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"M713 April 1995

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JUN 13 1995 j
TEXAS STATE

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Texas Agricultural Experiment Station ' Edward A. Hiler, Director" Tile Texas AfdM University System ' College Station, Texas

 

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Dryland Wheat Response to
Nitrogen and Phosphorus Fertilization

Betty A. Kramp and David Bordovsky‘

Summary

Growth characteristics and grain yield response
of dryland wheat were compared between four levels
of nitrogen (N) and four levels of phosphorus (P) fer-
tilization. No plant responses to P fertilizer addi-
tions or t0 N-P combinations were observed, and N
fertilization alone did not inﬂuence grain yields. N
fertilizer levels of 0 and 20 lbs/A resulted in a 1 lb/bu
higher test weight than did the 40-80 lbs N/A levels.
Annual additions of fertilizer N did not result in in-
creased soil proﬁle N. With each successive crop, soil
proﬁle nitrates were reduced even with the annual
addition of 80 lbs N/A. The 40 and 80 lbs N/A rates
slowed soil proﬁle nitrate depletion rate.

Introduction

Grower experiences generally dictate rates of N
and P fertilizer on dryland wheat in the Texas Roll-
ing Plains. Soil test recommendations have been
largely developed by calibration studies outside the
region. There are few published reports on effects of
fertilizer N or P on dryland wheat in the Rolling
Plains. Unpublished observations suggest that fer-
tilizer increases grain yield of dryland wheat in some
but not all sites and/or situations. The objective of
this study was to examine the effects of N and P fer-
tilizer on the grain yield of dryland wheat and to de-
termine the effect of N fertilization on residual soil
nitrate levels.

Methods and Materials

Fertilizer plots were established on a Miles ﬁne
sandy loam soil (Udic Paleustalf), during October
of 1990 at the Texas Agricultural Experiment Sta-

‘Respectively, research associate and research scientist at
Texas A&M University Vegetable Research Station,
Munday, Texas.

tion experimental farm near Munday, in Knox
County, Texas. Knox County is located on the
Seymour Aquifer. The Seymour Aquifer is charac-
terized by shallow depth to water with the major-
ity of wells drilled to a depth of only 29 to 69 feet.
The Seymour Aquifer also contains a large amount
of NOB-N with individual wells ranging from 21-
139 ppm (Wendt et al., 1976).

Each plot was 26.6 feet wide by 50 feet long. Dry
granular N and P fertilizers were broadcast preplant
and incorporated immediately with a disk to a depth
of 6 inches at 0, 20, 40, 80 lbs and 0, 15, 30, 60 lbs
respectively. N was applied as ammonium nitrate
and P applied as triple super phosphate on October
29, 1990 and in early September in 1991 and 1992.
In 1992 the N was applied in a split application with
one-half broadcast preplant and incorporated, and
one-half broadcast as a top dressing prior to jointing
in early March 1993. All fertilizer applications were
made using a four row spreader. Plots were main-
tained in the same location each year so that cumu-
lative treatment effect could be examined.

Hard red winter wheat cultivar TAM W-101 (Por-
ter, 1974) was planted on October 31, 1990. Due to
unavailability and lack of popular use TAM W-101
was replaced by TAM W-200 (Worrall, 1994) in 1991
and 1992 and was seeded on October 15 and Novem-
ber 3, respectively. Seeding rate was 60 lbs/A, a com-
mon seeding rate in Knox County. A plot combine
was used to harvest yield samples. The harvested
area consisted of a single 51 inch swath 50 feet long.
Measured plant response variables were plant height,
grain yield, and grain test weight. Plant height was
determined on an average of 10 plants/plot measured
at harvest.

A baseline soil sample was taken in each plot in
the fall of 1990. Soils were sampled again each year
of the study after harvest. Single soil cores were
taken at the approximate center of each plot at depths
0-6, 6-12, 12-24 and 24-36 inches. Samples were
placed in paper bags and dried in a forced draft oven

for 24 hours at 80° F. Dried samples were pulverized
in a hammer mill, passed through a standard num-
ber 10 soil sieve and a sub-sample analyzed for
NOs-N using the Phenoldisulfonic Acid Method
(Jackson, 1958; Dahnke and Vasey, 1973).

