52 



SOIL BACTERIOLOGY 



Exercise i6 



Effect of Soil Type on Nitrification 



1. Weigh out four loo-gram portions of garden soil, 

 field soil, and acid soil into clean, dry tumblers. 



2. In one-half of the tumblers mix thoroughly with the 

 soil I per cent, of clover tissue. 



3. Arrange as follows: 



I and 2, garden soil untreated. 

 3 and 4, garden soil plus i per cent, clover. 

 5 and 6, field soil untreated. 

 7 and 8, field soil plus i per cent, clover. 

 9 and 10, acid soil untreated. 

 (/) II and 12, acid soil plus i per cent, clover. 



4. Add moisture until the soil is two-thirds saturated, 

 allow it to stand for one hour, and remix. 



5. Cover with Petri dishes and incubate at 28^ C. 



6. After three weeks determine the nitrate nitrogen 

 (see p. 143) in numbers x, 3, 5, 7, 9, and 11; after 6 weeks 

 in numbers 2, 4, 6, 8, 10, and 12. 



Table 21 — Efect of Soil Type on Nitrification 



(a) 



ib) 



W 

 id) 





So'I and treatment 



Nitrate nitrogen m loo gra of soil 





No 



After twenty-one days 



After forty-two days 



Nitrified. 





Total 



Blank 

 subtracted. 



Total 



Blank 

 subtracted 





I 



2 



Per cent. 

 Garden. 



Garden i clover. 



Mgm. 



Mgm. 



Mgm 



Mgm 



Per cent. 



3 

 4 



Field. 



Field I clover. 













5 

 6 



Acid. 



Acid I clover. 













