sept. 4, 1916 Influence of Barnyard Manure on Soil Bacteria 919 



The results for manure show a remarkable uniformity throughout. 

 With one exception it has increased the bacterial count and also the bac- 

 terial activities of the soil, and this is about the order throughout. The 

 ammonifying and bacterial counts are increased more by the manure in 

 the fallow than in the cropped soil. 



The irrigation water applied apparently increases the bacterial count in 

 the fallow and cropped field soil but it apparently depresses it in the potted 

 soil. The ammonifying powers of all soils are uniformly increased with 

 increasing amounts of irrigation water applied up to a certain application. 

 Above this there is a depression. Greater quantities of water must be 

 applied to cropped than uncropped soil in order to cause this depression. 

 This is mainly owing to the influence of the plant upon the moisture 

 content of the soil. 



The nitrifying powers of the potted soils are very uniform in showing 

 a beneficial effect due to the water. The cropped soil is not so uniform, 

 while the fallow soil shows a depressing influence. These apparently 

 contradictory results are quite likely caused by a difference in treatment, 

 for the water in the three different sets of soil may have been far from the 

 same. 



RELATIONSHIPS BETWEEN BACTERIAL ACTIVITIES AND CROP- 

 PRODUCING POWERS 



The results herein reported, together with those published by 

 Dr. Harris (19) upon Greenville soil, make it possible to compare directly 

 the crop produced on the soil as an average of five years with the bac- 

 terial activities of the soil. This is done in figures 9 and 10, in which 

 the bacterial activities and crop-producing powers of the unmanured 

 soil are taken as 100 per cent and each of the manured plots compared 

 with this. In the case of water applied the bacterial activities and 

 crop produced upon the soils receiving no irrigation water are taken as 

 100 per cent and the others compared with this. 



An examination of figure 9 shows a remarkably close correlation 

 between the crop produced and the bacterial activities of the soil. The 

 extent to which the bacterial count and ammonifying powers of the 

 soil are increased by the manure applied is almost quantitatively the 

 same as the increase in the crop produced on the manured soil. The 

 increase in the nitrifying powers of the soil is much greater than the 

 crop increase due to manure, but they are all of the same order. 



An examination of figure 10 reveals the fact that the application of 

 5 inches of irrigation water increases in nearly the same proportion 

 the crop produced and the bacterial activities of the soil. The average 

 percentage for the crop is 112, while the total average bacterial activi- 

 ties is 113 per cent. The crop produced on the soil receiving 10 inches 

 of water is slightly less than that produced on the soil receiving 5 inches 

 55S51 — 16 4 



