4. BULLETIN 499, U. S. DEPARTMENT OF AGRICULTURE. 
The accumulation of the soluble soil constituents near the surface 
is strikingly in evidence during the summer months in almost any 
heavily fertilized grove under furrow irrigation. The sides of the 
furrows and the surface of the ridges between the furrows will be 
found coated with a brown crust which closely resembles an ordinary 
“alkali ” crust as seen in saline districts. This crust has been found 
by Breazeale to be so rich in soluble salts that it will ull young seed- 
ling oranges or lemons, the seedlings sometimes dying overnight. 
The soils of the area-do not normally contain enough soluble matter 
to bear any resemblance to “ alkali” soils; but these surface crusts 
illustrate very strikingly the tendency under this system of fertili- 
zation and irrigation of the soluble constituents to move into and 
accumulate in the surface soil. 
PLOWSOLE. 
Furrow irrigation and intensive surface cultivation often promote 
the formation of a “ plowsole,” or incipient hardpan, under the soil 
mulch, varying in thickness from 3 inches to 2 feet. This layer 
of soil beneath the mulch frequently becomes so hard as to polish 
under the point of the plow when the irrigation furrows are opened. 
A long time is required for irrigation water to penetrate it, and it 
offers a serious obstacle to the development of the roots of citrus 
trees. Deep plowing loosens the plowsole temporarily, but destroys 
the roots to the depth cf plowing, and the plowsole soon forms again. 
ORGANIC MULCHING. 
The study of the cause of mottle-leaf led to experiments having 
as their object the development of a method of fertilizing and irrigat- 
ing citrus trees which would avoid the objections of the present sys- 
tem. The use of surface mulches of organic material, such as straw, 
manure, damaged alfalfa, etc., as a substitute for the intensive culti- 
vation was suggested in 1912 by one of the writers as a possible solu- 
tion of the problem.t A trial of the organic surface mulch was 
inaugurated in 1913 on a small field plat of lemons on the Limoneria 
Ranch near Santa Paula, Cal. Under date of February 24, 1915, 
Mr. James Culbertson, assistant manager of the Limoneira Co., re- 
ported upon this experiment as follows: ; 
You will doubtless remember our discussion ...a year ago last December 
when the possible value of mulching as a corrective for chlorosis was the topic. 
Upon reaching home I had three short rows thoroughly mulched, one with 
sawdust, one with bean straw, and the third with fairly well rotted manure. 
They were not in the worst affected areas. Later in the spring, in May, when 
1 At a meeting of the California Lemon Club, at which this idea was advanced, Prof. 
H. S. Fawcett, of the University of California Citrus Experiment Station, reported an 
orange grove on an island near the eastern coast of Florida that for many years had — 
been successfully operated under the mulching system without cultivation; and he has — 
since observed the organic mulch in use in Cuba. g 
