336 
Journal of Agricultural Research 
Vol. IX, No. 9 
in the fallow, which is not cultivated. The crop in every case increases 
the number of organisms, and this in direct relation to the plant residues 
left on the soil. However, we find the ammonifying powers varying in the 
opposite order. The nitrifying powers are increased by the alfalfa and 
potatoes. Hence, we can conclude that the alfalfa not only feeds closer 
upon the soluble nitrates of the soil but also makes a much greater drain 
upon the insoluble nitrogen of the soil by increasing its nitrifying powers. 
It therefore would deplete the soil if the entire crop be removed, more 
readily than would any of the other crops. 
The application of water has decreased the nitric nitrogen found in 
the 6 feet of surface soil, but has slightly increased the nitrous nitrogen 
of the soil, while the number of organisms remain about the same in all 
the soil except those receiving 37.5 inches of water, and in these the 
number decreases. The ammonifying powers of the soil are slightly 
increased by the water, while the nitrifying powers are very uniform. 
But this holds only for the fall, for during the spring we obtain the 
following results for nitrifying powers: 
Per cent. 
No water. 100 
15 inches of water. 125 
2 5 inches of water. 115 
37.5 inches of water. 135 
The nitrogen removed in the crop increases, but not in the same pro¬ 
portion as does the ammonifying and nitrifying powers. Furthermore, 
we have a rapid decrease in the nitric nitrogen of the soil. Especially is 
this true where the larger quantities of water are applied. The results 
therefore indicate that the effect of the excessive use of irrigation is not 
only a waste but the yield of the crop is depressed, and the depressed 
yield is due to the water carrying the soluble nitrates beyond the sphere 
of action of the plant roots. Furthermore, it increases the ammonifying 
and nitrifying powers of the soil during the spring and summer, with the 
result that a greater quantity of soluble plant food produced is carried 
out by the drain waters, and the soil is to this extent needlessly depleted 
of its nitrogen. 
SUMMARY 
The quantity of nitric nitrogen in the surface 6 feet of alfalfa soil is 
comparatively low throughout the season, but is higher in the fall than 
in the spring or summer. The quantity present decreases as the water 
applied increases; yet the quantity formed in the soil increases as the 
water applied increases, but is greatest per acre-inch of water when only 
15 inches of water are applied. 
The quantity of nitric nitrogen in the surface 6 feet of potato, oats, 
com, and fallow soil decreases as the water applied increases; but the 
quantity formed for each of the cropped soils is greatest where the largest 
quantity of water was applied. The quantity formed per acre-inch of 
water applied is greatest where only 15 inches of water were applied. 
