184 Journal of A gricultural Research voi. ix, no. 7 
extensively, can not be depended upon to cause a downward movement 
of the soluble salts from the surface soil, the problem of securing a proper 
distribution of nitric nitrogen in Citrus soils at once suggests itself. 
In many soils a dense plowsole is formed during the irrigation season. 
The plowsole retards the downward movement of the water, which, 
under the furrow system, is applied in small streams, several feet apart 
and several inches below the surface. As the downward movement of 
the irrigation water is interrupted until the plowsole is softened, which 
frequently requires several hours, the water moves laterally and upward, 
not only causing a very uneven distribution of nitrates, but carrying 
them farther away from the feeding roots. It is therefore obvious that 
the satisfactory solution of the nitrogen problem in semiarid soils, and 
especially in furrow-irrigated soils, not only depends upon a knowledge 
of the factors influencing nitrification, but upon the forces controlling 
the distribution of nitric nitrogen, which is presumably the most valuable 
source of nitrogen for crops. 
ARRANGEMENT OF EXPERIMENT PLOTS 
The major portion of the work presented in this paper has been 
carried out on the soils of the Citrus Experiment Station grove, at River¬ 
side, Cal.; and it therefore seems desirable to include a brief description 
of the field and also a diagram (fig. 1) showing the arrangement of plots 
and the fertilizer applied. 
The experimental field was laid out from virgin land in April, 1907. 
The arrangement of the field is such that each plot is surrounded on all 
sides by a guard row which effectively prevents the treatment on one 
plot from influencing the trees on any other. The irrigation of each 
plot is separate, and no waste water or tailings from one plot is allowed 
to pass to any other part of the grove. 
In planning the experiment a uniform system of fertilization was 
adopted and each plot has been given the same kind of fertilizer each 
year, the quantity applied increasing in amount with the development 
of the trees. During the last four years plots A, C, G, H, L, Q, and S 
have received each year 1.35 pounds of nitrogen per tree. As there are 
108 trees per acre, the applied nitrogen amounts to 145.8 pounds for 
each acre of land. Plots F and O have received approximately the same 
quantity of nitrogen in manure until the last year, when the amount 
applied was in excess of the amount applied to the above-mentioned 
plots. Plots U and V, which were not originally included in the fertilizer 
experiment, have received moderate applications of manure in addition 
to a cover crop of vetch each year. Plots E, K, N, and P have received 
each year during the last four years about 0.45 pound of nitrogen per 
tree, or about 48.6 pounds of nitrogen per acre. Plots B, D, I, J, M, R, 
and T have received no nitrogenous fertilizers at any time. 
