TEXAS AGRICULTURAL EXPERIMENT STATION

C. H. McDOWELL, Acting Director
College Station, Texas

BULLETIN NO. 672

JULY, 1945

THE VALUE OF DIFFERENT PHOSPHATES FOR
VARIOUS TEXAS SOILS AND GRASSES, AS
INDICATED BY POT EXPERIMENTS

J. F. FUDGE AND G. S. FRAPS

Division of Chemistry

 

AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS

GIBB GILCHRIST, President

J fir)’ “--.:]

E72-745-3500-L180

[Blank Page in Original Bulletin]

The effects of kind and amount of phosphates, kind of soil, and
kind of grass upon the yield and phosphoric acid content of several
grasses were studied by means of pot experiments in the green-
house. ‘

Superphosphate greatly increased either the yield or the per-
centage of phosphoric acid in the dry matter or both yield and
percentage. The increases in yield were greater where the soils
were more deficient in active phosphoric acid. Small applica-
tions of superphosphate often produced large increases in yield
accompanied by only small increases in percentage of phosphoric
acid in the dry matter. Larger applications produced large in-
creases both in yield and in percentage of phosphoric acid, rais-
ing the percentage well above the minimum required for range
animals. Ditferent species of grasses differed in their capacity

to utilize soil phosphates; dilferences among the grasses were re- .

duced by the application of superphosphate. A large part of the
phosphoric acid added in superphosphate was recovered in the crops.

Ground rock phosphate increased yields in a few cases but had
little elfect upon the percentage of phosphoric acid in the dry mat-
ter. Increasing the amount of rock phosphate, the period of contact
with the soil, or the fineness of grinding did not cause any further
increases in yield or percentage. Ground rock phosphate is not

to be recommended for use on pastures.

CONTENTS
PAGE
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  . . . . . . . . . . . . . . . . . . . .. 5 f

Previous work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 5 5

Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. sl

Effect of kind of soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 9 *

Effect of phosphates on different kinds of grasses . . . . . . . . . . . . . . . . . . .. 13o

Effect of phosphates on yield and composition at diiferent dates . . . . .. 17 

Recovery of phosphoric acid in superphosphate compared with that in
rock phosphate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 19 p

Effect of different amounts of phosphates on yields and composition of J
grasses . . . . . . . . . . .' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 '

Value of other phosphates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2O ',

Discussion . . . . . . . . . . . .’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

Superphosphate , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

Rock phosphate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 22 a

Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 ‘p

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Iiiterature cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 24 i

THE VALUE OF DIFFERENT PHOSPHATES FOR VARIOUS
TEXAS SOILS AND GRASSES, AS INDICATED
BY POT EXPERIMENTS

J. F. Fudge, Chemist, and G. S. Fraps, Chief,
Division of Chemistry

The importance of phosphatic fertilization of pastures has been shown
by many investigators in recent years, following work which showed that
the percentage of phosphoric acid in forage is an important limiting
factor for satisfactory animal production in many areas (3, 5, 15, 16, 29,
40, 42). Studies in Texas have shown that many soils are deficient in
phosphoric acid (19), that many grasses produced on these soils are
deficient in phosphoric acid (20, 21, 26, 27), and that the percentage of
phosphoric acid in young forage is closely related to the supply of phos-
phoric acid in the soils (22, 24, 25, 26, 27).

The question of the phosphatic fertilization of pastures in Texas is of
immedate practical importance. It was therefore considered desirable
to secure further information concerning the effect of different phosphates
on grasses on different kinds of soils. In order to secure more complete
control over various factors which affect plant growth than is possible
under field conditions, this study was made by means of pot experiments
in the greenhouse.

Several carriers 0f phosphoric acid are available for use as fertilizers.
Superphosphate is the most important and widely used of these carriers.
Phosphoric acid in superphosphate has a high availability. Rock phosphate
is also obtainable in large quantities, but many investigators have shown
that phosphoric acid in rock phosphate is not nearly as available to most
plants as that in superphosphate. Calcium metaphosphate and ammonium
phosphate may come on the market. Limited amounts of defluorinated
rock phosphate are now being used on pastures.

Previous Work

The application of superphosphate to pastures often results in in-
creased yields of forage, but even where increases in yield are small, the
percentage of phosphoric acid in the forage may be increased sufficiently
to warrant the use of the fertilizer. Increases in yield and phosphoric
acid content following the use of superphosphate may differ widely on
different soils and with different plants. Data presented in Table 1, taken
from several publications, illustrate these points. u

Superphosphate not only increases the phosphoric acid in the species
already present in the pasture, but often promotes the growth of more
desirable species of forage, particularly legumes, which are relatively
high in protein and phosphoric acid.

 

 

 

 

   

 

Table 1. Eflect of superphosphate upon yield and percentage of phosphoric acid in forage in field experiments
Yield of Dry matter Phosphoric acid
_ Tons per acre in dry matter Reported in
State Crop Soil series _ _ literature

Not _ _ Not Fertilized cited

fertilized Fertilized fertilized % % No.

Alabama . . . . . . . . . . . . . . .. Herbage............ l1ouston............ . . . . . . . . . . . . . . . . . . . . . . .. .41 .69 31

Herbage . . . . . . . . . . . . Eutaw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23 .44 i 31

Herbage . . . . . . . . . . . . Norfolk . . . . . . . . . . . . 0.63 1.04 .24 .43 32

Herbage............ Houston . . . . . . . . . . .. 1.27 .64 .37 .72 32

Herbage . . . . . . . . . . . . Decatur . . . . . . . . . . . . .54 0.93 .67 .82 32

Connecticut . . . . . . . . . . . . . . Herbage. . .. . . . . . . . . Charlton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48 .73 10

West Virginia . . . . . . . . . . . . Herbage. . .. . . . . . . . . Uekalb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38 .77 37

I'-lerbage............ Huntington......... . . . . . . . . . . . . . . . . . . . . . . .. .64 .83 37

I1erbage............ Crowley . . . . . . . . . . .. 1.31 2.70 .26 .41 2O

Washington . . . . . . . . . . . . . . Alfalfa . . . . . . . . . . . . . Hitzville. . . .. . . . . . . . 1.52 2.10 .70 .80 43

Alfalfa . . . . . . . . . . . .. Puget. . . .- . . . . . . . .. 1.69 2.17 .64 .70 43

Alfalfa . . . . . . . . . . . .. Dungeness. . .. . . . . .. 2.14 3.27 .54 .78 43

Alfalfa . . . . . . . . . . . . . Winchester . . . . . . . . . 2.67 2.57 .52 .55 43

\Visc0nsii1 . . . . . . . . . . . . . . . Alfalfa . . . . . . . . . . . . . Miami . . . . . . . . . . . . . . . . . . . . . . . . . I . . . . . . . . . . . . .46 .53 28

Alfalfa . . . . . . . . . . . . . Gilfor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38 .59 28

New Nlexico . . . . . . . . . . . . . Alfalfa . . . . . . . . . . . . . Gila . . . . . . . . . . . . . . . 5.04 7.79 .37 .47 30

Florida . . . . . . . . . . . . . . . . . . Carpet grass . . . . . . . . Bladen . . . . . . . . . . . . . 0.19 0.40 .27 .44 6

Carpet grass . . . . . . . . Bladeii . . . . . . . . . . . . . 0.20 0.43 .25 .42 7

Carpet grass . . . . . . . . Leon . . . . . . . . . . . . . . . 0.27 0.37 .39 .50 7 .