Tillage operations between crops were kept to
the minimum required to control weeds and for
land preparation only. Chlorsulfuron (2-Chloro-N-
[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]
carbonyl]Benzenesulfonamide, or Glean herbicide
was applied in February 1991 at .33 oz/A to con-
trol annual broadleaf weeds.

The study design was a randomized complete
block with four replications per treatment. Soil and
yield variables were analyzed in a two factor facto-
rial with nitrogen and phosphorus rates as the fac-
tors. Treatment means were compared with Least
Signiﬁcant Difference tests at the .05 probability level
(Steele and Torrie, 1960; Freed et al., 1985).

Results

No differences in grain yield, plant height, or seed
test weights were detected among P applications or
among any N-P combinations. Baseline soil phos-
phorus data is presented in Table 1. In addition no
signiﬁcant differences in grain yield or plant height
among any of the N treatments were observed (Table
2). There was a trend toward a negative response for

TABLE 1. Residual Soil Profile Phosphorus, Dryland Wheat
Fertilization Study, September 1990, Knox County, Texas.

Depth of Soil Sample

Phosphorus Treatment 0-6" 6-12" 12-24" 24-36"
lbs/A ppm P ppm P ppm P ppm P

0 33.5 13.0 ' 7.3 5.4

15 34.4 11.1 8.0 6.0

30 36.5 13.3 7.3 5.4

60 35.1 12.8 7.3 5.0

Average 34.9 12.6 7.5 5.5

grain yield to increasing N levels during all three
years of the study, but these differences were not sta-
tistically different (a=0.05). The 0 lbs N/A averaged

6 percent more grain than the 80 lbs N/A plots in 1991, ‘

26 percent more in 1992 and 10 percent more in 1993.
The three-year grain yield average for the 0 N plots
was 42.4 bu/A contrasted to 40.5, 38.8 and 38.4 in 20,
40 and 80 lbs N respectively. A 1 lb/bu higher test
weight was obtained for the 0 and the 20 lb N/A treat-
ments as compared to the 40 and 80 lbs N/A treat-
ments. None of the treatments inﬂuenced plant
height.

All treatment yields in 1992 were 40 percent be-
low the three-year average for the study. Excellent
growing conditions in 1992-93 with above average
rainfall throughout the crop season resulted in above
average grain yields across all the treatments and
for most dryland wheat planted in Knox County in
1993. Mild winters were experienced throughout the
three-year study period, and insect pressure and dis-
ease were not signiﬁcant factors during the study.

Baseline residual soil nitrate levels averaged 16.4
ppm at 0-6 inches, 18.0 ppm at 6- 12 inches, 11.6 ppm
at 12-24 inches, and 6.3 ppm at 24-36 inches in the
soil proﬁle. High soil nitrates within test plots in the
fall of 1990 reﬂect past use of this land which was in
highly fertilized vegetable production. Soil nitrate
levels were signiﬁcantly reduced at all depths and in
all fertility treatments after one crop year (Table 3).
Rate of soil nitrate reduction decreased with increas-
ing amount of N fertilizer. From September 1990 to
July 1991, soil nitrogen declined 67 percent in the
surface foot of the check treatment plots. Plots re-
ceiving 80 lbs N/A lost 57 percent of the residual soil
nitrogen during the 1990-91 crop season. Depletion
of soil nitrogen continued at approximately the same
rate from July 1991 to July 1992 as in the previous
year. Check plot residual soil nitrate in the surface
foot was reduced 47 percent while the 80 lbs N/A treat-
ment residual soil nitrate was reduced 27 percent.
Residual soil nitrate in the 12-24 and the 24-36 inch
depths of the 40 and the 80 lbs N/A treatments did

TABLE 2. Plant Height, Test Weight, and Yield of Dryland Wheat As Affected by Rates of Nitrogen Application in 1991, 1992, and 1993,

Knox County, Texas.

