sept. 4, 1916 Influence of Barnyard Manure on Soil Bacteria 



899 



acre. There is nothing in the results which would indicate denitrification 

 in the presence of the largest quantities of organic matter applied in this 

 experiment. The nitrifying powers of the soil increase with the water 

 applied up to 17.5 per cent. Above this it has a slight depressing effect 

 upon nitrification, probably caused by the production of an anerobic con- 

 dition, but even with the highest percentage of water and 25 tons per acre 

 of manure there is nothing in the results obtained which would indicate 

 that denitrification had taken place. These results are brought out 

 clearly in figure 2, in which is indicated on the horizontal line the per- 



pes? c&vr or Mo/srutt ^dd£V 



Fig. i. — Curves of the ammonifying powers of soil in pots with varying quantities 01 manure and water. 



centage of water and on the perpendicular line the milligrams of nitric 

 nitrogen produced in 100 gm. of soil. 



If we take the average of the nitric nitrogen produced in the unma- 

 nured pots as 100, then that of the manured pots becomes with 5 tons 

 of manure, 1,211 per cent; with 10 tons, 1,762 per cent; 15 tons, 2,240 

 per cent; 20 tons, 2,405 per cent; and 25 tons, 2,540 per cent. The 

 greatest increase per unit of manure is produced when 5 tons of manure 

 are applied. The water applied also produces a gradual increase, but 

 here likewise the greatest increase per unit of water applied is greatest 

 for the lowest application of water. 



The nitrogen-fixing powers of all the soils are fairly high, but the 

 influence of the water and manure is not as pronounced as it is upon the 



