Directory UMM :Data Elmu:jurnal:A:Agronomy Journal:Vol93.Issue1.2001:
HOWARD ET AL.: N FERTILIZATION OF NO-TILL COTTON
Soltanpour, P.N., G.W. Johnson, S.M. Workman, J. B. Jones Jr., and
R.O. Miller. 1996. Inductively coupled plasma emission spectrometry and inductively coupled plasma-mass-spectroscopy. p. 91–140.
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Wells, B.R. 1980. Zinc nutrition of rice growing on Arkansas soils.
Ark. Agric. Exp. Stn Bull. 848. Univ. of Arkansas, Fayetteville, AR.
Yilmaz, A., H. Ekiz, B. Torun, I. Gultekin, S. Karanlik, S.A. Bagci,
and I. Cakmak. 1997. Effect of different zinc application methods
on grain yield and zinc concentration in wheat cultivars grown on
zinc-deficient calcareous soils. J. Plant Nutr. 20:461–471.
Nitrogen Fertilization of No-Till Cotton on Loess-Derived Soils
Donald D. Howard,* C. Owen Gwathmey, Michael E. Essington, Roland K. Roberts, and Mike D. Mullen
ABSTRACT
Information on nitrogen (N) fertilization of no-till (NT) cotton
(Gossypium hirsutum L.) is needed to optimize lint yields and earliness. We evaluated five N rates and three application methods for
NT cotton production on Loring silt loam (fine-silty, mixed, active,
thermic Oxyaquic Fragiudalfs) with natural winter annuals as a cover;
and on Memphis silt loam (fine-silty, mixed, active, thermic Typic
Hapludalfs) having corn (Zea mays L.) stover as a cover and on
Lexington silt loam (fine-silty, mixed, active, thermic Utlic Hapludalfs)
having winter wheat (Triticum aestivum L.) as a cover. Nitrogen rates
of 0, 34, 67, 101, and 134 kg ha21 were either broadcasted as ammonium nitrate (AN) or injected as urea–ammonium nitrate (UAN) at
planting. Additional treatments included broadcasting 67 kg N ha21
as AN at planting with either 34 or 67 kg N ha21 banded 6 wk later.
Relative to no N, broadcasting 67 kg N ha21 as AN increased 4-yr
average NT lint yields on Loring silt loam from 739 to 1281 kg lint
ha21 and 2-yr average yields on Lexington silt loam from 1086 to 1535
kg ha21. A higher N rate (101 kg N ha21) was needed to increase 2yr average yields on Memphis silt loam from 821 to 1169 kg ha21.
Broadcasting AN was a satisfactory placement method producing
yields equal to or higher than injecting UAN or splitting AN for
NT cotton produced on these loessial soils despite different covers
and residues.
N
itrogen (N) fertilization affects yield, maturity, and
lint quality of cotton. Evaluating N rates, sources,
and application timing for optimum lint production has
been a major research emphasis within the cotton producing states. For cotton, applying an optimum N rate
is essential and may differ within the production areas
due to climatic or soil differences. An optimum N rate
should maximize yields, while excessive or inadequate
N applications may reduce cotton yields (Maples and
Keogh, 1971). High N fertilization may produce excessive vegetation that delays maturity and harvest, and
these conditions may reduce yields and lint quality during years of early frost or prolonged fall rain (Hutchinson et al., 1995; McConnell et al., 1995). Crop maturity is
a critical production consideration for cotton producers
along the northern edge of the U.S. Cotton Belt (Gwathmey and Howard, 1998). Nitrogen deficiency causes preD.D. Howard and C.O. Gwathmey, Plant and Soil Sciences Dep.,
Univ. of Tennessee, West Tennessee Exp. Stn., Jackson, TN 38301;
M.E. Essington and M.D. Mullen, Plant and Soil Sciences Dep., Univ.
of Tennessee, P.O. Box 1071, Knoxville, TN 37901-1071; and R.K.
Roberts, Agric. Economics and Rural Sociology Dep., Univ. of Tennessee, P.O. Box 1071, Knoxville, TN 37901-1071. Received 26 Jan.
2000. *Corresponding author (dhoward2@utk.edu).
Published in Agron. J. 93:157–163 (2001).
mature senescence and reduced yields (McConnell et
al., 1995).
Research conducted within the mid-South shows that
the optimum N rate for cotton production varies with
location, soil type, tillage system, winter cover, and application method. On conventionally tilled (CT) Dundee very fine sandy loam (fine-silty, mixed, active, thermic Typic Endoaqualfs), Ebelhar and Welch (1996)
reported optimum yields from banding 50% of the N
at planting followed by banding 50% at pinhead square.
Their evaluation included N rates (67–168 kg ha21) and
application timing (at planting and three splits) from
which they concluded that the 50–50 split application
of 101 kg N ha21 resulted in the highest yields. In an
additional study, Ebelhar et al. (1996) showed that injecting a 50–50 split (at planting and pinhead) at a higher
rate (134 kg N ha21) resulted in maximum cotton yields
on CT Bosket very fine sandy loam (fine-silty, mixed,
active, thermic Typic Hapludalfs) and Dubbs silt loam
(fine-silty, mixed, active, thermic Typic Hapludalfs). In
Mississippi, Thompson and Varco (1996) reported that
broadcasting 121 kg N ha21 as ammonium nitrate (AN)
and injecting 110 kg N ha21 as urea–ammonium nitrate
(UAN) produced maximum NT cotton yields on Marietta fine sandy loam (fine-loamy, siliceous, active, thermic Fluvaquentic Eutrudepts). Hutchinson et al. (1995)
reported the need for a higher N rate for both CT and
NT cotton production on Gigger silt loam (fine-silty,
mixed, active, thermic Typic Fragiudalfs) having a winter wheat cover. Their research indicated that NT yields
were increased with injected N up to 78 kg ha21 when
native winter vegetation was the cover, while yields were
increased with N rates up to 118 kg ha21 with winter
wheat.
In Tennessee, cotton yields were maximized at lower
N rates than were reported for surrounding states. Yield
response to N fertilization by CT cotton on well-drained
loessial upland soils ranged from 34 kg N ha21 (Overton
and Long, 1969) to 67 kg N ha21 (Howard and Hoskinson, 1986). From a review of Tennessee research,
Howard and Hoskinson (1990) reported that CT cotton
yield responses to N fertilization varied with soil and
physiographic position. The current N recommendation
for Tennessee cotton production, regardless of tillage,
is to apply 34 to 67 kg N ha21 to alluvial soils and 67
to 90 kg N ha21 for upland soils (Univ. of Tennessee,
2000). These ranges allow the producer to select an
Abbreviations: AN, ammonium nitrate; UAN, urea–ammonium nitrate; DD60, degree days 60; NT, no-tillage; CT, conventional-tillage.