Carpet grass . . . . . . . . Plummer . . . . . . . . . . . 0.23 0.47 .44 .48 7

South Carolina . . . . . . . . . . . Carpet grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28 .40 13

Texas. '. . . . . . . . . . . . . . . . . . Carpet grass . . . . . . . . Crowley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24 .36 24

Connecticut . . . . . . . . . . . . . . Kentucky bluegrass. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49 .71 9

Maryland. . . .. . . . . . . . . . . . Kentucky bluegrass. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .89 1.12 44

Kentucky bluegrass. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82 1 .00 47

West Virginia . . . . . . . . . . . . Kentucky bluegrass. . Dckalb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37 .68 37

Wisconsin. . . . .. . . . . . . . . . . Kentucky bluegrass. . . . . . . . . . . . . . . . . . . .. 0.84 1.40 . . . . . . . . . . . . . . . . . . . . . . .. 1

Maryland . . . . . . . . . . . . . . . . White clover... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.03 1.26 44

Whiteclover........ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .84 1.02 47

Connecticut. . .. . . . . . . . . . . SWCt‘.tVCi'l1&]... . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . .. .34 .54 _ 9

West Virginia . . . . . . . . . . . . Poverty grass . . . . . . . Dckalb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24 .60 37

Broomsedge. . . . .. . . . Dekalb . . . . . . . . . . . . . . . . . . . . . . .. .29 .52 37

Kentucky bluegrass. . Dekalb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37 .68 37

'l‘e."<as . . . . . . . . . . . . . . . . . . . Angleton grass . . . . . . Lufkin . . . . . . . . . . . . . 1.72 19 .26 .34 8

Rhodes grass. . . . . .. Lufkin . . . . . . . . . . . .. 3.05 4.71 .23 .38 8

Bermuda grass . . . . . . Lufkin . . . . . . . . . . . . . 0.25 .52 .30 .41 8

 

NOLLVLS LNEINIHBJXEI TVHQLTHOIHDV SVXEIJ. 'ZL9 "ON NLLEUITDEI

 

 

VALUE OF DIFFERENT PHOSPHATES FOR TEXAS SOILS AND GRASSES 7

Lespedeza occurred in appreciable amounts on plats of a Crowley clay
loam at Beaumont, Texas (22), which had received superphosphate but
was not important on unfertilized plats. On a Connecticut pasture (9),
white clover amounted to less than 1% of the total forage on unfertilized
plats but contributed up to 55% 0f the total forage on plats which had
received superphosphate. On another area (10), Kentucky bluegrass
provided 1% of the forage on unfertilized plats, 50% on plats which had
received superphosphate, and 75% on those which had received both super-
phosphate and a nitrogen fertilizer. During a 6-year experimental period
on pastures in West Virginia (37), weeds and bare space increased mark-
edly on unfertilized plats, while Kentucky bluegrass and white clover
largely replaced less desirable grasses and weeds on plats which had re-
ceived superphosphate. Many other similar results have been reported.

The beneficial effects of superphosphate may persist on pastures for
several years after applications have been discontinued. Robinson and
Pierre (38), found beneficial effects from the use of superphosphate four
and one-half years after the last treatment. Brown (10) found that vege-
tation from fertilized plats contained 40% more phosphoric acid than
vegetation from unfertilized plats 14 years after an application of 320
lbs. of phosphoric acid in superphosphate. Ahlgren (1) found that the
yield of mature Kentucky bluegrass from plats which had received 20%
superphosphate at the rate of 400 pounds per acre five years previously
was nearly four times as great as that from the unphosphated plats.»

Rock phosphate has usually been found to be less available than super-
phosphate. Mooers (33) reported that rock phosphate gave much lower
returns than superphosphate for oats and hay, that fineness of grinding
beyond that usually employed did not increase availability, and that avail-
ability of rock phosphate did not noticeably increase on long contact with
the soil. Noll and Bechdel (34) reported that applications of rock phos-
phate carrying twice as much phosphoric acid as applications of super-
phosphate gave lower yields than superphosphate in every one of 58
comparisons conducted on pastures in Pennsylvania. Volk (45) reported
that increases in yield of hairy vetch from the use of superphosphate on
different soils were from twice to 18 times those from rock phosphate.
Fraps (17, 18) reported that the phosphoric acid in rock phosphate was
much less available than that from superphosphate. O’Brien (36) re-
ported that superphosphate was much more effective than rock phosphate
in increasing the percentage of phosphoric acid in Kentucky bluegrass and
white clover. DeTurk (14) states that phosphoric acid in rock phosphate is
not available to the plant during the critical early stage of growth, while
that in superphosphate is readily available. Brown and Jacob (12) re-
ported that superphosphate was superior to rock phosphate in all of their
work. Increasing the rate of application of rock phosphate often has
very little, if any, effect upon the yield secured (17, 45, 46). Soft rock
phosphate with colloidal clay (also called waste pond phosphate) is no
better than ordinary rock phosphate (18, 45, 46) and contains only about
two-thirds as much phosphoric acid.

   
  
   
    
  
   
   
   
    
    
 
  

8 BULLETIN NO. 672, TEXAS AGRICULTURAL EXPERIMENT STATION

Several other phosphates are or may become obtainable for use as ferti-k“
lizers. Calcium metaphosphate is made by burning phosphorus and passing;
the combustion products into rock phosphate at high temperature. De-p
fluorinated rock phosphate is made by fusing rock phosphate with silica‘!
and quenching the melt. In both of these processes, much of the fiuorinei
in the rock phosphate is removed. Phosphoric acid in these two phosphatesli
may have practically the same availability on noncalcareous soils as th
in superphosphate (2, 30, 11, 39), but they cannot, at present, be recom ~
mended on- calcareous soils. Ammonium phosphate is a soluble phosphat
in which the phosphoric acid probably has a high availability. Basic.
slag, a by-product from the manufacture of steel, has been used in many-
areas with variable results, but it contains only about 8 to 12 per cent):
of total phosphoric acid and is a low-grade fertilizer. Phosphoric acid "p14
some basic slags may be nearly as available on some soils as that in supera
phosphate (33, 35, 39). ' ~

Methods

z

In all of the Work reported in this bulletin, 5 kilograms of soil were!)
Weighed into galvanized iron pots, nitrogen and potash (1 gram each 
ammonium nitrate and potassium sulphate per pot) were added to all
pots at the start of the work in March and, in most experiments, again...
in August. Quantities of the various phosphates calculated from the.
analyses to contain the desired amounts of phosphoric acid were weighed.
out and mixed with the soil. When superphosphate was compared withfi
rock phosphate, the amount of phosphoric acid applied in rock phosphate;
was usually twicethat applied in superphosphate. A parallel series of
pots to which no phosphoric acid was added was included in all experi ‘
ments. All treatments were made in triplicate. After the fertilizer 1i
been mixed with the soil, weighed quantities of seed (or, in a few cases,
plants) were planted. Water equivalent to 50% of the water-holding-