Mature Height, Inches Test Weight, lbs/bu Weld, bu/A
Nitrogen Rate 1991 1993 1991 1992 1993 1991 1992 1993 Avg.
0 19.7 31 64 51 61 41.3 27.5 58.5 42.4
20 20.1 31 63 51 61 38.4 26.2 57.0 40.5
40 19.7 31.5 63 5O 60 39.9 25.2 54.2 39.8
80 19.7 31 63 50 60 39.1 21.8 54.4 38.4
Average 19.8 31 .3 63 51 61 40 25 56
LSD.05a N.S. N.S. N.S. 1.4 1.2 N.S. 6.1 6.5

TABLE 3. Residual Soil Profile N03-N PPM 1990-1993, Dryland
Wheat Fertilization Study, Knox County, Texas.

Sample Date
Nitrogen Treatment September July July June
lbs/A 1990 1991 1992 1993
0-6" Depth

0 18.1 7.4 4.4 1.0

20 19.5 8.6 3.8 1.3
40 12.7 7.4 4.4 1.5
80 15.3 7.4 6.6 1.6
Average 16.4 7.7 4.8 1.4

6-12" Depth

0 17.8 4.9 2.1 1.5

20 19.4 5.1 1.9 1.5
40 19.8 4.3 2.1 1.5
80 15.2 5.4 2.7 2.6
Average 18.0 4.9 2.2 1.8

12-24" Depth

O 12.5 2.0 1.5 1.4

20 9.0 1.9 1.4 1.5
40 12.1 1.8 1.8 1.4
80 13.1 1.9 2.3 2.5
Average 11.6 1.9 1.8 1.7

24-36" Depth

0 7.8 2.5 1.9 1.5

20 5.3 1.6 1.5 1.3
40 5.8 1.5 1.6 1.3
80 6.4 1.6 1.9 2.2
Average 6.3 1.8 1.7 1.6

not change during the second crop year. Soil nitrate
levels at all depths declined to below 10 ppm after
two wheat crops. Soil analysis in June 1993 revealed
a continued decline in nitrate N in the surface foot of
the soil proﬁle.

The lack of grain yield response to fertilizer N
might be explained by below normal or sporadic
precipitation. In 1991, precipitation was 4 percent
below normal for the crop season; however, the
rainfall for the critical months of February-April
was 84 percent below normal. Precipitation was
above normal throughout the 1992 and 1993 grow-
ing seasons. Except for 1991, precipitation did not
appear to be a primary factor inﬂuencing lack of
response to fertilization. Below average grain
yields in 1992 may have been the result of exces-
sive rainfall in December of 1991.

There is little question that fertilization improves
yield of irrigated wheat. Pope (1963) found in the
Texas High Plains on Amarillo and Dalhart ﬁne sandy
loam soils that N and P alone did not affect yield of

irrigated wheat, but 8O lbs N/A in combination with
either 40 or 80 lbs P/A stimulated grain production,
and yields averaged 60-64 bu/A. No differences in
grain yield were reported for preplant vs. split appli-
cations of nitrogen or for ammoniacal vs. nitrate for-
mulations. Clark and Onken (1989) found N fertil-
izer increased irrigated wheat grain yields by 20-30
percent in two of three years on an Abilene clay loam
near Chillicothe, Texas. No yield responses to addi-
tions of P fertilizer or to combinations of N and P
were observed in this study. The 80 lbs N/A rate pro-
duced the highest yields of 58 and 85 bu/A in 1987
and 1988, respectively. N fertilizer above 80 lbs N/A
did not improve yields. However, no differences were
reported among any of the treatments in 1986.

Doyle and Holford, 1993 examined the results of
53 dryland fertilizer experiments on wheat in New
South Wales and Southern Australia, where a small
and infrequent response to fertilizer N was reported.
They found that increasing increments of fertilizer N
resulted in decreased N use efficiency (i.e., kg grain/
kg N applied). However, the highest rate of N fertil-
izer resulted in the greatest physiological efficiency
(grain protein/Kg N) which was sufficient to make
the highest fertilizer additions proﬁtable.

In studies where the N content of the forage
and grain were examined and compared to residual
soil N 03 from O-36 inches, Doyle and Holford (1993)
found that there was uptake of soil N above ap-
parent available levels. In these cases, it was dis-
covered that subsoil NOs-N was elevated by fallow
season rainfall leeching surface N Oa-N . Wheat was
apparently recovering N from levels below 3 feet
in the soil proﬁle.