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AGRONOMY JOURNAL, VOL. 93, JANUARY–FEBRUARY 2001
N rate based on knowledge of cropping history and
previous fertilization.
Most of the previous research in the mid-South was
conducted using CT production with soil N incorporation immediately after application. Current information
on N fertilization rates and application methods for NT
cotton production on highly erodible loess-derived soils
is limited. Conservation tillage systems such as NT with
winter cover crop are recommended for erosion control
on a large portion of western Tennessee cotton land
area (Shelby and Bradley, 1996). When cropped, these
loess-derived soils historically have had high soil erosion
rates (Langdale et al., 1985) reducing productivity, especially if root-restrictive fragipans were present (Flowers
et al., 1964). Fertilizers are generally surface-applied
when CT systems are used. Surface broadcasting ureacontaining fertilizers may result in N losses from immobilization and volatilization (Reeves et al., 1993).
Howard and Essington (1998) reported that N immobilization by microorganisms in organic residues reduced
NT corn yields as much as 9%. They also reported that
the combination of immobilization and volatilization N
losses reduced NT corn yields as much as 36% from
surface-applied urea.
Surface-applied N losses by either immobilization or
volatilization from urea may reduce yields (Howard and
Essington, 1998). Injecting N below the soil surface restricts both N volatilization and immobilization since
these two loss mechanisms are primarily associated with
surface applications. However, N injection is a more
expensive application method (Roberts et al., 1995) than
surface broadcasting and should be used when either
volatilization or immobilization losses are sufficient to
reduce N yields.
The objective of this research was to evaluate the
effect of broadcast, injected, and split-applied N rates
on yields and earliness of NT cotton produced on loessderived soils.
MATERIALS AND METHODS
A 4-yr study was conducted from 1994 through 1997 on a
Loring silt loam at the Milan Experiment Station, Milan, TN.
Two-year studies were conducted from 1996 through 1997 on
a Memphis silt loam at Ames Plantation, Grand Junction,
TN, and on a Lexington silt loam at the West Tennessee
Experiment Station, Jackson, TN. A composite soil sample
was collected to a 15-cm depth from each of the replicated
blocks in 1997 to evaluate Mehlich-I extractable P and K and
organic C. For the Loring, Memphis, and Lexington silt loams,
Mehlich-I extractable P and K levels were 69 and 227 kg ha21,
75 and 138 kg ha21, and 222 and 356 kg ha21, respectively.
Total C determined with a CR-12 C Analyzer (Leco Corp.,
St. Joseph, MO) for the three soils was 11.2, 11.2, and 11.6 g
kg21, respectively.
Surface residues on the three soils were derived from volunteer native winter annuals on the Loring soil, winter wheat
on the Lexington soil, and corn stover on the Memphis soil.
The previous crop on the Loring and Lexington soils was
NT cotton, while corn was the previous crop produced on
the Memphis soil. Winter wheat was fall-seeded each year
following cotton harvest on the Lexington soil. Corn stover
from the 1995 crop was used for both the 1996 and 1997 crops.
The experimental design was a randomized complete block
with five replications. Nitrogen rates of 0, 34, 67, 101, and 134
kg N ha21 were either broadcast as AN (34% N) or injected
as urea–ammonium nitrate (UAN, 32% N) immediately after
planting. These two N sources were selected because of the
ease and accuracy of injecting liquids relative to dry fertilizers
and the potential problems associated with broadcasting UAN
for NT production (Howard and Essington, 1998). The N rate
range was selected to encompass current N rates recommended for cotton production in Tennessee (Univ. of Tennessee, 2000). Treatments were applied to the same plots each
year.
Broadcast AN treatments were hand-applied, while the injected treatments were applied using a four-row applicator.
Urea–ammonium nitrate was injected 5 cm deep and 10 cm
to the side of the row and metered through a straight stream
metering orifice attached to a knife configured behind a rolling
coulter. The N rates were applied using a CO2 pressurized
system. Injected N rates were established by varying application speed and/or orifice size. Additional treatments included
broadcasting AN at 67 kg N ha21 at planting followed by sidedressing either 34 or 67 kg N ha21 6 wk after planting (split
application). Before planting, P was broadcast at 15 kg ha21
using triple superphosphate while K was broadcast at 56 kg
ha21 using potassium chloride.
The cultivar D&PL 50 was planted from 1994 through 1996,
and D&PL 5409 was used in 1997. Experiments were planted
between early- and mid-May at all locations at approximately
190 000 seed ha21. Individual plots were four rows wide with
a 0.97-m row spacing on Lexington soil and a 1.02-m row
spacing on Loring and Memphis soils. Plot lengths were 9.1 m
at each location. Before planting, winter vegetation (wheat or
native) was killed with paraquat (1,19-dimethyl-4.49-bipyridinium ion) applied at 712 g a.i. ha21 containing 0.5% (v/v) nonionic surfactant. Residual weed control included broadcasting
pendi methalin {N-(1-ethylpropyl)-3,4-d imethyl-2,6-dinitrobenzenamine} at 930 g a.i. ha21 plus fluometuron {N,Ndimethyl-N9-[trigluoromethyl-phenyl]urea} at 1121 g a.i. ha21.
Additional recommended production practices (insecticides,
defoliants, etc.) were used at each location (Shelby, 1996).
A recommended defoliant was applied when 60% of the
bolls were open. Lint yields were determined by mechanically
picking the two center rows of each plot twice. Cotton was
picked approximately 2 wk after leaf drop with a second picking approximately 3 wk later. This interval varied due to
weather and scheduling at each location. Percent lint was
determined by combining seed cotton subsamples of individual treatments across replications and ginning on a 20-saw
gin with dual lint cleaners. Lint yields were calculated by
multiplying the lint fraction by seed cotton weights. Total lint
yields were calculated by adding the first- and second-harvest
lint yields for each treatment. The treatment effect on earliness
of maturity was evaluated as the percentage of total yield
picked at first harvest (Richmond and Ray, 1966).