Table 2. Composition of soils

_ Total Active Basicity i;
S011 _ phosphoric phosphoric as

No. Soil type Nitrogen acid acid CaCOs pH .2
% % p-p-m- %

49075 Lufkin fine sandy loam. . .. . . . .042 . . . . . . . . . . 61 0.3 5. _

49663 Houston black clay . . . . . . . . . . . 127 .070 213 3.6 7 "J

50300 Wilson clay loam . . . . . . . . . . . . .083 .040 49 1 .0 6. 

50301 Wilson clay loam . . . . . . . . . . . . .065 . 030 14 1. 1 5. - j

50304 Houston clay . . . . . . . . . . . . . . . .180 . 111 26 31.3 8. .

50306 Reinach silt loam . . . . . . . . . .. 0.76 0.94 458 20.0 8 ‘

52320 Houston black clay . . . . . . . .. .102 .106 34 10+ 8. ~

53798 Nimrod fine sand . . . . . . . . . . . . .024 .015 64 0.5 8. ’

53801 Abilene clay . . . . . . . . . . . . . . . . .110 .052 59 10 + 8. .

53802 Frio clay loam . . . . . . . . . . . . . . .270 . 136 449 5.0 7. ~
53804 Windthorst fine sandy loan. . . .031 .018 35 0.4 7.
53810 Blanket clay loan . . . . . . . . . .. .187 .057 60 15.1 7
54289 Norfolk fine sand . . . . . . . . . . . . .044 . . . . . . . . . . 52 0.3 5
65031 Lufkin fine sandy loam. . .. . . . .059 .025 19 0.3 5
66401 Lufkin fine sandy loam . . . . . . . . . . . . . . . . . .021 19 0.4 6. _

VALUE OF DIFFERENT PHOSPHATES FOR ‘TEXAS SOILS AND GRASSES

Table 3. Common and. botanical names of grasses used

Common name

ngleton grass _ , . . . . . . . ._. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ermuds grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . .
lack fingergrass , _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
qfialo grass _ _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

_ aroet grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

urly mesquite grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
allis grass . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
eather finger grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

_ orgia grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ohnson grass . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
'ttle bl iesiem grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . .
bodes grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Botanical name

Andropogon annulalus
Cynodon daciylon
Chloris cucullata
Buchloe dactyloides
Axonopus afiinis

H ilaria Belangeri
Paspalum dilaiatum
Chloris virgata
Paspalum plicaiulum
Sorghum halepense

4 ndropogon scoparius
Chloris gayana

L allow beard grass _ _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Paspalum malacovhyllum
Routeloua curlinendula
Eragrostis curvula
Andropogon ischaemum

_'bbed paspalum grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
rleoats grama grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
‘ eeping love grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

lapacity 0f the soil was added. This moisture content was maintained

@- weighing the pots every two or three days, making allowance for the
stimated weight of the crops, and adding the amount of water required

rops were cut from the same pot.

A Analyses of the soils used are shown in Table 2.

o bring the pots to the original weight.

The grass was usually clipped at intervals of about 6 weeks; several
At all but the final harvest, the
'_ asses were cut back to about 2 inches in height. The final harvest in-
“luded all plant material above the ground. The material harvested was
ried at about 45°C., ground in a Wiley mill, and analyzed for phosphoric
cid by the volumetric molybdate method (4).

The common and

tanical names of the grasses used are given in Table 3..

Elfect of Kind of Soil

- In order to study the effect of the kind of soil upon the response to
hosphatic fertilizers, 12 soils were selected which differed widely in
hysical and chemical characteristics. Black finger grass was grown
J first year on all these soils; Bermuda grass was grown thelfollowing
ear 0n ten of the same soils. Both grasses were grown at the same time
n two soils (65031 and 66401) used in other experiments. On black
ger grass, superphosphate (100 mgm. P105) or rock phosphate (200
in P205) Was mixed with the soil in March at the start of the work
nd a second application broadcast on the surface in August. On- Bermuda
-_ ss the following year, all of the phosphate (200 or 400 mgm. P205)
gas mixed with the soil before planting. The Bermuda grass on ten soils
A so had the benefit of the residue of the phosphate applied to black
Vger grass. Both grasses were clipped 5 times during the growing
ason, ending in November. The total yield of dry matter, the per-
‘ tage of phosphoric acid in the dry matter, and the percentage recovery
p the phosphoric acid added are shown in Table 4. -
~i Because nitrogen and potash were added, ‘the yields without phosphate
ere due chiefly to the phosphoric acid of the soil. If the conditions for

OI

Table 4. Eflect of superphosphgle (200.mgm. P205) and rock phosphate (400 mgm. P205) on totalyield of dry matter and phosphoric acid in

 

black finger and Bermuda grasses grown on different soils g

F‘

' I"

Weighted average percentage of Recovery of E1!

Total yield of dry matter phosphoric acid in dry matter phosphoric acid added E

None Super Rock None Super Rock Super Rock z

sm- sm- sm- % % % % % o

Black finger grass .1,

65031 Lufkin fine sandy loam . . . . . . . . . . . . . . . . 7.8 39.5 20. 9 23 27 .23 43.4 7 .7 g
53804 Windthorst fine sandy loam . . . .. . . . . . .. 8.3 22.5 11.1 26 28 .24 20.3 1.2 ‘

50304 Houston clay . . . . . . . . . . . . . . . . . . . . . . 14.1 48.3 18.3 25 .27 .26 47.3 3.0 ,_3

50301 Wilson clay loam . . . . . . . . . . . . . . . . 16.5 43.4 29.9 18 .28 .21 47.0 8.6 m

66401 Lufkinfine sandyloam............  20.7 68.0 38.9 22 .24 .23 60.8 13.1 >4

50306 Reinach silt loam . . . . . . . . . . . . . . . . . . . . . 22. 7 35.6 25. 1 32 .36 .30 27.6 1 .0 i>

53798 Nimrod fine sand . . . . . . . . . . . . . . . . . . .. 23.6 29.8 25.1 23 33 .26 22.6 2.0 m

52320 Ilouston black clay . . . . . . . . . . . . . . . . . . 26.4 50.5 41.3 21 24 .23 33.0 10.8 ;>

53801 Abilene clay . . . . . . . . . . . . . . . . . . . . . . . . . 27.9 49.3 32.0 23 .29 .23 39.7 2.4 c)

54289 Norfolk fine sand . . . . . . . . . . . . . . . . . . .. 30.6 33.7 27.0 27 40 .28 26.4 0 F0

49663 Houston black clay . . . . . . . . . . . . . . . . . . . 44 .4 48.8 42.0 25 .30 .25 16.1 0 6

50300 Wilson clay loam . . . . . . . . . . . . . . . . . . . . 45.3 47.4 42.7 i4 4-1 .38 19.6 1.3 c;

53802 Frio clay loam . . . . . . . . . . . . . . . . . . . . . . . 57.5 69.1 63.1 27 30 .28 27.7 5.0 r

53810 Blanket clay loam . . . . . . . . . . . . . . . . . . . 57.7 67.6 60.6 25 3 .23 38.0 1.2 g

Average . . . . . . . . . . . . . . . . . . . . . . . 28.3 4e 7 34 1 25 51 26 .55 .1 4.1 f:

Bermuda grass r.

