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



901 



ber of bacteria and nitrogen-fixing powers of the soil, while perceptible, is 

 not as regular. The application of manure produced no difference in the 

 temperature of the soil. The temperature of the manured and unmanured 

 soils averaged very nearly the same throughout the experiment. The 

 temperature of the pots receiving the least quantities of water averaged 

 1 degree centigrade higher than the soils receiving the greatest quantity 

 of water. 



The relationship existing in the various bacterial activities of the soil 

 is brought out best by taking the average of each set of pots receiving 

 the same quantity of manure and water. Then, if the bacterial activities 

 of the pots receiving no manure and that of the pots receiving 12.5 per 

 cent of water each be taken as 100 per cent and the others on a similar 

 basis, we obtain a direct comparative value for each treatment. The 

 results so obtained are given in Table III. 



Table III. — Bacterial activities of the soil in the presence of varying quantities of manure 



and water — pot experiments 



Treatment. 



No manure 



5 tons of manure 



10 tons of manure. . . . 

 15 tons of manure. . . . 

 20 tons of manure. . . . 

 25 tons of manure. . . . 



12.5 per cent of water 

 15 per cent of water. . 

 17.5 per cent of water 

 20 per cent of water. . 

 22.5 per cent of water 



Bacteria. 



Per cent. 

 IOO 



99 

 III 

 IOO 



116 

 117 



IOO 



90 



9 1 

 79 



87 



Ammonia. 



Per cent. 

 IOO 

 122 

 I4O 



l6o 



ISO 



IOO 



III 



113 

 123 

 119 



Nitric ni- 

 trogen. 



Per cent. 

 IOO 

 I, 211 



1, 762 



2, 240 

 2,405 

 2,540 



IOO 

 Il8 

 121 

 121 



I2 3 



Nitrogen 

 fixed. 



Per cent. 



IOO 



103 



no 



105 

 103 



101 

 IOO 



108 



102 



104 

 108 



It will be observed that the manure increases the number of bacteria 

 developing upon the synthetic media, while the water depresses the 

 number developing. In neither case is the regularity as great as could 

 be desired. The ammonifying powers of the soil very regularly increases 

 as the manure applied increases. The increase becomes less each time 

 in a definite quantity as the manure increases. The water causes an 

 increase in the ammonifying powers of the soil up until 20 per cent of 

 water is applied; above this it causes a decrease. It would have been 

 very interesting and practical to have added greater quantities of water 

 to find whether it would have continued to depress the ammonification. 



The quantity of nitric nitrogen systematically increases as the water 

 and manure applied increase, and it may be seen, as would be expected, 

 that there is a close correlation between the ammonification and nitrifi- 

 cation. The nitrogen-fixing powers regularly increase up to 10 tons of 

 manure per acre; above this they gradually decrease. The water tends 