Statistical analyses of lint yields and maturity (earliness)
were performed utilizing mixed model SAS procedures (SAS
Inst., 1997). The mixed model procedure provides Type III F
statistical values but does not provide mean square values for
each element within the analyses or the error terms for mean
separation. Therefore, mean separation was evaluated through
a series of protected pair-wise contrasts among all treatments
(Saxton, 1998). A probability level of 0.05 was used for mean
separation of planned comparisons. These analyses include
treatment effects on both N rates and application methods on
yields. Because separation of placement effects on yields was
difficult for certain years, broadcast and injected yield response functions were developed through regression analyses
159
HOWARD ET AL.: N FERTILIZATION OF NO-TILL COTTON
Table 1. ANOVA using mixed model F statistical values for evaluating N treatments (rates and application methods) on lint
yields, and maturity of no-till cotton produced on three soils.†
for each location and were tested for significant differences
using F-test (Chow tests) (Kennedy, 1992, p. 108–109). The
Chow Test is an F-test with T1 1 T2 2 2K degrees of freedom
and it takes the form:
Lint yields†
F 5 {[SSE (constrained) 2 SSE (unconstrained)]/K}
df
F
Year
Error a
Nitrogen (N)
Year 3 N
Error b
3
12
10
30
160
94.3
Year
Error a
Nitrogen (N)
Year 3 N
Error b
1
4
10
10
79
Year
Error a
Nitrogen (N)
Year 3 N
Error b
1
4
10
10
76
Source
[SSE(unconstrained)/(T1 1 T2 2 2K)]
where T1 and T2 are the number of observations in each of
the regressions we are comparing and K is the number of
variables in each regression including the intercept; SSE (unconstrained) is the sum of the SSEs when the two regressions
are performed separately; and SSE (constrained) is the SSE
from performing one regression using all the data from both
regressions. The latter regression using all the data essentially
constrains the parameters for both situations to be equal.
RESULTS
Experiment duration for the three locations varied
between 2 and 4 yr with each location having different
winter cover crops. The yield data as affected by N
treatment will be presented by location and winter
cover. Reference to N treatment is inclusive of the 11
treatments (N rates and application methods); otherwise, specific treatment effects will be identified and presented.
F
Loring silt loam
0.0001
23.1
44.7
3.7
0.0001
0.0001
6.5
1.6
Memphis silt loam
0.0172
3.3
15.4
17.3
0.8
78.6
Maturity‡
P.F
0.0001
0.623
P.F
0.0001
0.0001
0.0411
0.143
2.4
1.3
0.009
0.225
Lexington silt loam
0.0009
46.0
0.002
20.2
6.6
0.0001
0.0001
2.5
1.5
0.0105
0.057
† Four years of research conducted on Loring silt loam, 2 yr conducted
on both Lexington and Memphis silt loams.
‡ Maturity 5 percent of total yield picked at first harvest.
AN application resulted in similar yields as injected
UAN and broadcasted AN.
Broadcasting AN up to 67 kg N ha21 increased the
1996 yields. Except for injecting UAN at 67 kg N ha21,
the 1996 yield responses mirrored the 1994 response. A
higher N rate was required to maximize the 1997 yields,
which were increased with broadcast AN rates up to
101 kg N ha21. Injecting 67 kg N ha21 as UAN resulted
in higher yields than with broadcasting AN at 67 kg
N ha21.
Cotton yield response functions estimated for broadcasting and injecting the two N sources are presented
in Table 3. The F-tests (Chow test) indicate that the
yield response coefficients for the broadcasting AN and
injecting UAN functions were similar in 1994, 1996, and
1997. In 1995, broadcasting AN resulted in higher yields
than injecting UAN. For the annual response functions,
the yield increase with increased N rate (slope) was
higher for broadcasting AN in 1995 relative to injecting
UAN, but these differences were not significant in
other years.
Loring Silt Loam (Winter Annuals)
The N treatment (rate-placement) effects on lint
yields of cotton produced on Loring silt loam were
highly significant (P , 0.0001) but inconsistent across
the 4 yr, as indicated by a year 3 N treatment interaction
(Table 1).
Pair-wise contrasted comparisons show that the 1994
yields were increased from 962 kg ha21 for no N to 1630
kg ha21 by broadcasting 67 kg N ha21 as AN (Table
2). Yields were not increased by applying higher rates
regardless of application method. The pair-wise comparisons show that broadcasting AN or injecting UAN resulted in comparable yields for each applied N rate. The
1995 lint yields were also increased by broadcasting 67
kg N ha21 as AN but yields decreased with increased
N rates of 101 and 134 kg N ha21. Injecting either 34
or 67 kg N ha21 as UAN lowered yields compared with
broadcasting equivalent amounts of AN. Splitting the
Table 2. Effect of N rate and application method on NT cotton yields on three loess-derived soils.
N rate
Application
method†
Loring silt loam
1994
1995
1996
ha21
kg
0
34
67
101
134
34
67
101
134
101
134
1997
Lexington silt loam
Memphis
silt loam
1996
1997
821d
970c
1060b
1169a
1146a
1012bc
1046b
1044b
1069b
1149a
1167a
1396d
1637ab
1670a
1630ab
1642ab
1630ab
1542bc
1633ab
1489cd
1709a
1622ab
775e
1117d
1399b
1409b
1416b
1073d
1254c
1372bc
1290bc
1560a
1417b
ha21
B
B
B
B
I
I
I
I
SA
SA
962c*
1219b
1630a
1445a
1579a
1161bc
1432a
1501a
1581a
1508a
1600a
944de
1065bcd
1250a
1076bcd
1020cde
901e
1100bc
1193ab
1148abc
1082bcd
1165ab
514c
857b
1160a
1127a
1203a
911b
896b
1132a
1144a
1214a
1221a
kg
537e
889d
1082c
1328ab
1325ab
954cd
1225b
1299ab
1332ab
1294ab
1362a
* Within a yield column, means followed by the same letter are not significantly different at a 5 0.05.
† Application methods: B, broadcast AN; I, injected UAN; SA, split application AN.
160
AGRONOMY JOURNAL, VOL. 93, JANUARY–FEBRUARY 2001
Table 3. Regressed yield functions for broadcasting AN and injecting UAN for NT cotton produced on three loess-derived soils and
F-tests to detect differences between the application methods.
