. Within their tiny laboi'atory they can bring 

 about changes which man can imitate only imperfectly with cost- 

 ly machinery and under the action of powerful electric currents. 

 In some of the experiments carried on at the Illinois Experi- 

 mental Station these minute organisms were found to increase the 

 value of the first cutting of alfalfa hay $27.80 an acre, if the 

 nitrogen in the alfalfa be counted only at the same price we 

 would have to pay on the market for an equivalent quantity of 

 nitrogen in the form of a commercial fertilizer! If these crops 

 be plowed under the fertility of the soil would be increased to 

 just that extent. One writer has said of them: "They not only 

 work for nothing and board themselves, but they pay for the 

 privilege." This is strictly true, for all they require is a plant 

 on which to grow and a well-aerated moist soil containing lime- 

 stone. Their activity is retarded in an acid soil. 



There is another class of nitrogen-gathering organisms within 

 the soil which differ from the above in that they live free in the 

 soil and gather nitrogen. Under ideal conditions they may gather 

 appreciable quantities. 



It is quite possible that much of the benefit derived from the 

 summer fallowing of land is due to the growth within the soil 

 of this class of organisms which store up nitrogen for future 

 generations of plants. It has been discovered that they are more 

 active and found in greater numbers in such soil. All of the work 

 which the farmer puts upon the soil in rendering it more porous 

 reacts beneficially upon these bacteria because they not only love 

 atmospheric nitrogen and oxygen but they must have them. 



Bacteria are found by the thousands in every drop of water in 

 the cesspool and they lie in wait and quickly devour the mate- 

 rial which enters. Paper, bone, and wood are quickly changed 

 into gases and ash. The repulsive poisonous substances soon dis- 

 appear under their magic wand, and it is only a short time until 

 the water again becomes pure. 



