922 Journal of Agricultural Research vol. vi. No; as 



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

 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 at the rate of 10 tons of manure per 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 per acre and of water up to 22.5 

 per cent caused denitrification in the soil. 



Bacteriological analyses of fallow field soil receiving none, 5 tons, and 

 15 tons of manure per acre and receiving none, 5 inches, 10 inches, 20 

 inches, 30 inches, and 40 inches of irrigation water gave the following 

 results. 



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, being most noticeable in the soil receiving 

 the greatest quantity of manure. 



If the ammonifying powers of the unmanured soils are considered as 100 

 per cent and the unirrigated as 100 percent, the manured and irrigated soils 

 then become with 5 tons of manure, 147 per cent; with 15 tons of manure, 

 188 per cent; 5 inches of water, 106 percent; 10 inches of water, 117 per 

 cent; 20 inches of water, 108 percent; 30 inches of water, 106 per cent; and 

 40 inches of water, 108 per cent. Large quantities of irrigation water 

 produced the greatest depressing effect in the presence of 15 tons of manure 

 per acre. 



The application of manure to a soil increases its nitrifying powers. 

 The application of irrigation water to a fallow soil apparently depresses 

 its nitrifying powers. 



Fewer organisms develop on synthetic agar from a cropped than from 

 a fallow soil. The application of manure to a cropped soil increases the 

 bacterial count of the soil. The greatest number of organisms developed 

 from the soil receiving 10 inches of irrigation water. 



The ammonifying powers of the cropped soils were slightly lower than 

 similarly treated fallow soils. The application of 5 and 1 5 tons of manure 

 per acre to a soil increases the ammonifying ^powers of the soil. The 

 application of irrigation water up to 30 inches increases the ammonifying 

 powers of the soil. The greatest increase resulted in those soils receiving 

 15 tons per acre of manure. The application of 40 inches of irrigation 

 water to corn land, especially to that receiving 15 tons of manure per acre, 

 depresses the ammonifying powers of the soil. 



The nitrifying powers of fallow soil were higher than similarly treated 

 cropped soils. The application of manure to a cropped soil greatly 

 increases its nitrifying power. The application of irrigation water up to 

 30 inches, especially to a soil receiving 1 5 tons of manure per acre, greatly 

 increases its nitrifying powers. 