Chow test
Year
R
AM
Regressed equation
Broadcast
Loring silt loam
Y 5 954.16 1 11.53 N 2 0.054 N2
2
Injection
Broadcast
Y 5 948.56 1 8.42 N 2 0.028 N
Y 5 936.26 1 6.58 N 2 0.045 N2
0.77
0.34
Injection
Broadcast
Y 5 894.77 1 3.20 N 2 0.008 N2
Y 5 517.81 1 12.31 N 2 0.055 N2
0.45
0.82
Injection
Broadcast
Y 5 548.12 1 8.84 N 2 0.033 N2
Y 5 534.05 1 11.58 N 2 0.041 N2
0.83
0.89
Injection
Y 5 543.04 1 13.99 N 2 0.061 N2
Memphis silt loam
Y 5 817.04 1 5.25 N 2 0.02 N2
0.92
Y 5 839.16 1 4.76 N 2 0.024 N2
Lexington silt loam
Y 5 1421.34 1 6.00 N 2 0.034 N2
0.33
2
1995
1996
1997
Broadcast
Broadcast
Injection
Broadcast
Y 5 1417.01 1 5.50 N 2 0.037 N
Y 5 787.59 1 12.272 N 2 0.057 N2
0.32
0.85
Injection
Y 5 781.12 1 10.7 N 2 0.051 N2
0.75
1997
Fertilizer N treatment effects on cotton yields were
consistent across the 2 yr since the year 3 N interaction
was not significant (Table 1). Thus, the lint yield data
will be presented as 2-yr means.
Pair-wise contrasts show that 2-yr average lint yields
were increased by broadcasting AN up to 101 kg N ha21
(Table 2). However, yields were reduced by injecting
UAN at either 67 or 134 kg N ha21 compared with
broadcasting AN. Splitting the AN application resulted
in yields similar to broadcasting 101 kg N ha21 as AN.
The coefficients of yield response functions for broadcasting AN and injecting UAN were not different (Table
3). Again, the regressed equation slopes show that the
yield increase with increased N rate was similar for
broadcasting AN as for injecting UAN.
Lexington Silt Loam (Small Grain Cover)
The N treatments had a significant effect (P , 0.0001)
on lint yields of NT cotton produced on the Lexington
silt loam (Table 1). As was observed for cotton produced
on the Loring silt loam, treatment effects were inconsistent over the 2 site-years as showed by the year 3 N
treatment interaction.
The 1996 pair-wise contrasts show yields produced
on this soil were increased by either broadcasting AN
or injecting UAN at 34 kg N ha21, but higher rates did
not significantly increase yields. Injecting 134 kg N ha21
as UAN reduced yields relative to broadcasting or split
applying AN at 134 kg N ha21. In 1997, split applying
101 kg N ha21 as AN resulted in higher lint yields compared with broadcasting AN or injecting UAN at planting. Broadcasting AN at 67 kg N ha21 resulted in higher
yields relative to injecting UAN.
0.563
2.98
0.041
1.55
0.215
1.17
0.331
2.37
0.075
1.62
0.199
1.98
0.133
0.45
1996
Memphis Silt Loam (Corn Stover Cover)
0.69
0.54
1996–1997
Injection
P.F
0.64
1994
2
F
Coefficients of the two yield response functions for
either broadcasting AN or injecting UAN were not different for either 1996 and 1997 (Table 3). Once again,
yield increases with increased N rate for these two yield
functions (slope) were similar for broadcasting AN compared with injecting UAN.
Effect of Application Methods on Earliness
of Maturity
The N treatments had a highly significant effect on
earliness of cotton produced on the three soils (Table
1). The effect of these treatments on earliness was consistent across years for the Memphis and Lexington soils
but not the Loring soil as indicated by the year 3 N
treatment interaction.
In 1994, earliness of cotton produced on the Loring
silt loam was reduced by injecting UAN at 101 kg N
ha21 compared with broadcasting AN but was similar
at other rates (Table 4). Earliness was not affected by
increased N rate. In 1995, injecting UAN at 67 kg N
ha21 reduced earliness compared with broadcasting AN,
while the reverse was observed when AN was broadcast
at 134 kg N ha21. Earliness was reduced by applying
the higher N rates regardless of application method.
Injecting UAN reduced earliness in 1996 at all application rates compared with broadcasting AN. Again, earliness was reduced by applying the higher N rates regardless of application method. Differences in earliness due
to N application method were not observed in 1997.
Earliness of cotton produced on the Memphis silt
loam was reduced from injecting UAN at either 34 or
101 kg N ha21 compared with broadcasting AN. Increasing the N rate did not reduce first-harvest yields or
earliness. For the Lexington silt loam, injecting UAN
161
HOWARD ET AL.: N FERTILIZATION OF NO-TILL COTTON
Table 4. Effect of N treatments on NT cotton earliness for three loess-derived soils, expressed as the percent of total yield picked at
first harvest.
N rate
kg ha21
0
34
67
101
134
34
67
101
134
101
134
Loring silt loam
Application
method
1994
1995
1996
Broadcast
Broadcast
Broadcast
Broadcast
Inject
Inject
Inject
Inject
Split
Split
81.2a*
84.7a
85.8a
85.8a
83.9a
78.2ab
82.4a
74.4b
82.9a
82.8a
80.3ab
86.1a
85.5a
85.8a
80.2bcd
79.7cd
85.7a
81.6bcd
81.3bcd
83.2abc
83.5ab
78.6d
81.8c
88.3a
87.8ab
85.1abc
82.4c
84.1bc
83.6c
73.0e
77.2d
85.2ab
82.6c
1997
Memphis
silt loam
Lexington
silt loam
87.8ab
91.1a
88.6ab
89.1ab
87.6ab
89.3ab
88.1ab
85.5ab
84.1b
90.1a
87.7ab
79.3bcd
82.8a
79.2bcd
81.2ab
80.5abc
78.1bcd
78.6bcd
77.4cd
76.6cd
80.6abc
80.3abc
69.4d
77.8a
75.2a-d
78.9a
81.4a
77.5abc
71.1bcd
77.4abc
70.7cd
79.5a
77.6ab
%
* Within a yield column, means followed by the same letter are not significantly different at a 5 0.05.
at 134 kg N ha21 reduced earliness compared with broadcasting AN but was similar at other N rates. Averaged
across the 8 site-years of this study, injecting UAN reduced cotton earliness from 82.7 to 79.0% first-harvest
relative to broadcasting.
