154 INFLUENCE OF MANURE ON THE SOIL 



reactions, the nitrates being built up into complex proteins. For 

 Gerlach and Vogel have shown that there are several varieties of 

 bacteria in the soil which have the power of converting ammonia, 

 nitrites, and nitrates into insoluble proteins. 



It is evident from the literature cited that there is a wide variation 

 in the ideas held concerning the influence of manure upon the 

 bacterial flora of the soil. This is due to a number of factors, chief 

 among which are: (1) variation in the physical and chemical com- 

 position of the soil; (2) a great variation in the composition of the 

 manure used; and (3) the manure added may have influenced either 

 beneficially or injuriously the water content of the soil. The results 

 noted may have been due to the moisture factor and not to the 

 manure. An experiment was conducted at the Utah Experiment 

 Station both in pots and under field conditions. Each ton of the 

 manure added was partly rotted and contained in one ton 734 pounds 

 of dry matter, 3.04 pounds of phosphorus, 13.7 pounds of potassium, 

 and 16.08 pounds of nitrogen. 



The conclusions reached follow: A calcareous soil kept in pots 

 with varying amounts of manure and different percentages of moist- 

 ure gave on bacteriological analysis at the end of four months the 

 following results : The temperatures of the manured and unmanured 

 were practically the same for the period, but the temperature of the 

 soil with 12.5 per cent, of water was 1 C. higher than soils with 

 22.5 per cent, of water. The greatest number of organisms devel- 

 oped on synthetic media from the soils receiving the greatest quan- 

 tity, 25 tons, of manure. There were more colonies developed from 

 the soil receiving 12.5 per cent, of water than from any of the other 

 soils receiving higher quantities of water. 



The nitrifying powers of the soil increased as the manure and water 

 applied increased up to 25 tons of manure and 22.5 per cent, of 

 water. 



The nitrogen-fixing powers of the soil were greatest in those pots 

 receiving manure at the rate of 10 tons an acre. Increasing the 

 water above 12.5 per cent, but not above 22.5 per cent, slightly 

 increased the nitrogen-fixing powers of the soil. Nothing in the 

 results indicated that the application of manure up to 25 tons an 

 acre and of water up to 22.5 per cent, caused denitrification in the 

 soil. 



Bacteriological analyses of fallow field soil receiving no manure, 

 5 tons, and 15 tons an acre and receiving no water, 5 inches, 10 inches, 

 20 inches, 30 inches, and 40 inches of irrigation water, indicated that 

 the maximum number of bacteria were obtained from the soil 

 receiving 15 tons of manure. The application of irrigation water 

 up to 20 inches increased the bacterial count, the increase being 

 most noticeable in the soil receiving the greatest quantity of manure. 



If the ammonifying power of the unmanured soils is considered 



