LEAFLET No. 51
NOVEMBER 1956
T IS I tee
THAT COUNTS
Buying fertilizers according to
crop needs is good business
ALL 100-pound bags of fertili-
zers may look alike and weigh
the same, but there similarity
ends!
Each grade of mixed fertilizer
has different amounts 
of plant
food elements that determine
value and usefulness.
In selecting and buying a fer-
tilizer, these three considerations
are important to you:
1. Amount of plant food con-
tained.
2. Cost per pound of plant food
elements.
3. Proportion of the elements.
These points have a direct
bearing on returns from money
spent for fertilizer.
Fertilizer grade is expressed
by a series of three numbers. The
first figure refers to percentage
of nitrogen (N), second to per-
centage of phosphate (P
2
0
5
), and
third to percentage of potash
(K
2
0). For example, 4-12-12
contains 4 per cent N, 12 per cent
P
2
0
5
, and 12 per cent K
2
0. These
amounts add up to 28 per cent
plant food, which is a third more
than the 21 per cent plant food
in 4-10-7.
FERTILIZER COSTS COMPARED
Fertilizers having a high per-
centage of plant food usually are
better buys than grades of lower
analyses. This is the case when
grades are compared on the basis
of cost per pound of plant food.
Cotton fertilization is a good
STATION
INSTITUTE
Auburn, Alabama
AGRICULTURAL EXPERIMENT
ojle ALABAMA POLYTECHNIC
E. V. Smith, Director
IIC~U ~Alli~cr ~rl V ~rrrv ~rr uu v~ r----- -
example of how fertilizer costs
may be cut by using the right
grade. On most Alabama soils,
cotton needs 50 to 60 pounds per
acre each of N, P
2
0
5
, and K
2
0.
Using 4-10-7 as many Alabama
farmers do, it is impossible to get
equal amounts of phosphate and
potash because the percentages
are not the same.
To furnish enough potash (50
to 60 pounds) requires about 800
pounds of 4-10-7. However, this
amount supplies 80 pounds of
phosphate, which is 20 pounds
more than needed. To use less
than 800 pounds would not supply
enough potash for top yields.
On the other hand, 500 pounds
per acre of 4-12-12 fertilizer
would provide 60 pounds each of
phosphate and potash. There
would be no over supply of P20.
Now, let's compare costs of the
two grades, with N at 15 cents
per pound, P
2
0
5 
at 6 cents, and
K
2
0 at 5 cents.
800 lb., 4-10-7 + sidedressing
32 lb. N @ 15 ... --- $ 4.80
80 lb. P
2
0
5 
@ 6 ..-------------- 4.80
56 lb. K
2
0 @ 5 -------------- 2.80
Sidedressing:
28 lb. N @ 150 --------------- 4.20
Total ----------------- $16.60
500 lb., 4-12-12 + sidedressing
20 lb. N @ 150 -------------- $ 3.00
60 lb. P
2
0
5 
@ 60 ....-------------- 3.60
60 lb. K
2
0 @ 5 -------------- 3.00
Sidedressing:
40 lb. N @ 150 --------------- 6.00
Total ------------ $15.60
In each case the amount of
sidedressing is that which is
needed to bring the level of N up
to 60 pounds per acre.
At the foregoing prices, 500
pounds of 4-12-12 plus 40 pounds
of N per acre would save you $1
per acre over the cost of 4-10-7.
At many locations, 4-10-7 costs
more per pound of plant food than
does 4-12-12. Where this is true,
you save even more by using
4-12-12.
For example, in August, 1956,
a major fertilizer manufacturer
quoted prices of $37.50 per ton
for 4-10-7 and $43 per ton for
4-12-12. At these prices you
would save $2.45 per acre by
using 4-12-12.
Since fertilizer is generally
bought in large quantities, let's
look at the problem from another
angle. Three tons of 4-12-12 con-
tains 1,680 pounds of plant 
food
(N, P
2
0
5
, and K
2
0). It takes 4
tons of 4-10-7 to supply exactly
the same amount, 1,680 pounds,
of total plant food.
Not only do you supply the
right proportion of plant nutri-
ents and save money, but you
handle fewer bags of fertilizer at
planting. At the recommended
rates for cotton, you handle
about 1 ton less fertilizer for
each 7 acres by using 4-12-12
rather than 4-10-7. That amounts
to quite a saving in labor.
To determine fertilizer needs of
Alabama soils, the Agricultural
Experiment Station of the Ala-
bama Polytechnic Institute has
conducted field experiments and
soil tests in all parts of the State.
