9 X0 
Journal of Agricultural Research 
Vol. V, No. 20 
Southern Bessarabia has an annual precipitation of about 15 inches, 
most of it falling during the growing season. Such a climate in this 
country is commonly referred to as “semiarid.” 
Eoughridge (12, p. 87), in a comprehensive study of the distribution 
of humus in California soils to a depth of 12 feet, made nearly 1,000 
determinations of humus nitrogen, stating that— 
of these there were about 64 where the humus was found to contain more than 10 
per cent nitrogen, fourteen of these had from 15 to 20 per cent and but five had 
more than 20 per cent. . . The general average for all the soils, including the marsh 
lands, is 5.92 per cent for the first foot, 5.60 per cent for the upper three feet and 5.57 
per cent for the entire depth of twelve feet. 
Our work was an outgrowth of previous investigations in the same 
laboratory of the humus of semiarid soils. Samples from the semiarid 
prairies of Canada had been found by Alway and Trumbull (3) and Alway 
and Vail (4) to show percentages of nitrogen in the humus similar to 
those in soils from humid regions. In subsequent, as yet unpublished, 
studies by Alway and Trumbull and by ourselves many surface soils, 
representing various soil types and the different degrees of aridity found 
in Nebraska as well as many samples from the semiarid and desert por¬ 
tions of New Mexico and Arizona, were analyzed without finding even 
one in which the humus contained as much as 10 per cent of nitrogen. 
The question then naturally arose as to,whether we would meet with 
similar results if we worked with arid soils from a region of winter rains 
and summer droughts. Having available a small collection of samples of 
California soils personally collected in 1909 by one of us in connection 
with another study, we subjected these to analysis. As our analyses were 
not fully confirmatory of Hilgard’s conclusions, we delayed publication 
of the results, hoping to be able to continue the work with a more exten¬ 
sive series of samples from California. Since then, Loughridge (12) has 
reported his findings, with which ours are in general agreement. The 
question as to the conditions under which a high content of nitrogen in 
the humus is found in arid soils does not appear as yet at all satisfactorily 
answered. We present our data in the hope that some one more conven¬ 
iently located for the collection of the necessary samples will take up 
the study. 
The data upon which Hilgard’s conclusions were based are given in the 
Annual Reports of the Agricultural Experiment Station of the University 
of California from 1884 to 1902. The method used for the determination 
of humus nitrogen is described by Hilgard (7, p. 247) and Jaffa (11, p. 35): 
“Two portions of 5 or 10 grams of air-dried soil (depending on richness in 
humus)” were placed in prepared filters, washed first with dilute (0.5 to 
1.0 per cent) hydrochloric acid, until the filtrate gave no reaction for lime 
and magnesia, and then with distilled water to neutral reaction. Then 
the one portion was washed with repeated portions of 6 to 7 per cent 
ammonia solution until the washings became colorless while the other 