Shallow water table and high levels of N03 in
water may be factors which have inﬂuenced the re-
sults of our study. Average depth to water in Knox
County is 23 feet with individual wells ranging from
4 to 55 feet (Harden et al., 1978). Irrigation water
samples taken from the TAES farm at Munday dur-
ing the study period averaged 20 ppm NOs-N.

Hough and Kolp (1978) reported disparate re-
sponse to fertilizer N applications on dryland winter
wheat among six locations in Wyoming. At one loca-
tion grain yields consistently decreased with in-
creased N applications regardless of application time;
fall preplant vs. spring top-dress. At four locations
fall preplant applications failed to improve yields.
This study also reported a decrease in grain test
weight with increase in N fertilization. Precipitation
at these locations was 5O percent of that normally
received in the Texas Rolling Plains.

Conclusions

While Clark and Onken (1989) reported an in-
crease in yield of irrigated wheat at Chillicothe,
Stephens (1962) reported that nitrogen fertilization
of dryland wheat at Chillicothe failed to enhance
yield. Our results concur with Stephens and suggest
that annual fertilizer nitrogen applications on Miles
soils in Knox County may not be necessary to increase
grain yield, especially where shallow water tables,
high in nitrates are found. Additions of nitrogen did
reduce the rate of nitrogen loss from the upper soil
proﬁle when compared to the control, but soil N 03-N
did not reach a steady state in three consecutive crops,
even at the 80 lbs N/A rate.

References

Clark, L. E., and A. Onken. 1989. Fertility-Soil Test
Correlation Study: Response of Wheat to Nitrogen
and Phosphorus. In: Soil Test/Plant Tissue Corre-
lation Project Final Report. H. J. Woodard et al.,
eds. Dept. Soil and Crop Sciences, Texas A&M Uni-
versity. College Station.

Dahnke, W.C., and E.H. Vasey. 1973. Testing soil for
Nitrogen. In: Soil Testing and Plant Analysis. L. M.
Walsh and J. D. Beaton, eds. Soil Science Society of
America. Madison.

Doyle, A. D., and E. C. R. Holford. 1993. The Uptake of
Nitrogen by Wheat, Its Agronomic Efficiency and
Their Relationship to Soil and Fertilizer Nitrogen.
Aust. J. Agric. Res. 44, 1245-58.

Freed, R., S. P. Eisensmith, S. Goetz, D. Reicosky, V. W.
Smail, and P. Wolberg. 1985. MSTAT Version 4.0
Software Program. Michigan State University.

Harden, R.W. and Assoc. 1978. The Seymour Aquifer
Ground Water Quality and avalibility in Haskell and
Knox Counties, Texas. Texas Department of Water
Resources Report 226. Vol. 1.

Hergert, G.W. 1987. Status of Residual Nitrate-Nitro-
gen Soil Tests in the United States of America. In:
Soil Testing: Sampling, Correlation, Calibration, and
Interpretation. J.R Brown, ed. SSSA Special Publi-
cation No. 21.

Hough, H. W., and B. J. Kolp. 1978. Dryland Wheat Fer-
tilization Trials in Wyoming, A Preliminary Report.
Research Journal 128. University of Wyoming.

Jackson, M. L. 1958. Soil Chemical Analysis. Prentice
Hall Inc.

Pope, A. 1963. Fertilizing Irrigated Wheat on the High
Plains of Texas, Texas Agricultural Experiment Sta-
tion. MP-688.

Porter, K. B. 1974. Registration of TAM W-101 Wheat.
Reg. No. 541. Crop Sci. Vol. 14, No. 4, 608.

Onken, A. B., R. Matheson, and E. J. Williams. 1980.
Evaluation of EDTA-extractable Phosphorus as a
Soil Test Procedure. Soil Sci. Soc. Amer. J. Vol. 44,
No.4., 783-786.

Steel, R.G.D., and J. H. Torrie. 1960. Principles and Pro-
cedures of Statistics. McGraw Hill Inc.

Stephen, J .C. 1962. Agricultural Research in Texas Sub-
station N o. 12. Texas Agricultural Progress. Vol. 8,
No. 5.

Wendt, C.W., A.B. Onken, and O.C. Wilke, 1976. Effects
of Irrigation Methods on Groundwater Pollution by
Nitrates and Other Solutes. EPA-600/2-76-291

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