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manure-treated plots, and additional treble superphosphate broadcast where the
light rate had been broadcast initially.
This second test was located at the Fink
Ranch on the west side of the Antelope
Valley. Each plot was one-third acre in
size and there were four replications of
each treatment. Results the first season
showed slightly higher yields from the
high rate of treble superphocphate than
from the dairy manure. However, as the
experiment continued, yields from the
animal manure treatments improved, particularly at the higher rate (19 tons) of
broadcast application. Results over a
four-year period (see table 3) indicate
that about 80 lbs of hay were produced
from each pound of fertilizer phosphorus
applied from the dairy manure. An equivalent yield was possible where broadcast
applications of phosphorus (from treble
superphosphate) had been made. The
heavy initial application of superphosphate worked into the soil was not quite
a? effective as the experiment Continued.
Results of these two alfalfa fertilizer
tests in the Antelope Valley indicate that
animal manures and poultry manures can
he used in alfalfa production and that
they give continued phosphorus responses
equal to, or slightly better than, those ohtained from commercial phosphorus materials. No attempt is made in this study
to evaluate costs. Nothing in the data suggests that application of manure justifies
an appreciably higher price per unit of
phosphorus than would be paid for superphosphates.
Manures in this study did at least as
well as commercial phosphorus and appear to have a definite place in phosphorus-deficient areas. If manures can be
transported and applied to the land at
favorable costs it would seem worthwhile
to explore the possibility of utilizing the
large resources of manures from poultry
farms and dairy or beef feed lots in southern California as a means of building up
some of the phosphorus-deficient soils in
nearby valleys. It would also seem possible that grass crops such as Sudan or
sorghum might precede the alfalfa to allow some return for the large amounts of
nitrogen which come with the phosphorus
in the initial manure applications-and
let the residual build-up of soil phosphorus help alfalfa crops which could
then follow.

D . M . May is Farm Advisor, Fresno
County; and W . E. Martin is Extension
Soils Specialist, University of California,
Davis.

GIBBERELLIN RESEARCH
WITH CITRUS
C . W. COGGINS, J R .

H. Z. HIELD
I. L. EAKS

R. M. BURNS

L. N. LEWIS

Gibbere...
manure-treated plots, and additional tre-
ble superphosphate broadcast where the
light rate had been broadcast initially.
This second test was located at the Fink
Ranch on the west side of the Antelope
Valley. Each plot was one-third acre in
size and there were four replications of
each treatment. Results the first season
showed slightly higher yields from the
high rate of treble superphocphate than
from the dairy manure. However, as the
experiment continued, yields from the
animal manure treatments improved, par-
ticularly at the higher rate
(19
tons) of
broadcast application. Results over a
four-year period (see table
3) indicate
that about
80
lbs of hay were produced
from each pound of fertilizer phosphorus
applied from the dairy manure. An equiv-
alent yield was possible where broadcast
applications of phosphorus (from treble
superphosphate) had been made. The
heavy initial application of superphos-
phate worked into the soil was not quite
a? effective
as
the experiment Continued.
Results
of
these two alfalfa fertilizer
tests in the Antelope Valley indicate that
animal manures and poultry manures can
he used in alfalfa production and that
they give continued phosphorus responses
equal to, or slightly better than, those oh-
tained from commercial phosphorus ma-
terials. No attempt is made in this study
to evaluate costs. Nothing in the data
sug-
gests that application of manure justifies
an appreciably higher price per unit of
phosphorus than would be paid for super-
phosphates.
Manures in this study did at least as
well as commercial phosphorus and ap-
pear to have a definite place in phos-
phorus-deficient areas.
If
manures can
be
transported and applied to the land at
favorable
costs
it would seem worthwhile
to
explore the possibility of utilizing the
large resources of manures from poultry
farms and dairy or beef feed lots in south-
ern California
as
a
means
of
building up
some of the phosphorus-deficient soils in
nearby valleys. It would also seem pos-
sible that grass crops such as Sudan or
sorghum might precede the alfalfa to al-
low some return for the large amounts of
nitrogen which come with the phosphorus
in the initial manure applications-and
let the residual build-up of soil phos-
phorus help alfalfa crops which could
then follow.
D.
M.
May
is
Farm Advisor, Fresno
County; and
W.
E.
Martin is Extension
Soils
Specialist, University
of
California,
Davis.
GIBBERELLIN
RESEARCH
WITH
CITRUS
C.
W.
COGGINS,
JR.
H.
Z.
HIELD
R.
M.
BURNS
I.
L. EAKS L.
N.
LEWIS
Gibberellic acid
is
registered and recommended in California for certain uses
(particularly in delaying rind and fruit maturity) on navel oranges and lemons.
Favorable responses have also been obtained on limes and mandarins, but
our
present knowledge
is
insufficient to warrant registration or recommendation for
use on these fruits.
So
far, we do not know how
to
take advantage of the delayed
softening and aging of Valencia orange and grapefruit rind tissue without obtain-
ing considerable regreening. The influence of
GA,
on retention of young fruit has
potential value, but no practical method has yet been devised to avoid phytotoxic
responses.
IBBERELLIC
ACID
(GA,)
is
the com-
G
mercially available member of a
family
of
naturally occurring compounds.
Very low concentrations of these com-
pounds possess biological activity capable
of regulating plant growth. The influence
of
GA,
on citrus has been the subject of
extensive field and laboratory research
in California during the past eight years.
When
GA,
is
applied to nearly mature
green-colored citrus fruit there
is
a
con-
siderable delay in loss
of
green chloro-
phyll pigment from the rind. In lemons
and limes, this reflects
a
delay in fruit
maturity, but for grapefruit, mandarins,
and both navel and Valencia oranges, the
effect appears to result from
a
delay in
certain aging processes
of
the rind.
Lemons and
limes
Preliminary trial applications of
GA,
to lemons and limes in
1956
indicated
that it might be effective in increasing
fruit set or retention in these and other
varieties of citrus. Although increased
retention occurs when
GA,
is
applied to
branches, to individual flower clusters,
or
to small fruit, phytotoxic effects occur
when
GA,
is applied to entire trees during
bloom.
The natural pattern of lemon and lime
fruit maturity
is
for much
of
the fruit to
color and ripen prior to the demand for
fresh fruit that develops during hot sum-
mer weather. GA, sprays delay the ma-
turity of lemon and lime fruits-provid-
ing greater flexibility in harvesting and
marketing. In some trials, this delay in
fruit maturity has eliminated the early
harvest, which is predominately unde-
sirable, small, tree-ripe fruit.
GA,
has
been registered and recommended for
use
on lemons since November 1963, but reg-
istration has not yet been obtained for
limes.
Mandarins
Poor fruit set
is
a
problem in the
Clementine (Algerian) mandarin where-
ever it
is
grown. In previous trials
(1958)
,
applications of
GA,
at
1,000
ppm
to
flowers in full bloom on Clemen-
tine trees resulted in increased fruit set.
The GA,-treated fruits were significantly
smaller-probably because they were
also seedless. Since the self-incompatibil-
ity of this variety can be somewhat over-
come by interplanting other citrus varie-
ties, and since spraying entire trees dur-
ing the flowering season has phytotoxic
results, very little additional research has
been performed. The potential of
GA,
to
CALIFORNIA AGRICULTURE, JULY,
1966
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