The pair-wise contrasts indicate earliness differences
due to the two application methods (broadcasting AN
and injecting UAN). Regressed yield equations were
developed and compared to evaluate first-harvest differences between broadcasting AN and injecting UAN
(Table 5). Evaluation of the two yield response functions for cotton produced on the Loring silt loam indicates coefficient differences in 1995 and 1996 with no
differences in 1994 and 1997. These differences were
not observed for total yields, except for 1995 (Table 3).
Response coefficient differences between broadcasting
AN and injecting UAN were also observed for cotton
produced on the Memphis silt loam and the 1996 yields
produced on the Lexington silt loam (Table 5). For the
three locations, the regressed coefficients for broadcast-
ing AN were greater than for injecting UAN in 5 of the
8 site-years.
DISCUSSION
Broadcasting N was a satisfactory application method
for NT cotton production in this study. Surface residues,
normally associated with NT production, did not reduce
yields as observed in other cotton research (Hutchinson
et al., 1995; Thompson and Varco, 1996) or as observed
with NT corn (Howard and Essington, 1998). Yields on
the Loring soil having the native winter weed vegetation
were maximized by broadcasting 67 kg N ha21. Injecting
N as UAN did not increase yields, suggesting that possible N immobilization by surface residue was insufficient
to reduce yields. This observation differs with the findings of Thompson and Varco (1996). They reported the
need to broadcast a higher N rate compared with the
injected N rate for NT cotton production in Mississippi.
In this study, a higher N rate (101 kg N ha21) was needed
Table 5. Regressed functions for broadcasting AN and injecting UAN on first harvest yields of NT cotton produced on three loessderived soils and F-tests to detect differences between application methods.
Year
Chow test
Application
method
Regressed equation
Broadcast
Loring silt loam
Y 5 774.35 1 11.08 N 2 0.054 N2
2
R
Injection
Broadcast
2
Y 5 775.17 1 5.51 N 2 0.013 N
Y 5 808.37 1 5.54 N 2 0.042 N2
0.60
0.39
Injection
Broadcast
Y 5 778.68 1 1.61 N 2 0.001 N2
Y 5 426.36 1 11.97 N 2 0.06 N2
0.36
0.83
Injection
Broadcast
Y 5 461.45 1 7.13 N 2 0.031 N2
Y 5 472.73 1 10.70 N 2 0.041 N2
0.69
0.89
Injection
Y 5 480.58 1 12.62 N 2 0.059 N2
Memphis silt loam
Y 5 655.54 1 4.36 N 2 0.017 N2
0.83
0.28
Broadcast
Y 5 662.73 1 3.61 N 2 0.019 N2
Lexington silt loam
Y 5 1057.16 1 2.11 N 2 0.006 N2
Injection
Broadcast
NS
Y 5 528.37 1 13.49 N 2 0.063 N2
1995
1996
1997
Y 5 522.81 1 11.41 N 2 0.057 N
4.76
0.006
5.42
0.003
0.720
0.545
4.53
0.005
3.39
0.026
1.91
0.144
0.74
1997
Injection
0.054
0.34
1996
2
2.74
0.53
1996–1997
Injection
P.F
0.71
1994
Broadcast
F
0.59
162
AGRONOMY JOURNAL, VOL. 93, JANUARY–FEBRUARY 2001
for NT cotton produced on the Memphis silt loam having the corn stover cover, but yields were not improved
by injecting N. Yields produced on the Lexington silt
loam having a winter wheat cover were reduced by
injecting UAN 67 kg N ha21 compared with broadcasting AN at 67 kg N ha21. This observation differs with
the findings of Hutchinson et al. (1995). They reported
the need for an extra 37 kg N ha21 to cotton produced
on soils having a wheat winter cover. Previous research
showed reduced NT corn yields from broadcasting AN
compared with injecting UAN on a soil that had been
in NT production 12 to 15 yr (Howard and Essington,
1998). However, they reported no yield reduction from
broadcasting AN on a soil that had been in NT for 2
to 5 yr. Several factors were speculated to explain the
difference. One speculation was that the higher organic
matter (resulting from long-term NT production using
winter wheat as cover) was immobilizing sufficient N
to reduce yields. These data indicate that injecting UAN
for NT cotton production on these soils is questionable
based on the expenses of the application method (Roberts et al., 1995).
Split N applications increased yields only 1 of the 8
site-years. Unfortunately, the split N rates (101 and 134
kg N ha21) may have been too high for this research.
Because of the limited frequency of yield response (1 yr
in 8) in this research, split N application for cotton
production is questionable due to the expense involved
with the extra trip over the field and equipment costs.
Injecting N delayed crop maturity in some site-years
compared with broadcasting AN. Several factors can be
speculated for this delayed crop maturity. One factor
may be the difference in N sources (UAN and AN)
and application method (injected vs. broadcast). The
injected UAN source contains 25% NH4–N and 50%
NH2–N, whereas AN contains 50% NH4–N. The conversion of urea-N to NO3–N may require more time than
the conversion of AN–N to NO3–N. An additional factor
that may affect earliness is possibly greater N concentration resulting from the injection application method
(Howard and Essington, 1998). Surface broadcasting N
over the soil increases the probability of N immobilization by microbial activity reducing N concentration, at
least temporarily. Injecting UAN reduces N immobilization and should provide a higher N concentration within
the restricted application zone. Increased N concentration from broadcasting higher N rates has been reported
to delay cotton maturity and reduce yields (Boquet et
al., 1994; Hutchinson et al., 1995; Maples and Keogh,
1971; McConnell et al., 1993; McConnell et al., 1995).
Crop maturity is a critical production consideration
for cotton producers along the northern edge of the
U.S. Cotton Belt (Gwathmey and Howard, 1998). Practices that delay maturity often reduce yields because
of reduced heat-unit (DD60) accumulation during the
latter part of the growing season. For instance, crop
maturity of cotton produced on the Lexington silt loam
was reduced both years by injecting the N. The accumulated DD60s between planting and first harvest were
2195 and 2190 for 1996 and 1997, respectively. In 1996,
a total of 27 DD60s were accumulated between first
and second harvest periods. In 1997, only one DD60 was
accumulated between first and second harvest periods.
Heat-unit accumulation for the three soils was similar,
and data for the remaining two are not reported. Limited heat-unit accumulation in this region indicates the
need to identify treatments that are conducive to earliness. However, treatments that delay cotton maturity
and promote higher second-harvest yields may be desirable for producers in areas having a greater heat-unit
accumulation potential after first harvest.
