SOIL ORGANISMS 



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formerly practiced is aii application of this principle. The soil rich 

 in organic matter was stirred and moistened to develop a large 

 amount of nitrates, which were then leached out and used for com- 

 mercial purposes, principally in the manufacture of gunpowder. 



Effect of Different Amounts of Lime Upon the Number of Bacteria per Gram 



of Dry Soil 4 



This table shows the effect of lime carbonate upon the number 

 of bacteria and indicates a much greater development for the higher 

 lime content. An excess of lime is not injurious, as in the case 

 of some other alkaline carbonates as shown in the next table. 



Effect of Alkaline Carbonate Upon Amount of Nitrates Produced * 

 1,(XK) Grams of Acid Soil 



Treatment 



Nitrates formed 



(f) Physical Composition. Certain physical phenomena upon 

 which bacteria depend for their greatest activity and development 

 take place better in the medium-grained soils than in very fine ones. 

 Very sandy soils are well aerated, but usually do not contain suf- 

 ficient moisture and food. Granulation overcomes this in the 

 heavier soils to some extent. Kven with this aid aeration and the 

 moisture conditions are not so favorable and nitrification is usually 

 slower. Tillage is more essential for these soils. Where limestone 

 is absent heavy soils may be unfavorable for bacterial activity. 

 Limestone aids in granulation and thus indirectly in aeration. 



(g) Light. Direct sunlight greatly weakens or even kills bac- 

 teria. The /one of greatest numbers is sufficiently deep so that 



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