Amounts of nitrogen, phosphate,
and potash recommended are
based on results of these experi-
ments and tests. Various grades
of mixed fertilizers can be used(l
to supply the needed elements.
In general, recommendations
fall into the following three
groups from the standpoint of
kinds of fertilizer:
1. Even P
2
0
5
-K
2
0
Soil tests have shown a
this kind of fertilizer i
cent of the soils teste(
ratios and grades ar
mended:
Ratio Minimum
1-1-1
grade
8-8-8 1
1
1
1-3-3 4-12-12
0-1-1 0-14-14
2. High P20O-Low K21
zer. This kind of fe
needed in 8 per cent of
according to soil tests. I
grades recommended ar
Ratio Minimum
grade
1-4-2 4-16-8
0-2-1 0-16-8
Fertilizer. Analyses of more than 19,000
Sneed for soil samples showed a need for
in 75 per the even P
2
0
5
-K
2
0 type of fer-
d. These tilizer in 75 per cent of the cases.
e recom- Yet fertilizer sales for the fiscal
year 1954-55 included only 16 per
Multiple cent of such fertilizer. Fertili-
grades zers with an even P
2
0
5
-K
2
0 ratio
0-10-10, are needed on soils 
that are about
.3-13-13 equally balanced 
in these two ele-
ments for 
crops to 
be grown.
0-20-20 Amounts can be varied according
to the level in the soil and the
0 Fertili- crop needs.
rtilizer is
the cases,
Ratios and
Multiple
grades
0-28-14
3. Low P
2
0,-High K
2
0 Fertili-
zer. Soil tests show a need for
this kind of fertilizer in 17 per
cent of the cases. The ratios and
grades recommended are:
Ratio Minimum Multiple
grade grades
1-2-4 4-8-16
0-1-2 0-10-20
In addition to the above gener-
aliy recommended grades, others
recommended for special purposes
are:
4-12-12 (Tobacco special with
most of the potash as
potassiam sulfate and
containing not more
than 2.5 per cent chlo-
rine.)
8-8-2 (Fish pond special.)
14-0-14 (Sidedressing material
where both nitrogen
and potash are de-
sired.)
6-2-24 (Approved on trial
basis.)
Fertilizers with a high P
2
0s-
low K
2
0 ratio are needed on soils
low in phosphate and high in pot-
ash. Such fertilizers are usually
needed on Alabama soils when
they are first brought into culti-
vation. However, during years
of use of these kinds of fertilizer,
phosphate has been built up while
potash has been depleted. Hence,
a greater need for even P
2
0
5
-K
2
0
fertilizers has developed. In spite
of this change in need, 82 per
cent of the mixed fertilizers sold
in Alabama in 1954-55 was of the
high P
2
0r-low K
2
0 grades.
Fertilizers with a low P
2
0
5
-high
K
2
0 ratio are needed on soils hav-
ing high amounts of phosphate
and low potash or for crops that
have very high potash require-
ments.
The two major grades making
up the 1954-55 fertilizer sales
were 4-10-7 and 6-8-4. Besides
not being the ratio needed in the
majority of cases, both are low-
analysis materials, making it
n e c e s s a r y that considerable
amounts of filler or "make
weight" material be used in each
ton of fertilizer. In some cases a
limestone filler is used, while in
others inert material of no fer-
tilizing value is the filler. Even
when limestone is used, its cost
in the fertilizer bag is at least
twice that of what it would be if
purchased as a separate material.
Thus, it is more economical to buy
as much plant food as possible in
the fertilizer bag, and then buy
agricultural limestone as a separ-
ate material.
The Alabama State Board of
Agriculture and Industries has
ruled that 6-8-4 will not be al-
lowed for sale in Alabama after
September 30, 1956. Although
4-10-7 was retained on the list of
fertilizers approved for sale, soil
tests indicate it should be re-
placed by 4-12-12 in the majority
of cases where it is now used.
SOIL TESTS IMPORTANT
Every farmer should have his
soil tested to determine the kind
of fertilizer and the amount of
fertilizer needed. Then buy fer-
tilizer according to the plant food
contained and not solely on the
basis of price per ton. It is equally
important that soils be tested to
determine lime needs, since soil
acidity must be corrected before
maximum returns can be ob-
tained from the fertilizer used.
Farmers who have their soils
tested and lime and fertilize ac-
cording to recommendations will
receive the maximum return from
their fertilizer investment.