Feb. 26,1917 
Effect of Water and Manure on Nitrates in Soils 
347 
The tendency for the salts to decrease with depth is much more marked 
in the fallow plots than in the cropped, although with no water and 40 
inches for the fallow soil the tendency is hardly noticeable. 
As an average the difference in total salt content between fallow and 
cropped soils was least noticeable on the unirrigated plots and increased 
with the water applied up to 30 inches. Only 41 p. p. m. more salts 
were in the fallow than in the cropped soil for an application of 40 inches 
of irrigation water. The fallow plots differ from the cropped more 
where the manuring was 5 tons to the acre than for the other treatments. 
The difference is also more pronounced for the top feet than for the 
lower ones with applications of no manure and 5 tons, although for 15 
tons the lower feet of the two treatments differ most. 
Fig. 11.—Graph showing the nitrates in the fall in cropped soil receiving different quantities of manure 
and irrigation water. Average of 3 years to a depth of 10 feet. 
Tor most irrigation treatments the total soluble salts in the top foot 
of the cropped and fallow soils differed considerably more than the 
average for all feet. This is much more noticeable for the plots receiv¬ 
ing 30 inches than for the others both in the first and second foot. 
Tables II and III summarize the effects on soluble salts of manure 
and moisture separately in both cropped and fallow soil. 
NITRATES IN CROPPED SO IE 
The nitrates, expressed as sodium nitrate in parts per million of dry 
soil, found in the same plots as discussed above, are shown in Table IV 
and figures n and 12. 
Only when the application of water was 40 inches did the nitrates of 
the cropped plots receiving 5 tons of manure exceed those of unmanured 
plots, and in this case the difference was small. The greatest variation 
between the two was for no water. Although the greatest average 
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