CONCLUSIONS
Broadcasting N as AN was a satisfactory application
method for NT cotton production on three loess-derived
soils having different winter covers. Lint yields were
maximized by applying 67 kg N ha21 on the Loring and
Lexington silt loams but 101 kg N ha21 was required to
maximize yields on the Memphis silt loam. Lint yields
were greater in 1 of 8 site-years from broadcasting AN
compared with injecting UAN. Split N applications of
AN resulted in higher yields in only 1 of 8 site-years
relative to broadcasting AN at planting. The extra time
and expense of the split N applications or injecting N
do not justify the added time and expense for cotton
production on these soils. Crop earliness (maturity) was
improved from 79.0 to 82.7% first-harvest on average,
across the 8 site-years by broadcasting N compared with
injection. This may improve the likelihood that cotton
can be harvested before a killing frost along the northern
edge of the U.S. Cotton Belt.
ACKNOWLEDGMENTS
The authors acknowledge the cooperation of the Ames
Plantation staff under terms of a perpetual trust to the University of Tennessee by Julia C. Ames. We also acknowledge the
staff members located at the Milan Experiment Station, Milan,
TN, and the West Tennessee Experiment Station, Jackson,
TN, for their cooperation and efforts in this research.
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Statement of Ethics
American Society of Agronomy
Members of the American Society of Agronomy acknowledge that they are scientifically and
professionally involved with the interdependence of natural, social, and technological systems.
They are dedicated to the acquisition and dissemination of knowledge that advances the sciences
and professions involving plants, soils, and their environment.
In an effort to promote the highest quality of scientific and professional conduct among its
members, the American Society of Agronomy endorses the following guiding principles, which
represent basic scientific and professional values of our profession.
Members shall:
1. Uphold the highest standards of scientific investigation and professional comportment, and
an uncompromising commitment to the advancement of knowledge.
2. Honor the rights and accomplishments of others and properly credit the work and ideas
of others.
3. Strive to avoid conflicts of interest.
4. Demonstrate social responsibility in scientific and professional practice, by considering
whom their scientific and professional activities benefit, and whom they neglect.
5. Provide honest and impartial advice on subjects about which they are informed and
qualified.
6. As mentors of the next generation of scientific and professional leaders, strive to instill
these ethical standards in students at all educational levels.
Approved by the ASA Board of Directors, 1 Nov. 1992
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Nitrogen Fertilization of No-Till Cotton on Loess-Derived Soils
Donald D. Howard,* C. Owen Gwathmey, Michael E. Essington, Roland K. Roberts, and Mike D. Mullen
ABSTRACT
Information on nitrogen (N) fertilization of no-till (NT) cotton
(Gossypium hirsutum L.) is needed to optimize lint yields and earliness. We evaluated five N rates and three application methods for
NT cotton production on Loring silt loam (fine-silty, mixed, active,
thermic Oxyaquic Fragiudalfs) with natural winter annuals as a cover;
and on Memphis silt loam (fine-silty, mixed, active, thermic Typic
Hapludalfs) having corn (Zea mays L.) stover as a cover and on
Lexington silt loam (fine-silty, mixed, active, thermic Utlic Hapludalfs)
having winter wheat (Triticum aestivum L.) as a cover. Nitrogen rates
of 0, 34, 67, 101, and 134 kg ha21 were either broadcasted as ammonium nitrate (AN) or injected as urea–ammonium nitrate (UAN) at
planting. Additional treatments included broadcasting 67 kg N ha21
as AN at planting with either 34 or 67 kg N ha21 banded 6 wk later.
Relative to no N, broadcasting 67 kg N ha21 as AN increased 4-yr
average NT lint yields on Loring silt loam from 739 to 1281 kg lint
ha21 and 2-yr average yields on Lexington silt loam from 1086 to 1535
kg ha21. A higher N rate (101 kg N ha21) was needed to increase 2yr average yields on Memphis silt loam from 821 to 1169 kg ha21.
Broadcasting AN was a satisfactory placement method producing
yields equal to or higher than injecting UAN or splitting AN for
NT cotton produced on these loessial soils despite different covers
and residues.
N
itrogen (N) fertilization affects yield, maturity, and
lint quality of cotton. Evaluating N rates, sources,
and application timing for optimum lint production has
been a major research emphasis within the cotton producing states. For cotton, applying an optimum N rate
is essential and may differ within the production areas
due to climatic or soil differences. An optimum N rate
should maximize yields, while excessive or inadequate
N applications may reduce cotton yields (Maples and
Keogh, 1971). High N fertilization may produce excessive vegetation that delays maturity and harvest, and
these conditions may reduce yields and lint quality during years of early frost or prolonged fall rain (Hutchinson et al., 1995; McConnell et al., 1995). Crop maturity is
a critical production consideration for cotton producers
along the northern edge of the U.S. Cotton Belt (Gwathmey and Howard, 1998). Nitrogen deficiency causes preD.D. Howard and C.O. Gwathmey, Plant and Soil Sciences Dep.,
Univ. of Tennessee, West Tennessee Exp. Stn., Jackson, TN 38301;
M.E. Essington and M.D. Mullen, Plant and Soil Sciences Dep., Univ.
of Tennessee, P.O. Box 1071, Knoxville, TN 37901-1071; and R.K.
Roberts, Agric. Economics and Rural Sociology Dep., Univ. of Tennessee, P.O. Box 1071, Knoxville, TN 37901-1071. Received 26 Jan.
2000. *Corresponding author (dhoward2@utk.edu).
Published in Agron. J. 93:157–163 (2001).
mature senescence and reduced yields (McConnell et
al., 1995).
Research conducted within the mid-South shows that
the optimum N rate for cotton production varies with
location, soil type, tillage system, winter cover, and application method. On conventionally tilled (CT) Dundee very fine sandy loam (fine-silty, mixed, active, thermic Typic Endoaqualfs), Ebelhar and Welch (1996)
reported optimum yields from banding 50% of the N
at planting followed by banding 50% at pinhead square.