65031 Lufkin fine sandy loam . . . . . . . . . . . . . . . .» 12.5 34.3 17.4 .24 .26 .27 29.2 4.1 [11
53801 Abilene clay . . . . . . . . . . . . . . . . . . . . . . . .. 22.2 67.9 22.4 .14 .18 .14 41.0 0 >4
66401 Lufkin fine sandy loam . . . . . . . . . . . . . . .. 22.9 69.3 55.7 .19 .23 .21 60.8 18.7 “U
53804 Windthorst fine sandy l0am............ 23.7 54.9 18.3 .15 .25 .16 51.3 0 t;
50301 Wilson clay loam . . . . . . . . . . . . . . . . . . . .. 24.0 57.9 34.9 .15 .17 .14 32.4. 1.7 >-<

49663 Houston black clay . . . . . . . . . . . . . . . . . . . 48.3 86.4 49.8 .16 .21 .14 53.4 0 S

50304 Ilouston clay . . . . . . .  . . . . . . . . . . . . . .. 52.0 77.0 52.0 .14 .19 .15 37.6 1.1 P1

50306 Reinach silt loam . . . . . . . . . . . . . . . . . . . . 54.1 81.2 54.3 .17 .26 .17 58.3 0 Z

53810 Blanket clay loam . . . . . . . . . . . . . . . . . . .. 54.6 83.1 57 .1 .17 .22 .13 44.2 0 73

52320 Houston black clay . . . . . . . . . . . . . . . . . . . 64.4 86.5 62.4 .18 .23 .17 44. 5 0 m

50300 Wilson clay loam . . . . . . . . . . . . . . . . . . . . . 77.5 89.8 79.2 . 19 .27 .20 47.0 2.9 >-]

53802 Frio clay loam . . . . . . . . . . . . . . . . . . . . . .. 100.4 11.4 97 5 21 .28 .23 48.7 4.4 g
W i-l
Average . . . . . . . . . . . . . . . . . . . . . .. 47.2 75 0 50 1 .17 23 18 45.1 2. g

 

VALUE OF DIFFERENT PHOSPHATES FOR TEXAS SOILS AND GRASSES 11

plant growth were entirely equalized, the yields in the pots fertilized with
superphosphate would be equal in the different soils on which the same
grass was grown under the same environmental conditions. Yields were
F, not equal, but ranged from 22.5 to 69.1 grams-per pot, with an average
of 46.6 grams for the black finger grass, and from 34.3 to 111.1 grams
zwith an average of 75.0 grams for Bermuda. The differences in yields
iishow that the conditions for plant growth were not entirely equalized
rby the addition of the superphosphate. Some of the soils were much more
“favorable to the growth of the grasses than others. Bermuda failed en-
tirely on two soils, though planted several times. These two soils were
a Nimrod fine sand (53798) and a Norfolk fine sand (54289), on which
superphosphate the previous year caused small increases in yield and
E considerable increases in the percentage of phosphoric acid in black finger
y, grass. Bermuda grass seldom grows well on very sandy soils in the
Efield. The relative growth on the soils was not always the same with
{the two grasses.

  

The difference in yield between finger grass and Bermuda grass indicates
that Bermuda grass may have a greater growth capacity. However, the
differences in yield cannot be assigned entirely to differences in the grasses.
They may be due partly to differences between the seasons of 1942 and
1943, partly to the fact that the superphosphate was added in two applica—
tions to finger grass and in one application to Bermuda, and partly to
residual phosphates available to the Bermuda grass.

The effect of superphosphate in increasing yields on most soils de-
‘creased as the yields of grass grown without phosphate increased. That
is, as a rule, the greater the deficiency of the soil in phosphate for the
growth of the grass, the greater was the relative effect of the super-
phosphate upon yields. Other factors interfered with this relation, as
pointed out above.

The quantity of superphosphate used considerably affected the yield of
> the grasses and only slightly increased the percentage of phosphoric acid.
.7 The application of superphosphate increased the production of grass with-

out increasing the phosphoric acid content sufficiently to meet the re-
quirements of grazing beef animals (0.33%) in 22 of the 26 tests. In 4
7 of the tests, the percentage of phosphoric acid was increased sufficiently for
(this purpose. The black finger grass grown on the Reinach silt loam,
Nimrod fine sand, Wilson clay loam and the Norfolk fine sand contained
isufficient percentages of phosphoric acid (over 33%) but Bermuda grass
‘on all soils did not. Yields of Bermuda grass were much greater than
yields of black finger grass. The application of a limited amount of
superphosphate, although increasing the yield, may not greatly increase
the percentage of phosphoric acid in the grasses. Other work presented
lVlater shows that this increase may be secured when sufficient quantities
of superphosphate are applied. '

Rock phosphate produced much smaller increases in yield and percentage
of phosphoric acid in the grasses than those produced by superphosphate.

 

ZI

a

Table 5. Relation of chemical composition of soils to respone of black finger grass to application of superphosphate

Total yield in Increase in Phosphoric acid Phosphoric acid . Increase in
dry matter yield due to in dry matter in dry matter phosphoric acid
Level of constituent in soils phosphate due to phosphate i
None Super gm. None Super None Super mgm.
‘ gm. _ gm. % 0 mgm. mgm.
Active phosphoric acid
0t030p.p.rn . . . . . . . . . . . . . . . .. 14.8 49.8 35.0 .20 .26 29.6 128. 99.2
31 to 100 p.p.m . . . . . . . . . . . . . . .. 31.4 43.0 1‘l.6 .26 .32 81.4 138. .
Over 100p.p.m . . . . . . . . . . . . . . . .. 41.5 51.1 9.6 .28 .32 116.4 154.0 37.6
Total phosphoric acid
0to.050% . . . . . . . . . . . . . . . . . . .. 26.3 44.1 17.8 .25 - .31 66.6 136.1 69.5
.051 t0.lOO% . . . . . . . . . . . . . . . .. 31.7 44.6 12.9 .26 .32 83.0 138.5 55.5
Over .100% . . . . . . . . . . . . . . . . . .. 32.7 56.0 23.3 .25 .27 81.8 153.5 71.9
Basicity - \
Under 2% . . . . . . . . . . . . . . . . . . . .. 26.3 44.1 17.8 .25 .31 66.6 136.1 69.5
Over2% . . . . . . . . . . . . . . . . . . . . .. 32.2 50.3 18.1 .26 .29 82.4 146.1 63.7

i800
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NOLLVLS JJNEINIHEIJXEI TVHIICUIHOIZIDV SVXHL 'ZL9 ‘ON NIJJEVYIHH

    

VALUE OF DIFFERENT PHOSPHATES FOR TEXAS SOILS AND GRASSES 13

The increases due to rock phosphate are so 10w that the use of rock phos-
phate is not justified.

The percentage of the added phosphoric acid recovered from super-
phosphate averaged 33.5% with black finger grass and 45.2% with Bermuda
grass. The apparently higher recovery by Bermuda grass may be due
in part to phosphate residues from the preceding year. Recovery of
phosphoric acid from rock phosphate averaged 4.1% and 2.7%, but the
average would be much lower than this, if the 3 tests in which recovery
was high were excluded.

