238 
Journal of Agricultural Research 
Vol. IX, No. 7 
amount of nitric nitrogen in. the surface scrapings. It may also be 
stated that those plots which showed a low nitrate content in the 
scrapings also showed only a few niter spots, which were a light brownish 
color and could scarcely be distinguished after the surface soil began 
to dry. 
After the third irrigation the nitric nitrogen found in the scrapings 
from the brown spots was somewhat less than after the second irrigation 
in plots A, C, G, and H, but was greater in all the other plots. It is 
seen that the nitrates in the unfertilized, lightly fertilized, and manured 
plots remain low as compared with those which have received large 
applications of nitrogen in commercial fertilizers. 
After the fourth irrigation the scrapings from plots C, F, G, M, O, R, 
and U were higher than after any previous irrigation; but in plots E, 
Q, and S the amount found is much less than during the second or 
third irrigation. Such irregularities are to be expected, as the quantity 
of nitrates in the niter spots depends upon so many variable factors, 
such as the physical character of the soil, length of irrigation period, 
rapidity with which water moves laterally in the soil, rate of evapora¬ 
tion, length of time between irrigation and sampling, distribution of 
nitrates in soil at the time irrigation is started, etc. . 
After the consideration of only the last three irrigations it was found 
that the average nitrate content of the scrapings for the five plots of light 
soil which have received heavy applications of commercial fertilizers 
amounted to 0.92 per cent of nitrogen. The average nitrate content of 
the scrapings from the two heavy soils receiving heavy applications 
of commercial fertilizers was only 0.43 per cent of nitrogen. It would 
therefore seem that surface spots high in nitrates are less likely to be 
formed in heavy than in light soils, especially if the soils are underlain 
by a rather impervious plowsole. 
The amount of nitric nitrogen found in the scrapings from plots F, O, 
and U is in striking contrast to the amount found in soils receiving the 
same or a smaller amount of nitrogen in commercial fertilizers. The 
average nitrate content of the scrapings from these three plots for the 
last three irrigations is only 0.14 per cent, which is less than one-sixth 
of the amount found in the light soils receiving nitrogen in commercial 
fertilizers. 
The surface scrapings from plots B, M, and R, which have not received 
any nitrogen, contain an average of 0.09 per cent of nitrogen for the 
last three irrigations, which is but little less than the average amount 
found in the three plots receiving organic matter, but which is less than 
10 per cent of the amount found in the scrapings from the light soils 
which have received 145.8 pounds of nitrogen in commercial fertilizers. 
The data presented above fail to indicate that the formation of niter 
spots in these soils is dependent upon the processes of nitrogen fixation 
