40 Journal of Agricultural Research voi. x\i, no. 2 



nium sulphate, and also the numbers of aerobic, anaerobic, and carbon- 

 dioxid surviving microorganisms present in the soils. 



(3) All the untreated soils were quite acid and contained nitrates 

 when sampled, showing that nitrification takes place in acid soils. 



(4) The amounts of nitrates present and the nitrifying power of the 

 untreated acid soils varied with the organic matter and total nitrogen 

 rather than with the soil acidity. 



(5) Calcium-carbonate additions markedly increased the nitrification 

 of all five soils. 



(6) Fertilization tended to increase nitrification, but not so much as 

 calcium carbonate did. 



(7) Regardless of treatments the presence of growing clover kept 

 down nitrate contents of the soils. 



(8) The degree of saturation of the soils affected the nitrates present. 

 As a rule, more nitrate were fotmd in soil kept one-half saturated with 

 water than in soil kept one-fourth saturated. 



(9) The soils that had been kept fully saturated with water for the i o 

 months contained no nitrates and formed no nitrates when incubated 

 with ammonium sulphate. 



(10) The relation of nitrates present in the uncropped soils before 

 incubation to the* nitrates present after incubation shows that the ni- 

 trate contents of these acid soils tend to reach an equilibrium, above 

 which no increase is obtained without additional treatment. 



(11) The bacterial flora of each soil was different from that of every 

 other soil. 



(12) No bacteria developed into colonies visible to the eye as long as 

 plates were incubated in an atmosphere of flowing carbon-dioxid gas. 



(13) Calcium-carbonate additions increased the bacterial contents of 

 the soils. This increase was largely in the aerobic organisms. 



(14) Small increases in bacterial content resulted from the use of 

 fertilizer. 



(15) The degree of saturation at which the soil was kept changed the 

 proportions between the aerobic, anaerobic, and carbon-dioxid-surviving 

 bacteria. 



(16) Cultures from samples that had been kept one-fourth saturated 

 with water contained the largest proportions of organisms forming 

 moldlike colonies. 



(17) Under optimum moisture conditions both without and with lime 

 and fertilizer treatments the nitrates after incubation varied directly 

 with the aerobic counts. 



(18) In general, the greater the aerobic bacterial content and the 

 nitrifying power of the soil the larger the crop yields. 



(19) These investigations show many reasons why a system of soil 

 improvement which includes the addition of lime, phosphate, and or- 

 ganic matter is worth while. 



(20) It is evident that soil fertility investigations should include both 

 chemical and biological examinations of the soil. 