The average relation between the composition of the soils and the effect
of the superphosphate on blackifinger grass is shown in Table 5. Averages
for the unfertilized soils show a close relation between active phosphoric
acid in the soil and yield and percentage of phosphoric acid in the grass
grown on them, but not between the total phosphoric acid in the soil and
the response. As the active phosphoric acid in the soil increased, the
yield of grass, percentage of phosphoric acid, and weight of phosphoric
acid in the crops from the unfertilized soils markedly increased, and the
increases due to superphosphate decreased. Although the yields and the
phosphoric acid in the crops from the unfertilized soils differed widely,
differences among the fertilized soils were much smaller. The addition
of phosphoric acid in the superphosphate had offset considerably the
differences in available phosphoric acid in the unfertilized soils. Total

phosphoric acid and basicity in the soils were of minor importance in

determining the response to superphosphate.

Effect of Phosphates on Different Species of Grasses

The effect of differences in species of grasses upon the response to
phosphates was studied by growing several species on two samples of
Lufkin fine sandy loam. In the first set, one-half of the phosphate was
mixed with soil 65031 at the start of the Work in April, 1942, and the
second half was broadcast on the pots in August. Plants of Dallis,
Georgia, and Johnson grasses were set out and seeds of 11 other species
were planted on April 29. In the second set, all of the phosphate was
mixed with soil 66401 at the start of the work in March, 1943, and seeds

of seven species were planted on March 10. Results secured in this ex»

periment are given in Table 6.

Yields on the soils Without phosphate averaged nearly the same (16.3
and 20.8 grams) on the two soils, but ranged from 7.8 to 26.4 grams on
soil 65031, and from 12.2 to 31.1 grams on soil 66401. The wide dif-
ferences indicate that some of the grasses were lower than others in
their capacity to utilize soil phosphates. With superphosphate, yield ranged
from 33.9 to 51.2 grams on soil 65031 and from 51.6 to 82.7 grams on soil
66401; average yields for the two soils were 40.5 grams and 75.2 grams,
respectively. The differences between the two soils may be due partly
to difference in season, including period of growth, partly to» differences
in the two soils, and partly to the difference in the method of application

Table 6. Eflect of superphosphate (200 mgm. P205) and rock' phosphate (400 mgm. P20a) on total yield of dry matter and phosphoric acid in
diflerent species of grasses

   

 

_ Weighted average percentage
Total yield of dry matter of phosphoric acid in Recovery of
dry matter phosphoric acid added
Kind of grass
None Super Rock None Super Rock Super Rock
gm- gm- " gm- % % % % %
Lufkin fine sandy loam 65031
Black finger grass . . . . . . . . . . . . . . . . . . . . . . . . . 7.8 39 .5 20.9 23 27 .23 43 4 7.7

hodes grass . . . . . . . . . . . . . . . . . . . . . .. ... 9.5 48.4 27.8 24 26 .21 50 5 8.5

Bermuda grass . . . . . . . . . . . .. 12.5 34.3 17.4 24 .24 .27 29.2 4.1

Yellow beard grass . . . . . . . . . . . . . 13.3 35.0 22.9 22 .29 .25 35.1 6.8

Johnson grass . . . . . . . . . . . . . . . . . . . . . . . . . . .. 13.5 36.3 26.4 23 .24 .21 24.1 6.0

Angleton grass . . . . . . . . . . . . . . . . . . . . . . . . . .. 16.0 33.9 21.0 21 24 .23 23.2 3.7

Curly mesquite grass. . . . . . . . . . . . . . . . . . . . . 16.7 34.6 22.5 21 .24 .22 24.7 3.8

Feather finger grass . . . . . . 18.0 45.6 28.5 20 .26 .23 41.6 7.3

Carpet grass . . . . . . . . . . .. 18.8 37.1 24.0 21 28 .26 32.1 6.0
Ribbed paspalum grass .. . 21.4 51.2 30.1 17 29 .23 55.0 8.2
Sideoats grama grass . . . . . . . . . . . . . . . . . . . . . . 21 .5 49.6 33.5 20 .21 .22 31.4 7.4
Georgia grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26.4 41 .2 30.1 2 28 .23 29.4 3.2
" Dallis grass* . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 8.5 17.5 12.2 22 .30 .27 34.2 7.0
\Veeping love grass* . . . . . . . . . . . . . . . . . . . . . . 10.1 18.7 14.2 23 .29 25 29.6 5.8
Lufkin fine sandy loam 66401
Sideoats grama grass . . . . . . . . . . . . . . . . . . . . . . 12.2 55.3 40.7 .17 23 .24 54 1 19.2

Buffalo grass . . . . . . . . . . . . . . . . . . . . . . . . . . .. 13.9 51.6 42.9 .19 27 .25 56 3 19.7

Black finger grass . . . . . . . . . . . . . . . . . . . . . . . . 20.7 68.0 38.9 .17 23 .23 60 8 13.1

Ribbed paspalum grass . . . . . . . . . . . . . . . . . . . . 20.9 80.8 71 6 .15 22 .19 71 9 25.7

Bermuda grass . . . . . . . . . . . . . . . . . . . . . . . . . .. 22.9 69.3 55 7 .18 23 .21 60 8 18.7

Yellow beard grass . . . . . . . . . . . . . . . . . . . . . .. 23.7 78.7 53.2 .14 20 .19 64 2 17.7

Rhodes grass . . . . . . . . . . . . . . . . . . . . . . . . . . .. 31.1 82.7 60.3 .14 19 .14 57 0 21.6

*Plants died before Aug. 4, when second one-half of phosphate was applied.

‘i ‘ ..
- ‘*.;~._._._.n.,-~.n . _,- .... .. .. ... . _... _. .. . .

f’!

NOLLVLS LNEIWIHEIJXC-I "IVHILUIIIOIHSV SVXELL ‘Z149 ‘ON NI-LEYITIIH

VALUE OF DIFFERENT PHOSPHATES FOR TEXAS SOILS AND GRASSES 15

of the phosphates. The higher yields were obtained on soil 66401, which
received all of the phosphate in a single application. Both superphosphate
and rock phosphate increased the percentage of phosphoric acid in the
grasses, but in no case up to 33% needed to prevent the grasses from
being deficient in phosphoric acid for range animals. The percentage of
phosphoric acid was usually higher with superphosphate than with rock
phosphate. The differences appear to be due chiefly to differences in
the ability of the plants to utilize soil phosphates. Superphosphate on soil
65031 increased the weighted average percentage of phosphoric acid by
more than 04% in ribbed paspalum, Dallis, yellow beard, carpet, Georgia,
feather finger, and weeping love grasses, and by .0270 or less in Rhodes,
Bermuda, sideoats grama, and Johnson grasses. Superphosphates on soil
66401 increased the percentage of phosphoric acid in all grasses, but the
increases were small in Rhodes and Bermuda grasses. Percentages were
lower and increases in percentage caused by superphosphate were greater
on soil 66401 than on soil 65031. '

The percentage of the added phosphoric acid recovered from super-
phosphate ranged from 23.2 to 55.0, average 35.0, with soil 66401, and
with soil 65031, from 54.1 to 71.9, average 60.7. Recovery from rock
phosphate was also higher on soil 66401 than on soil 65031. Recovery was
much greater when all of the phosphate was applied in one application
mixed with soil 66401 than in two applications carrying the same total

amount of phosphoric acid, half of which was mixed with soil 65031 and '

the other half broadcast later.