Their evaluation included N rates (67–168 kg ha21) and
application timing (at planting and three splits) from
which they concluded that the 50–50 split application
of 101 kg N ha21 resulted in the highest yields. In an
additional study, Ebelhar et al. (1996) showed that injecting a 50–50 split (at planting and pinhead) at a higher
rate (134 kg N ha21) resulted in maximum cotton yields
on CT Bosket very fine sandy loam (fine-silty, mixed,
active, thermic Typic Hapludalfs) and Dubbs silt loam
(fine-silty, mixed, active, thermic Typic Hapludalfs). In
Mississippi, Thompson and Varco (1996) reported that
broadcasting 121 kg N ha21 as ammonium nitrate (AN)
and injecting 110 kg N ha21 as urea–ammonium nitrate
(UAN) produced maximum NT cotton yields on Marietta fine sandy loam (fine-loamy, siliceous, active, thermic Fluvaquentic Eutrudepts). Hutchinson et al. (1995)
reported the need for a higher N rate for both CT and
NT cotton production on Gigger silt loam (fine-silty,
mixed, active, thermic Typic Fragiudalfs) having a winter wheat cover. Their research indicated that NT yields
were increased with injected N up to 78 kg ha21 when
native winter vegetation was the cover, while yields were
increased with N rates up to 118 kg ha21 with winter
wheat.
In Tennessee, cotton yields were maximized at lower
N rates than were reported for surrounding states. Yield
response to N fertilization by CT cotton on well-drained
loessial upland soils ranged from 34 kg N ha21 (Overton
and Long, 1969) to 67 kg N ha21 (Howard and Hoskinson, 1986). From a review of Tennessee research,
Howard and Hoskinson (1990) reported that CT cotton
yield responses to N fertilization varied with soil and
physiographic position. The current N recommendation
for Tennessee cotton production, regardless of tillage,
is to apply 34 to 67 kg N ha21 to alluvial soils and 67
to 90 kg N ha21 for upland soils (Univ. of Tennessee,
2000). These ranges allow the producer to select an
Abbreviations: AN, ammonium nitrate; UAN, urea–ammonium nitrate; DD60, degree days 60; NT, no-tillage; CT, conventional-tillage.
158
AGRONOMY JOURNAL, VOL. 93, JANUARY–FEBRUARY 2001
N rate based on knowledge of cropping history and
previous fertilization.
Most of the previous research in the mid-South was
conducted using CT production with soil N incorporation immediately after application. Current information
on N fertilization rates and application methods for NT
cotton production on highly erodible loess-derived soils
is limited. Conservation tillage systems such as NT with
winter cover crop are recommended for erosion control
on a large portion of western Tennessee cotton land
area (Shelby and Bradley, 1996). When cropped, these
loess-derived soils historically have had high soil erosion
rates (Langdale et al., 1985) reducing productivity, especially if root-restrictive fragipans were present (Flowers
et al., 1964). Fertilizers are generally surface-applied
when CT systems are used. Surface broadcasting ureacontaining fertilizers may result in N losses from immobilization and volatilization (Reeves et al., 1993).
Howard and Essington (1998) reported that N immobilization by microorganisms in organic residues reduced
NT corn yields as much as 9%. They also reported that
the combination of immobilization and volatilization N
losses reduced NT corn yields as much as 36% from
surface-applied urea.
Surface-applied N losses by either immobilization or
volatilization from urea may reduce yields (Howard and
Essington, 1998). Injecting N below the soil surface restricts both N volatilization and immobilization since
these two loss mechanisms are primarily associated with
surface applications. However, N injection is a more
expensive application method (Roberts et al., 1995) than
surface broadcasting and should be used when either
volatilization or immobilization losses are sufficient to
reduce N yields.
The objective of this research was to evaluate the
effect of broadcast, injected, and split-applied N rates
on yields and earliness of NT cotton produced on loessderived soils.
MATERIALS AND METHODS
A 4-yr study was conducted from 1994 through 1997 on a
Loring silt loam at the Milan Experiment Station, Milan, TN.
Two-year studies were conducted from 1996 through 1997 on
a Memphis silt loam at Ames Plantation, Grand Junction,
TN, and on a Lexington silt loam at the West Tennessee
Experiment Station, Jackson, TN. A composite soil sample
was collected to a 15-cm depth from each of the replicated
blocks in 1997 to evaluate Mehlich-I extractable P and K and
organic C. For the Loring, Memphis, and Lexington silt loams,
Mehlich-I extractable P and K levels were 69 and 227 kg ha21,
75 and 138 kg ha21, and 222 and 356 kg ha21, respectively.
Total C determined with a CR-12 C Analyzer (Leco Corp.,
St. Joseph, MO) for the three soils was 11.2, 11.2, and 11.6 g
kg21, respectively.
Surface residues on the three soils were derived from volunteer native winter annuals on the Loring soil, winter wheat
on the Lexington soil, and corn stover on the Memphis soil.
The previous crop on the Loring and Lexington soils was
NT cotton, while corn was the previous crop produced on
the Memphis soil. Winter wheat was fall-seeded each year
following cotton harvest on the Lexington soil. Corn stover
from the 1995 crop was used for both the 1996 and 1997 crops.
The experimental design was a randomized complete block
with five replications. Nitrogen rates of 0, 34, 67, 101, and 134
kg N ha21 were either broadcast as AN (34% N) or injected
as urea–ammonium nitrate (UAN, 32% N) immediately after
planting. These two N sources were selected because of the
ease and accuracy of injecting liquids relative to dry fertilizers
and the potential problems associated with broadcasting UAN
for NT production (Howard and Essington, 1998). The N rate
range was selected to encompass current N rates recommended for cotton production in Tennessee (Univ. of Tennessee, 2000). Treatments were applied to the same plots each
year.
Broadcast AN treatments were hand-applied, while the injected treatments were applied using a four-row applicator.
Urea–ammonium nitrate was injected 5 cm deep and 10 cm
to the side of the row and metered through a straight stream
metering orifice attached to a knife configured behind a rolling
coulter. The N rates were applied using a CO2 pressurized
system. Injected N rates were established by varying application speed and/or orifice size. Additional treatments included
broadcasting AN at 67 kg N ha21 at planting followed by sidedressing either 34 or 67 kg N ha21 6 wk after planting (split
application). Before planting, P was broadcast at 15 kg ha21
using triple superphosphate while K was broadcast at 56 kg
ha21 using potassium chloride.
