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INFLUENCE OF HEAT AND POISONS ON 

 SOIL BACTERIA 



Nature repairs the flesh wounds of man with scar tissue, the 

 broken bones with new cartilage, and the injury to the oyster's 

 shell with a pearl. The reparation in each case is in excess of that 

 required. This appears to be a general law in the animal king- 

 dom. Now, injure the bacterial flora of the soil, and what will 

 happen? Do ihe remaining microbes dwindle and eke out a 

 scant existence? Or does a greater and more powerful variety 

 spring from the ruins? 



Heat.— The early Romans understood that the heating of soil 

 rendered it more productive, and this has been the experience of 

 the practical farmer down through the ages* The place where 

 a pile of weeds has been burned is perceptible from the deeper 

 green of the plant growing thereon during the succeeding year. 

 The dry-farmer in the arid regions knows that the burning of 

 heavy stubble is followed by a better crop. It is self-evident 

 that this gain cannot come from the few pounds of potassium or 

 phosphorus which is contained in the ashes, for often most of 

 these are carried from the soil by winds. 



The work of the modern chemist has shown that the heating of 

 a soil increases its soluble plant- food. Possibly some of the or- 

 ganic compounds are burned and the phosphorus and potassium 

 liberated. It may be that the heating of the nitrogen compounds 

 renders them more vulnerable to the attacks of the microbes. It 

 was thought until the dawn of the twentieth century that these 

 changes were sufficient to account for the observed effect upon 

 the crop, but the recent researches of the biologist have shown 

 that the partial sterilization of soil by heating to a temperature 

 of 60^ C. or more caused at flrst a decided decrease in the number 

 of microorganisms which it contains. This is followed by a 