The high recovery in some grasses was due to large increases in yield,
and in other grasses, to smaller increases in yield plus considerable in-
creases in percentage of phosphoric acid. For example, superphosphate
increased the yield of Rhodes grass on 65031 from 9.5 to 48.4 grams but
increased the percentage of phosphoric acid only from 24% to 26%,
while the yield of ribbed paspalum grass was increased from 21.4 to 51.2
grams and the percentage of phosphoric acid from 17% to 29%. The
recovery of phosphoric acid was considerably higher in ribbed paspalum
than in any other grass. Results on both soils indicate that ribbed paspa-

lum is a heavy feeder on phosphoric acid in the soil; this is also shown .

by the large increase in yield of this species due to rock phosphate. Re-
coveries in black finger and Rhodes grasses were relatively high on both
soils. Recoveries in Bermuda and yellow beard grasses were high on
66401 but considerably lower on 65031. The average recovery by all
species was considerably higher on 66401 than on 65031; part of this dif-
ference is due to higher yields caused by the earlier date of planting
(March 10 as compared with April 29), and part to the fact that only
one-half of the phosphate had been added to 65031 throughout the early
part of the growing season.

Results of this experiment furnish information concerning several im-
portant practical points. Although superphosphate applied to these phos-
phorus-deficient soils greatly increased the total amount of phosphoric

91

*One-half of phosphate added to 65031 at start and one-half 0n Aug. 4. Recovery calculated from total quantity‘ added.
**All of phosphate added at start.

EU

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F‘

t4

ti

Table 7. Efiect of superphosphate (200 mgm. P205) and rock phosphate (400 mgm. P205) on yield and phosphoric acid in grasses at diflerent dates z
Z

9

Weighted average percentage of Recovery o_f _
Total yield of dry matter phosphoric acid in dry matter added phosphoric acid 3
Date of clipping 5°
_ None Super Rock None Super Rock Super Rock

sm- gm- gm- % % % 00 % Q

>4

Soil 650311‘ ti:

6/ 5/42 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1.7 7.7 3 2 .26 .27 29 7.9 1.2 _

6/24/42 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2.1 4.6 4 5 .22 .29 24 4.3 1.5 g

3/42 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4.5 8.2 6 6 .21 .26 23 5.7 1.5 a

9/16/42* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2.6 10.5 3 7 .23 .28 24 12.0 0.8

11/3/42 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4.2 10.2 as .20 .25 21 8.6 1.2 g

Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 15.1 41.2 24 3 .22 27 24 38.5 6.2 S
Soil 66401** g
5/26/43 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 0 12.3 5.0 25 .30 30 16.9 3.1 I>

6/30/43 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 5 4 16.1 12.0 15 .25 18 15.7 3.4 F‘

8/4/43 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3 9 13.3 11.4 17 24 22 12.5 4.5 t,’

9/15/43 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4 0 8.6 7.8 15 .22 19 6.3 2.1 >4

11/ 2/43 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 6.6 17.8 15.7 14 .16 18 9.3 4.8 g

Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 20.9 68.1 51 9 16 23 .20 60.7 17.9 a
S
P1
Z
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m
v-J
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O
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ll 

VALUE OF DIFFERENT PHOSPHATES FOR TEXAS SOILS AND GRASSES 17

acid in the clippings, the increase in some species was due almost entirely
to increases in yield, and in other species was due to a considerable in-
crease in both yield and‘ percentage of phosphoric acid. The botanical
composition of a pasture may influence to a considerable degree the nature
and degree of the response to applications of superphosphate. One large
application of superphosphate caused greater increases in both yield and
percentage of phosphoric acid than did two small applications carrying
the same total amount of phosphoric acid. The relative order of different
species of grasses in their response to superphosphate may differ con-
siderably on different soils.

Effect of Phosphates on Yield and Composition at Different Dates

The previous discussion was based on the total yields from 5 clippings

secured throughout the growing season. The results averaged according _

to date of clipping are presented in Table 7. Averages for soil 65031 were
calculated for only eight grasses of which clippings were secured at all
dates shown in Table 7; all grasses on soil 66401 were clipped at all dates.

Superphosphate greatly increased the yields at all dates. At the first
clipping, good yields were secured from superphosphate pots, but yields
from unfertilized pots were very small. The first clipping on unfertilized
pots represented about 10% of the total yield on soil 65031 and 5% on
soil 66401, compared with about 25% from superphosphate pots. At the
first clipping, increases due to superphosphate were several times those
due to rock phosphate. This is in agreement with the work of DeTurk
(14), who stated that phosphoric acid in superphosphate is available to
young seedlings but that in rock phosphate is not available. At later clip-
pings, differences between superphosphate, rock phosphate, and no phos-
phate were smaller. Following the broadcast application of the second
one-half of the phosphates to soil 65031, superphosphate again greatly in-
creased the yield, but rock phosphate had little effect. During the first
part of the growing season (April, May, June, July), the grasses on soil
66401 had twice as much phosphoric acid in superphosphate as those on
soil 65031, and this resulted in much greater relative increases in yield in
the first 3 clippings. The beneficial effect of the greater amount of
phosphoric acid available during the early part of the growing season
is also shown by the increases in total yield. Superphosphate increased
the average yield on soil 65031 by 2.7 times, and on soil 66401 by 3.3
times.

The average precentage of phosphoric acid in the first clipping was
not significantly increased by superphosphate on soil 65031, but was in-
creased on soil 66401. All of the phosphoric acid taken up by the young
plants from the smaller amount of phosphate on 65031 was used in pro-
ducing additional plant material, whereas, when twice the amount of
superphosphate was applied on soil 66401, the additional phosphoric acid
not only caused a much greater relative increase in yield of the young
plants, but also caused a significant increase in percentage of phosphoric

Table 8. Summary of percentage recovery of phosphoric acid added in superphosphate and rock phosphate
Mean percentage _ _ Coefficient of
Number recovered Standard deviation variation
Experiment of pairs
Super Rock Super Rock Super Rock
Different soils (32% rock)
Black finger grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11 30.8 3.3 11.0 as .35 1.09
Bermuda grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. l0 46.3 0.6 7.5 2.3 .16 3.93
Different grasses -
Soil 65031 (32% rock) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 14 31.4 6.1 12.9 3.1 .41 .51
Soil 66401 (34% rock) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 7 60.7 17.9 6.1 4.8 .10 .27
All experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . 42 39 .7 6.0 15.1 .4 .38 .73

SI

NOLLVLS LNEINIHHJXH TVHIIJTIIIOIHDV SVXELL ‘Z119 ‘ON NLLEYITQEI

VALUE OF DIFFERENT PHOSPHATES FOR TEXAS SOILS AND GRASSES 19

acid in the dry matter. The percentage of phosphoric acid in the grasses
was much lower in the later clippings than in the first one, and differences
in the percentage of phosphoric acid caused by the fertilizers were greater.
Recovery of phosphoric acid from superphosphate applied in one applica-
tion to soil 66401 decreased with each succeeding clipping except the last,
chiefly because of the decreases in yield. ‘

