Jan. 13, 1919 Nitrates, Nitrification, and Bacteria of Acid Soils 35 



tents so that the bacterial index was decreased. With the brown silt 

 loam containing considerable undecayed organic matter the acid phos- 

 phate increased both the aerobic and anaerobic counts somewhat. 

 Plate 2 shows representative petri plates from each treatment for the 

 two soils. This plate shows a marked similarity between the colonies 

 on the aerobic plates from the limed pots of both soils. The similarity 

 of the appearances of the plates from the limed and the phosphated 

 pots of tl^e whitish silt loam, the similarity of all aerobic plates from 

 the brown silt loam and the uniformity of colonies developing from the 

 brown silt loam under anaerobic conditions are to be noted. 



The black peaty sand containing six times as much nitrogen as the 

 yellow silty clay, received the same lime and fertilizer treatments as the 

 yellow clay, but gives entirely different results. Ume and fertilizer 

 both alone and in combination give increased bacterial indexes. While 

 the aerobic organisms are increased by lime, the organic matter of the 

 black peaty sand must be in an advanced stage of decay since the counts 

 are lower than they should be if the organic matter was good food for 

 bacteria. Plate 3 shows representative culture plates from this soil. 

 These illustrations emphasize the effect of lime on bacterial numbers 

 and the small proportion of the bacteria which are anaerobic. 



The dark-brown peat shows an increase of over 100,000,000 in bacterial 

 index as the result of liming. Peats in situ are generally low in bacterial 

 content. Working them over after drainage generally causes enormous 

 increases in their bacterial content. This peat, even when aerated, had 

 only iK times as many aerobic as anaerobic bacteria, but adequate 

 liming increased the aerobes more than 60 times and the anaerobes 

 over II times. The increase in anaerobes is believed to be associated 

 with the large amount of organic matter present in the soil. Plate 4 

 shows representative petri plates of the colonies developing in air and 

 hydrogen. Attention is called to the small variation in colony types 

 on the anaerobic plates as compared to the aerobic. The aerobic culture 

 plates from the heavily limed soil showed many chromogenic differences 

 between colonies not observable in the photographs. 



SOIL MOISTURE IN RELATION TO BACTERIAL COUNTS 



In addition to the incubations in air and hydrogen another set of 

 plates was incubated in an atmosphere of flowing carbon-dioxid gas 

 for 10 days. No colonies developed on this set of plates while they were 

 in carbon-dioxid gas. The counts given were computed from colonies 

 developing in 10 days in air after the plates had been removed from the 

 carbon dioxid.^ Table IV gives the counts under the different condi- 

 tions of incubation and the various soil-moisture contents. 



* These organisms, as far as tested, have been found to be spore formers. 



