May 14,1917 
Soil Nitrogen and Nutrition of Citrus Plants 
235 
Some years later Headden (2) called attention to the occurrence of 
“niter spots” in Colorado soils. The occurrence of the high nitrates he 
attributed to the fixation of atmospheric nitrogen by nonsymbiotic 
bacteria. This view has been further amplified by Headden (3, 4) and 
also by Sackett (9). In 1910 Stewart (11) called attention to the occur¬ 
rence of nitrate salts in the country rock adjacent to the “niter spot” 
areas. These observations led to further studies on the nitrate content 
of the country rock by Stewart and Peterson (12, 13, 14). As a result of 
their studies these authors maintain that the “niter spots” are the direct 
result of the leaching of the nitrates out of the preexisting deposits in the 
country rock and of being locally concentrated by seepage. 
The data presented above show conclusively that the nitric nitrogen 
in furrow-irrigated soils is carried laterally from the irrigation furrows, 
causing a concentration of nitrates at the point at which the irrigation 
water meets between the furrows. If the surface soil becomes thoroughly 
moistened, as it frequently does during an irrigation, very rapid evapora¬ 
tion will occur between the moistening of the soil and the harrowing. If 
the lateral movement of the irrigation water is sufficient to cause a con¬ 
centration of nitrates in zones, such as shown above, it would seem that 
the subsequent evaporation of water from the soil in which the nitrates 
are highest would cause a marked concentration at the immediate sur¬ 
face, and thus there would be formed a “niter spot” or streak, which 
would occupy that portion of the soil in which the nitrates are concen¬ 
trated during the irrigation. Niter streaks can be readily observed in 
many groves if examined at the proper time after irrigation. They have 
a characteristic brownish appearance which varies from a light brown to 
a brownish black. The color probably depends upon a number of factors, 
among which the following seem to be important: The amount of cal¬ 
cium nitrate, the moisture content, soluble organic matter, and the presr- 
ence of other soluble salts. Where the nitrates are associated with large 
quantities of alkali salts, a brownish crust is frequently formed on drying; 
but when the nitrates predominate, the streak or spot is only readily 
seen when the surface soil contains a considerable quantity of moisture. 
After the soil has dried and the niter streaks are scarcely visible during 
the heat of the day, the color may reappear during the night if the 
weather is foggy. This phenomenon seems to point strongly to the deli¬ 
quescent character of the calcium nitrate as an important factor in pro¬ 
ducing the brown coloration.. The importance of deliquescent salts in 
this regard is also suggested by the action of calcium chlorid, which 
produces a surface color so similar to that produced by the calcium ni¬ 
trate that the writer has been unable to distinguish one from the other. 
When the nitric nitrogen in the spot amounts to 1 per cent or more, the 
deliquescent character of the salt seems to attract and hold small globules 
of water which glisten in the sunlight, giving the small spot in which the 
calcium nitrate has concentrated a silvery appearance. During hot, dry 