Recovery of Phosphoric Acid in Superphosphate Compared with
that in Rock Phosphate ~

Data secured in 42 paired comparisons made in this work are sum-
marized in Table 8. The average percentage of recovery of phosphoric
acid added in superphosphate in the different experiments ranged from
30.8 to 60.7, and in rock phosphate, from 0.6 to 17.9. Recovery of phos-
phoric acid in superphosphate applied to different soils and grasses varied
considerably, but the coefficient of variation for superphosphate was al-
ways much smaller than that for rock phosphate. A considerable per-
ceniage of the phosphoric acid added in superphosphate was recovered
in every comparison; none of that added in rock phosphate was recovered
on a number of the soils with Bermuda grass, and only small percentages of
the phosphoric acid added in rock phosphate were recovered in any com-
parison. The average recovery of phosphoric acid from one rock phos-
phate (17.8%) was about three times that recovered from another rock
phosphate (6.1%) on the same soil; companion averages for superphos-
phate were 60.7% and 31.4%. The averages given in Table 8 show that the
recovery of phosphoric acid from superphosphate was always several
times that from rock phosphate. <

Effect of Different Amounts of Phosphates on Yields and Composition
of Grasses

The phosphoric acid in superphosphate containing 200 mg. of phos-
phoric acid was used by the grasses for growth, if other conditions favored
it, with little increase in the percentage of phosphoric acid in the grass.
An experiment was also conducted in which different amounts of phos-
phoric acid in superphosphate (200, 400, 800, and 1,600 mgm.) and in
rock phosphate (800 and 3,200 mgm.) were added to Lufkin fine sandy
loam 66401. Each treatment was made in triplicate. Weighed amounts
of Bermuda and Rhodes grass seed were planted on March 22, 1944. From
this point, the procedure was the same is in previous experiments. Re-
sults secured are shown in Table 9.

The lowest amount of superphosphate (200 mg. phosphoric acid) greatly
increased the yields. The percentage of phosphoric acid in the dry matter
was increased in Rhodes grass, but was not increased in Bermuda grass.
As the amount of superphosphate increased, both yields and percentages
of phosphoric acid alsolincreased, but the relative effect upon yield de-
creased while that upon percentage of phosphoric acid increased. Phos-
phoric acid in the dry matter reached a maximum of .47% in Bermuda

20 BULLETIN N0. 672, TEXAS AGRICULTURAL EXPERIMENT STATION
Table 9. Efiect of different amounts of superphosphate and rock phosphate upon total yield
and phosphoric acid in Bermuda and Rhodes grasses
r _ Percentage of Recovery 0f
fotal yield of phosphoric acid phosphoric acid
dry matter in dry matter added
gm- % "70
Bermuda grass
No phosphate . . . . . . . . . . . . . . . . . .. 19.5 .18 . . . . . . . . . . . . . . ..
Superphosphate (200 mg. P205) . .. . 52.5 .18 47,5
§uperphosphate (400 mg. P205) . .. . 59.9 .21, 27_9
buperphosphate (800 mg. P205) . .. . 72. 8 .32 25.0
Superphosphate (1600 mg. P205)... 76.4 .47 22.5
Rock phosphate (800 mg. P205) . . .. 25. 0 . 18 1,2
Rock phosphate (3200 mg. P205).. . 33.3 18 0,8
Rhodes grass
No phosphate . . . . . . . . . . . . . . . . . . . 26.1 . 17 , , , _ _ , _ _ , _ _ _ v ‘ A _
Super-phosphate (200 mg. P205) . .. . 59 .4 .22 43 .2
Superphosphate (400 mg. P205) . .. . 81 .3 .24 38,6
Supcrphosphate (800 mg. P205) . .. . 91.9 .31 30, 7
Superphosphate (1600 mg. P205) . .. 95.0 .59 32,2
Rock phosphate (800 mg. P205) . . .. 32. 8 .17 1.6
Rock phosphate (3200 mg. P205).. . 35.2 .18 0.6

grass and .59% in Rhodes grass: Sufficient applications of superphosphate
increased the percentage of phosphoric acid appreciably above the minimum
percentage (0.33%) required for the adequate nutrition of range cattle.

Rock phosphate even in large amounts, increased yields much less than
did smaller amounts of superphosphate, and had almost no effect on the
percentage of phosphoric acid in the grasses. Rock phosphate is not a
suitable fertilizer for pasture land.

Value of Other Phosphates

In addition to superphosphate and rock phosphate used for the seven
grasses grown on Lufkin fine sandy loam 66401 (Table 6), several other
phosphates were used in order to estimate their relative value. Two
hundred milligrams of phosphoric acid were added in ammonium phos-
phate and in calcium metaphosphate; 400 milligrams of phosphoric acid
were added in finely ground rock phosphate (32% total P205), defluorinated
rock phosphate (29.8% total P205), and basic slag (13.46?) total P205).
Average results witheeach of these phosphates are compared with those
with superphosphate and rock phosphate to Table 10.

Results with ammonium phosphate and calcium _metaphosphate were
practically the same as those with superphosphate. Results with finely
ground rock phosphate and soft rock phosphate with colloidal clay Yvere
similar to those with ordinary rock phosphate. Defluorinated rock phos-
phate and basic slag caused increases in yield and percentage of phosphoric
acid considerably greater than those caused by superphosphate carrying
one-half as much phosphoric acid. The phosphoric acid in defluorinated
rock phosphate and basic slag was nearly as available as that in super-
phosphate and several times as available as that in the rock phosphate.
The phosphates used may thus be divided into two groups based upon the

 

 

 

VALUE OF DIFFERENT PHOSPHATES FOR TEXAS SOILS AND GRASSES 21

Table 10. Effect of different phosphates upon total yield and phosphoric
acid in 7 grasses

Percentage
Phosphoric Total yield Increase in of phos- Recovery of
acid of dry ‘ yield due to phoric acid phosphoric
added matter phosphate in dry acid
mgm. gm. gm. matter added
% %
No phosphate . . . . . . . . 0 20.9 . . . . . . . . . . . . .16 . . . . . . . . . . . .
Superphosphatc. . .. . . . 200 68 .1 47.2 .23 60.7
Ammonium phosphate. 200 70.3 49 .4 .22 60. 1
Calcium meta-
phosphate . . . . . . . . . . 200 68.7 47.8 .22 58.9
Rock phosphate. . . . .. 400 52.0 31.1 .19 16.9
Finely ground rock
phosphate . . . . . . . . . . 400 54.0 33.1 .20 19.5
Soft rock phosphate. . . 400 50.4 29.5 .21 17 .9
Defluorinated rock .
phosphatc.......... 400 83.9 63.0 .25 43.7
Basic slag............ 400 79.7 58.8 .26 43.8

Table ll. Effect of dicalcium phosphate (412 mgm. P205) upon total yield and phosphoric
acid in four grasses

Total yield of Percentage of
dry matter phosphoric acid Recovery of
in dry matter phosphoric
acid added
None Phosphate None Phosphate %
gm. gm. % %
Buffalo grass . . . . . . . . . . . . . . . .. 10.7 18.1 .30 .50 14.1
Little bluestem grass. . . .. . . . .. 22.8 24.0 .23 .44 12.3
Sideoats grama grass . . . . . . . . .. 24.7 33.9 .20 .37 18.3
Black finger grass . . . . . . . . . . .. 25.0 30.9 .29 .50 20.1

availability of their phosphoric acid. Phosphoric acid in superphosphate,
ammonium phosphate, calcium metaphosphatei, defiuorinated rock phosphate
and basic slag was highly available; that in ordinary rock phosphate, finely
ground rock phosphate, and soft rock phosphate with colloidal clay was
only slightly available even on this very favorable soil.

