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



917 



The irrigation water exerts a great influence upon the nitrifying powers 

 of the soil and this follows almost exactly the order followed by the 

 ammonifying series. It is greatest when a medium amount of water is 

 applied, but becomes injurious as greater quantities of water are applied 

 to the soil, especially with large quantities of organic matter. One could 

 not conclude from these results that the quantities of water here applied 

 in the presence of organic manure favor denitrification, but it is certain 

 that the conditions thus produced are not the best for the nitrate and 

 ammonia-forming organisms, and it is quite likely due to the anerobic 

 condition produced by the excess of water. It is interesting to note that 

 larger quantities of water are required on a cropped soil to exert this 

 depressing influence than on a fallow soil. The results for this series are 

 given graphically in figure 8. 



Taking the average quantity of nitric nitrogen produced in the un- 

 manured soil as 100 per cent, the soil receiving 5 tons of manure then 

 becomes 453 per cent, while the percentage produced in the soils receiving 

 15 tons per acre becomes 2,079. Thus, an enormous increase is due 

 directly to the application of manure to the soil. 



Taking the average quantity of nitric nitrogen produced in the soil 

 receiving no irrigation water as 100 per cent, the irrigated soils produced 

 with 5 inches of water, 126 per cent; with 10 inches of water, 99 per cent; 

 20 inches of water, 104 per cent; 30 inches of water, 108 per cent; and 40 

 inches of water, 89 per cent — an unmistakable reduction in the nitrifying 

 powers of soils receiving 40 inches of irrigation water. 



RELATIONSHIP IN BACTERIAL ACTIVITIES IN POTTED, CROPPED, AND 



UNCROPPED SOIL 



If we use in every case the quantity of ammonia and nitric nitrogen 

 produced and the total number of bacteria developing from the un- 

 manured in the one case and the unirrigated in the other as 100 per cent, 

 we have a direct comparison between the bacterial activities of the 

 variously treated soils. The results so obtained are given in Table X. 



Table X. — Comparison of the bacterial activities in the potted, fallow, and cropped soils 



"12.5 per cent applied. 

 *> 15 per cent applied. 



c 17.5 per cent applied. 

 d 20 per cent'applied. 



« 22.5 per cent applied. 



