E155

   

BULLETIN

EXAS AGRICULTURAL EXPERIMENT STAT|ON/ J. E. Miller, Director/ Texas A&M University/ College Station, Texas

m

B-1151
May 1975

ECONOMIC OPTIMUM RATES AND RETURNS FROM NITROGEN F ERTILIZATION
OF COASTAL BERMUDAGRASS FOR HAY IN EAST TEXAS l

J. E. Matocha*

SUMMARY

The price of nitrogen has risen considerably recently, and
producers need to figure the most economic nitrogen rates
for their own situation. Knowledge of the nature of
response by Coastal bermudagrass to various rates and forms
of nitrogen can be helpful in the close calculation of the
most profitable rate of nitrogen fertilization.

Research comparing production of Coastal bermudagrass
forage from different rates and five forms of nitrogen
fertilizer began in 1969 at the Texas A&M University
Agricultural Research and Extension Center at Overton.

The 5-year study compared urea, ammonium nitrate,
ammonium sulfate and two nitrogen experimental con-
trolled-release materials (sulfur-coated ureas) on a rela-
tively deep, sandy soil. The long-term experiment included
two seasons when rainfall in East Texas was considerably
below normal. However, data from all 5 years were used
in making the economic evaluations. Nitrogen was the
only variable in the research with phosphorus, potassium
and sulfur applied according to soil test. Three split
applications of nitrogen were used in the initial year while

five applications were made in all other years withi

the exception of 1973 (four applications). The first applica-
tion was made about April l. Potassium was split,
while -=all phosphorus and sulfur was added with the initial
application of nitrogen.

By use of a computer, single variable production functions
for each of the sources of; nitrogen studied were developed,
utilizing the 5 years of production data from the field.

*Associate professor, The Texas Agricultural Experiment Station,
Overton.

NITROGEN RESPONSE

During the research period, forage production was variable

among years. For example, with below normal rainfall in

the summer of 1969 and 200 pounds of nitrogen applied
per acre, Coastal bermudagrass produced 32 pounds of
forage per pound of nitrogen, while in 1973, with adequate
rainfall, 76 pounds of forage per pound of nitrogen were
produced.

The research has shown that Coastal bermudagrass is
generally highly responsive to nitrogen fertilization. The
nitrogen response curve follows a near-linear pattern at
rates of less than 200 pounds per acre but will assume a
quadratic nature at higher rates. How fast the production
efficiency from nitrogen drops with rate depends on many
factors, one of which is rainfall. The most efficient pro-
duction (pound forage per pound nitrogen) is usually found
at the front portion of the nitrogen response curve,
synonymous with the largest net return per dollar invested
in nitrogen fertilizer. However, whether bermudagrass
needs to be fertilized at the rate needed to be at this

portion of the curve will depend primarily upon two "

factors: (l) the amount of hay needed and the number of
acres of Coastal bermudagrass meadow available and (2) the
protein level desired in the forage. Protein will not reach
the choice l2-percent level unless at least 6O pounds of
nitrogen per acre is applied following each cutting of hay.

OPTIMUM RATE

Economic optimum rates of nitrogen fertilization were
developed using the production functions. Since ammo-
nium nitrate and urea are the most common sources of
nitrogen fertilizer in the East Texas region, economic

optimum rates and returns are presented for these two
materials. Similar data for ammonium sulfate and experi-
mental sulfur-coated ureas will be available but are not
presented here.

In obtaining these calculations, costs of other essential
fertilizer nutrients, such as phosphorus, potassium and
sulfur, were included as well as harvesting costs. An average
harvesting cost of 55 cents per bale (40 cents for baling and
15 cents for hauling) for 55-pound bales was subtracted
from the selling price of the hay prior to calculation of the
optimum economic rates. Other fixed costs, such as weed
control, interest on capital and others that comprise a
small fraction of the total expense, have not been included
in these calculations.

Table 1 shows various nitrogen fertilizer rates and prices,
as they relate to hay costs. For example, with urea at
$225 per ton, or 25 cents per pound of nitrogen, and hay
valued at $50 per ton, the optimum economic rate of
fertilization would be 340 pounds of nitrogen per acre,
which would provide a return of $1.61 for each dollar
invested in fertilizer. In this example the total profit from
fertilizer is $51.85 per acre.

Using ammonium nitrate at the same price per pound of
nitrogen (25 cents or $168 per ton) and $50 per ton for
hay, the optimum nitrogen rate is 357 pounds per acre,
with a total profit of $70.50 per acre from fertilizer)

NITROGEN SOURCE DIFFERENCE

The difference in profit per acre attributable to nitrogen
source is primarily a result of forage production differences.
The 340 pounds of nitrogen per acre yielded 6.75 tons of
forage when applied as urea and 7.25 tons when ammonium

lExample formula for figuring profit per acre:
lb. N per acre X cost per lb. N X dollar return per dollar
fertilizer = profit per acre
For $225 per ton urea and $50 per tonhay:
X ($1.61 — $1.00) = $51.85
For $168 per ton ammonium nitrate and $50 per ton hay:
357 X .25 X ($1.79 — $1.00) = $70.50

340 X .25

nitrate was used. Protein content of the forage at this rat
averaged approximately 13 percent for the five cuttings t.

hay.

If the price of hay is increased by $10 per ton (to $60 p

ton), the optimum economic rate__of nitrogen increases t)
475 and 468 pounds per acre, respectively, for urea an‘
ammonium nitrate. Likewise, the returns per dollar invest i;

in fertilizer increases significantly over 25 cents.

Differences in the optimum rate of nitrogen and refur‘

due to nitrogen source appear to widen slightly as“ h‘
prices increase. A

OTHER FACTORS

Harvesting costs of hay are a major factor in the net val A
of the hay and, consequently, play a large role in the co ‘
puted economic optimum rates of nitrogen fertilizatio
If harvesting equipment is owned or readily availabl
these costs then may be reduced and the nitrogen rat
for economic production of Coastal bermudagrass w'
increase. On the other hand, if harvesting costs l‘

higher than the calculated cost of $19.80 per ton of ha .
the nitrogen rates and fertilizer returns are over-estimate ‘

‘One of the most important factors determining the nitroge“

fertilization rate is the expected selling price of the ha ~1
Although it may be difficult to predict hay prices sever
months in advance, it is important to establish som
estimated selling price to determine an economic rate f r
optimum nitrogen fertilization. A differential hay pric:
of $10 per ton, or slightly more than 25 cents per bal
xvill have a substantial effect on the amount of nitroge‘
fertilizer that is profitable to use. For example, it ca
mean the difference between not being able to fertiliz
the hay meadow profitably ($30 per ton of hay) an
fertilizing for some profit ($40 per ton of hay).

Mention of a trademark or a proprietary product does n
constitute a guarantee or a warranty of the product by The Tex
Agricultural Experiment Station and does not imply its approv
to the exclusion of other products that also may be suitabl

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The Texas Agricultural Experiment Station, J. E. Miller, Director, College Station, Texas
1.5M—5-75