May 2s, 1914 
Transformations of Soil Nitrogen 
109 
(Hilgard, 1906a)—exert a more or less pronounced protective action. 
Sulphates are comparatively innocuous and are not reported upon. In 
this connection it should be noted that while, as would be expected from 
the analogy of California soils with the soils of the citrous regions of 
Florida, rather large quantities of calcium carbonate are favorable to 
the citrous plants, even slight traces of calcium oxid or calcium hydrate 
have an immediate toxic effect. The beneficial effect of calcium car¬ 
bonate in flocculating the impervious soils and thus facilitating their 
permeability to irrigation water renders it valuable from a physical as 
well as a biological standpoint in many areas. 
While no adequate data are recorded, records of at least temporary 
benefit from the application of nitrate fertilizers to chlorotic orange 
groves are available. Laboratory and greenhouse studies offer a possi¬ 
ble explanation of such a phenomenon under certain conditions. As 
shown in figures 5, 6, and 7, different substances which are commonly 
plowed under to maintain humus in the soil show pronounced differences 
in their effect upon the soil bacteria. Mature barley straw or pure cel¬ 
lulose rapidly reduces the nitrate content of a soil 1 and may eliminate 
it entirely if it is present in relatively small quantities; furthermore, 
although but little nitrogen is actually lost, it seriously delays the reni¬ 
trification into nitrate. Green manures, on the other hand, while causing 
some actual loss of total nitrogen, do not materially disturb the ratios of 
the nitrogenous compounds. The same order of limitation is shown by 
these substances in their effect upon the nitrification of pepton in the 
soil. As shown in Tables IV and V, seedling citrous plants were actually 
forced by the addition of cellulose and of straw into an apparently 
typical state of malnutrition through nitrogen starvation caused by the 
unbalancing of the soil flora and the utilization of all of the nitrate by 
the organisms which decompose straw and cellulose. 2 
1 Prom unpublished results in 1911. Any mature straw, as well as pure cellulose, causes a rapid denitri¬ 
fication of soil nitrate, and the subsequent nitrification which again forms nitrate is very slow, (See 
also Lipman, J. G., and Brown, Percy E., 1909.) 
8 From unpublished results in 1907, showing injury to com by the bacterial denitrification of nitrate 
to nitrite, it was supposed that nitrite poisoning might be the cause of the injury to citrous plants in the 
conditions shown in Table V. The presence of appreciable quantities of nitrite in the soil supporting 
apparently normal citrous plants indicates that complete elimination of nitrate is more injurious to them 
than is the formation of slight quantities of nitrite. 
41217 14—3 
