May 28, 1917 
Influence of Crop , Season , Heater on Soil Bacteria 
295 
Coleman’s (7) work with a loam soil showed nitrification to be most 
active when the soil contained 16 per cent of water. It was greatly 
retarded when the water content was reduced to 10 per cent or increased 
to 26 per cent. Not only nitrification but ammonification is dependent 
upon the moisture content of the soil. However, Lipman and Brown 
(31) found ammonification in a loam soil increased with increased water 
content even up to 35 per cent of the weight of the soil; but nitrification 
was most active in the same soil with a moisture content of 15 per cent, 
was only slightly less active with 10 per cent of moisture, and was still 
quite marked when the soil contained only 5 per cent of moisture. 
However, later Lipman, Brown, and Owen (32) found ammonification to 
increase as the water added increased up to a certain percentage, which 
varied with the physical nature of the soil; but larger quantities of water 
reduced the ammonia recovered. Moreover, the work clearly demon¬ 
strates that the optimum moisture content for maximum ammonification 
is higher than it is for maximum nitrification. 
Engberding (15) considered that the moisture content of a soil had a 
greater influence on numbers than did temperature; and the work of 
King and Doryland (30) clearly indicates that excessive soil moisture 
reduces both the number and activity of soil bacteria. 
Patterson and Scott’s (43) work is interesting in that they found 
nitrification to be inactive in sand and clay soils which still contained 
about three times as much moisture as in their average air-dry con¬ 
dition. At the lower limits of moisture less water starts nitrification in 
sand than in clay. At the higher limits of moisture less water stops 
nitrification in sand than in clay, while the optimum amount of water 
probably varies for each soil; it is higher for clay, yet for both soils it lies 
within the range of from 14 to 18 per cent. A rise above the optimum 
amount of water is more harmful than an equal fall below it. 
The work of the Utah Experiment Station (56) demonstrated that the 
application of irrigation water to a soil has a distinct beneficial effect 
upon nitrification, being greatest where 15 inches of water were applied 
when the nitric nitrogen formed amounted to 28.5 pounds per acre-foot 
of soil. The greatest benefit per inch of water, however, was obtained 
where only 7.5 inches of water were applied, resulting in 3.8 pounds of 
nitric nitrogen per inch of water, while where 15 inches of water was 
applied it was 1.1 pounds of nitric nitrogen per inch of water applied, and 
when 25 inches of water was applied to the soil the nitric nitrogen pro¬ 
duced was only 0.7 pound. 
Miinter and Robson (4) found that horn meal decomposed more rapidly 
in dry sandy soil than in clay or loam, while with higher moisture content 
there w T as little difference. Ammonium sulphate transformation in¬ 
creased with a higher water content. The best nitrate formation from 
horn meal occurred in sandy soils. In clay and loam it was best with a 