Dicalcium phosphate (1 gram of salt or 412 milligrams of phosphoric
acid) was used in one experiment with a Lufkin-fine sandy loam (49075,
Table 2) on four grasses. The results are shown in Table 11, principally
because they were considerably different from those secured on the other
two Lufkin fine sandy loams (65031 and 66401). Yields and percentages of
phosphoric acid in grasses grown on the unfertilized pots of this soil,
were very similar to those on the other two soils. On this soil, however,
dicalcium phosphate caused comparatively small increases in yield and
very large increases in the percentages of phosphoric acid in the dry
matter. This experiment again provides evidence indicating that, where
available phosphoric acid is added to a phosphorus-deficient soil under con-
dition.s where the increases in yield are relatively small, the additional
phosphoric acid will be used by the plant to increase the percentage of
phosphoric acid in the dry matter.

22 BULLETIN NO. 672, TEXAS AGRICULTURAL EXPERIMENT STATION

x. A‘ _,. 4.1L

DISCUSSION

While results of pot experiments in the greenhouse are not directly ap-
plicable to field work, they do give valuable information concerning cer-
tain general relations which are applicable. A due appraisal of the results
secured in pot experiments is thus of practical value.

Superphosphate: The addition of a limited amount of superphosphate
to soils which were deficient in active phosphoric acid resulted in very large
increases in yields of dry matter. Where the application of superphos-
phate did not produce large increases in yield, the added phosphoric acid
Was used by the plants to increase the percentage of phosphoric acid in
the dry matter. Where larger amounts of superphosphate were applied,
theadditional phosphoric acid was used to produce some additional dry
matter, but most of it was used to raise the percentage of phosphoric acid
in the dry matter. The phosphoric acid in superphosphate is used primarily
to increase the yield of dry matter, and secondarily, to increase the per-
centage of phosphoric acid in the dry matter. Since percentage of phos-
phoric acid, rather than yield, is the principal factor in satisfactory animal
production on many Texas pastures, the amount of superphosphate to
be added should be sufficient not only to raise the yield to a satisfactory
level, but also to raise the percentage of phosphoric acid in the dry mat-
ter to a level higher than the minimum requirements for range animals.
The amount to be applied will also be influenced by the amount of active
phosphoric acid in the unfertilized soil, and by the capacity of the soil
to fix phosphoric acid in unavailable or slowly available compounds.

A single large application of superphosphate appears to be better than
two small applications carrying the same amount of phosphoric acid.
Superphosphate should be added at a time when the additional phosphoric
acid will be available to stimulate the growth of seedlings and develop
them into strong plants before the advancing season brings unfavorable
growth conditions.

Superphosphate greatly increased bloom and seed production in nearly
all species of grass. The stimulation of seed production following the
application of superphosphate may be of practical importance, particularly
on many of our over-grazed or depleted ranges. Superphosphate resulted
in very greatly increased root systems; under range conditions this would
be of value in increasing the capacity of the plant to secure food and
water. Superphosphate considerably reduced the loss of seeedlings due
_to “damping off”.

Rock phosphate: The availability of phosphoric acid in rock phosphate
is much lower than in superphosphate. Rock phosphate significantly in-
creased yields of black finger grass on only 4 out of 14 soils and on 5 out
of 15 species of grass grown on a favorable soil. It increased the per-
centage of phosphoric acid in the grasses in only a few cases. Rock phos-
phate did not cause much increase in either yield or percentage of phos-
phoric acid in young grasses. Increasing the amount of rock phosphate

 

VALUE OF DIFFERENT PHOSPHATES FOR TEXAS SOILS AND GRASSES 23

§§or the period of contact with the soil did not result in any further in-
 crease. In all cases where increases due to rock phosphate were secured,
they were much smaller than those produced by superphosphate carrying
only half as much phosphoric acid. Rock phosphate cannot be recom-

 range grasses.

E ACKNOWLEDGEMENT
E
P
E

_ Chemical analyses and other work was done by Mr. T. L. Ogier, Waldo
 Walker, and other members of the staff.

SUMMARY

p Yields of black finger grass and Bermuda grass grown in pot experi-
 ments without phosphate varied widely according to the soil, chiefly due
' to differences in the active phosphoric acid content of the soils. When
‘superphosphate was added, the yields were more nearly uniform. The
’ effect 0f the superphosphate depended on the soil, being greater where the
Qsoil was more deficient in active phosphoric acid. The application of
p limited amounts of superphosphate increased the yield to a greater extent
than it increased the percentage of phosphoric acid in the grasses.

The yield and percentage of phosphoric acid in the grasses was closely
related to the amount of active phosphoric acid in the soils.

When 14 species of grasses were grown on the same unphosphated soil,

' considerable differences occurred among the yields of grass. When super-

phosphate was added, the differences were much smaller. This indicates

that the differences were chiefly due to differences in the capacity of the
grasses to utilize soil phosphates.

One application of superphosphate at the beginning of the season pro-
duced larger yields with greater increases in percentage of phosphoric
acid than the same amount of phosphoric acid added in two applications.
Small applications of superphosphate usually produced large increases in
yield but small increases in the percentage of phosphoric acid in the
grasses. As the quantity of superphosphate was increased, the effect on
the yield was less but the effect on the percentage of phosphoric acid in
the grasses was greater. Liberal applications of superphosphate pro-
duced large yields of dry matter containing good percentages of phos-
phoric acid.

Superphosphate stimulated early growth and seed formation.

Applications of ground rock phosphate increased yields in a few cases,
but the increases were not nearly as great as those for superphosphate.
Ground rock phosphate, even when applied in large quantities, usually
had little effect upon the percentage of phosphoric acid in the grasses.

Phosphoric acid in ammonium phosphate, calcium metaphosphate, de-
fluorinated rock phosphate, and basic slag applied to a slightly acid,

24

phosphorus-deficient Lufkin fine sandy 10am was nearly as available >

that in 20%
‘rock phosphate or in soft rock phosphate with colloidal clay was no mo -
available than that in ordinary ground rock phosphate.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

BULLETIN NO. 672, TEXAS AGRICULTURAL EXPERIMENT STATION

   
  
   
   
  
   
   
   
  
   
  
    
  
  

superphosphate. Phosphoric acid added in finely u.

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Official and tentative methofifi

chemical composition
5.

Phosphorus deficiency 
possibility of  i 

Fraps,
phate.

Chemical composition of soils of Texas. '1‘

25.

26.

27.

‘ 2s.

29.

30.

31.

32.

33.

34.

as.

36.

37.

38.

39.

40.

41.
42.

' 4s.

A 44.

45.

l;- 4s.

 41.

 

I

VALUE OF DIFFERENT PHOSPHATES FOR TEXAS SOILS AND GRASSES 25

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