RELATION OF BACTERIAL TRANSFORMATIONS OF SOIL 
NITROGEN TO NUTRITION OF CITROUS PLANTS 
By Karl F. Kellerman, Physio logist in Charge , and R. C. Wright, Scientific Assistant , 
Soil-Bacteriology and Plant-Nutrition Investigations , Bureau of Plant Industry 
It is practically certain that there are a number of immediate causes 
for the decrease in the yield of fruit and for the general physiological 
decadence of citrous trees apparent in small areas scattered throughout 
the orange belt in California, In this region, as in many irrigated orchard 
districts of both deciduous and citrous trees, a high yield of fruit is corre¬ 
lated with a very luxuriant and vigorous vegetative growth of the indi¬ 
vidual trees. To an observer accustomed to the orchards of the humid 
regions of the East, this simultaneous enhancement of both the repro¬ 
ductive and vegetative functions of the plant suggests an abnormality 
due to a general physiological stimulation slightly in excess of the opti¬ 
mum caused by high temperature, excessive insolation, extreme fluctua¬ 
tions in quantity of soil moisture, and an abundant, though perhaps 
erratic, supply of soil nutrients. Under such conditions a very slight 
additional stimulus might cause rapid deterioration or injury. While 
this premise is not essential to the establishment of a relation between 
changes in soil nitrogen and abnormal nutrition, to recognize this unusual 
parallel of functions as signalling distinct overstimulation gives a logical 
reason for expecting similar or identical symptoms of malnutrition in 
different citrous groves, even though the immediate causes of their 
decadence within different limited areas might differ widely. 
Extensive bacteriological studies upon soils near Riverside, Cal., and 
occasional examinations of soils of other irrigated regions, together with 
observations upon the physiology of citrous trees and physiological 
experiments upon citrous seedlings, are believed to offer defensible 
hypotheses for advising the employment of certain methods of crop 
culture to ameliorate at least a portion of the baffling trouble in southern 
California generally known as citrous malnutrition, chlorosis, or mottle 
leaf (Smith and Smith, 1911). 1 
A careful examination of the soluble-salt content 2 of soil samples 
taken throughout southern California showed in common with other 
investigators (Hilgard, 1906b; Swingle, 1904; Eoughridge, 1903, 1911; 
1 Bibliographic citations in parentheses refer to "Literature cited, ” p. 113. 
2 Except for the estimation of nitrates, determinations were made in accordance with the methods de¬ 
scribed by Schreiner, O., and Failyer, G. H., Colorimetric, turbidity, and titration methods used in soil 
investigations, U. S. Dept, of Agr., Bur. Soils Bui. 31. Nitrates were determined by a modification of the 
Thieman-Schultze method, for explanation of which see Kellerman, K. F. f and Smith, N. R., The 
absence of nitrate formation in cultures of Azotobacter, Cent. f. Bakt. [etc.], Abt. 2, Bd. 40, No. 19/21. P. 
479-482. 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
(101) 
Vol. II, No. , 
May 25, 1914 
G—20 