The cultivar D&PL 50 was planted from 1994 through 1996,
and D&PL 5409 was used in 1997. Experiments were planted
between early- and mid-May at all locations at approximately
190 000 seed ha21. Individual plots were four rows wide with
a 0.97-m row spacing on Lexington soil and a 1.02-m row
spacing on Loring and Memphis soils. Plot lengths were 9.1 m
at each location. Before planting, winter vegetation (wheat or
native) was killed with paraquat (1,19-dimethyl-4.49-bipyridinium ion) applied at 712 g a.i. ha21 containing 0.5% (v/v) nonionic surfactant. Residual weed control included broadcasting
pendi methalin {N-(1-ethylpropyl)-3,4-d imethyl-2,6-dinitrobenzenamine} at 930 g a.i. ha21 plus fluometuron {N,Ndimethyl-N9-[trigluoromethyl-phenyl]urea} at 1121 g a.i. ha21.
Additional recommended production practices (insecticides,
defoliants, etc.) were used at each location (Shelby, 1996).
A recommended defoliant was applied when 60% of the
bolls were open. Lint yields were determined by mechanically
picking the two center rows of each plot twice. Cotton was
picked approximately 2 wk after leaf drop with a second picking approximately 3 wk later. This interval varied due to
weather and scheduling at each location. Percent lint was
determined by combining seed cotton subsamples of individual treatments across replications and ginning on a 20-saw
gin with dual lint cleaners. Lint yields were calculated by
multiplying the lint fraction by seed cotton weights. Total lint
yields were calculated by adding the first- and second-harvest
lint yields for each treatment. The treatment effect on earliness
of maturity was evaluated as the percentage of total yield
picked at first harvest (Richmond and Ray, 1966).
Statistical analyses of lint yields and maturity (earliness)
were performed utilizing mixed model SAS procedures (SAS
Inst., 1997). The mixed model procedure provides Type III F
statistical values but does not provide mean square values for
each element within the analyses or the error terms for mean
separation. Therefore, mean separation was evaluated through
a series of protected pair-wise contrasts among all treatments
(Saxton, 1998). A probability level of 0.05 was used for mean
separation of planned comparisons. These analyses include
treatment effects on both N rates and application methods on
yields. Because separation of placement effects on yields was
difficult for certain years, broadcast and injected yield response functions were developed through regression analyses
159
HOWARD ET AL.: N FERTILIZATION OF NO-TILL COTTON
Table 1. ANOVA using mixed model F statistical values for evaluating N treatments (rates and application methods) on lint
yields, and maturity of no-till cotton produced on three soils.†
for each location and were tested for significant differences
using F-test (Chow tests) (Kennedy, 1992, p. 108–109). The
Chow Test is an F-test with T1 1 T2 2 2K degrees of freedom
and it takes the form:
Lint yields†
F 5 {[SSE (constrained) 2 SSE (unconstrained)]/K}
df
F
Year
Error a
Nitrogen (N)
Year 3 N
Error b
3
12
10
30
160
94.3
Year
Error a
Nitrogen (N)
Year 3 N
Error b
1
4
10
10
79
Year
Error a
Nitrogen (N)
Year 3 N
Error b
1
4
10
10
76
Source
[SSE(unconstrained)/(T1 1 T2 2 2K)]
where T1 and T2 are the number of observations in each of
the regressions we are comparing and K is the number of
variables in each regression including the intercept; SSE (unconstrained) is the sum of the SSEs when the two regressions
are performed separately; and SSE (constrained) is the SSE
from performing one regression using all the data from both
regressions. The latter regression using all the data essentially
constrains the parameters for both situations to be equal.
RESULTS
Experiment duration for the three locations varied
between 2 and 4 yr with each location having different
winter cover crops. The yield data as affected by N
treatment will be presented by location and winter
cover. Reference to N treatment is inclusive of the 11
treatments (N rates and application methods); otherwise, specific treatment effects will be identified and presented.
F
Loring silt loam
0.0001
23.1
44.7
3.7
0.0001
0.0001
6.5
1.6
Memphis silt loam
0.0172
3.3
15.4
17.3
0.8
78.6
Maturity‡
P.F
0.0001
0.623
P.F
0.0001
0.0001
0.0411
0.143
2.4
1.3
0.009
0.225
Lexington silt loam
0.0009
46.0
0.002
20.2
6.6
0.0001
0.0001
2.5
1.5
0.0105
0.057
† Four years of research conducted on Loring silt loam, 2 yr conducted
on both Lexington and Memphis silt loams.
‡ Maturity 5 percent of total yield picked at first harvest.
AN application resulted in similar yields as injected
UAN and broadcasted AN.
Broadcasting AN up to 67 kg N ha21 increased the
1996 yields. Except for injecting UAN at 67 kg N ha21,
the 1996 yield responses mirrored the 1994 response. A
higher N rate was required to maximize the 1997 yields,
which were increased with broadcast AN rates up to
101 kg N ha21. Injecting 67 kg N ha21 as UAN resulted
in higher yields than with broadcasting AN at 67 kg
N ha21.
Cotton yield response functions estimated for broadcasting and injecting the two N sources are presented
in Table 3. The F-tests (Chow test) indicate that the
yield response coefficients for the broadcasting AN and
injecting UAN functions were similar in 1994, 1996, and
1997. In 1995, broadcasting AN resulted in higher yields
than injecting UAN. For the annual response functions,
the yield increase with increased N rate (slope) was
higher for broadcasting AN in 1995 relative to injecting
UAN, but these differences were not significant in
other years.
Loring Silt Loam (Winter Annuals)
The N treatment (rate-placement) effects on lint
yields of cotton produced on Loring silt loam were
highly significant (P , 0.0001) but inconsistent across
the 4 yr, as indicated by a year 3 N treatment interaction
(Table 1).
Pair-wise contrasted comparisons show that the 1994
yields were increased from 962 kg ha21 for no N to 1630
kg ha21 by broadcasting 67 kg N ha21 as AN (Table
2). Yields were not increased by applying higher rates
regardless of application method. The pair-wise comparisons show that broadcasting AN or injecting UAN resulted in comparable yields for each applied N rate. The
1995 lint yields were also increased by broadcasting 67
kg N ha21 as AN but yields decreased with increased
N rates of 101 and 134 kg N ha21. Injecting either 34
or 67 kg N ha21 as UAN lowered yields compared with
broadcasting equivalent amounts of AN. Splitting the
Table 2. Effect of N rate and application method on NT cotton yields on three loess-derived soils.
N rate
Application
method†
Loring silt loam
1994
1995
1996
ha21
kg
0
34
67
101
134
34
67
101
134
101
134
1997
Lexington silt loam
Memphis
silt loam
1996
1997
821d
970c
1060b
1169a
1146a
1012bc
1046b
1044b
1069b
1149a
1167a
1396d
1637ab
1670a
1630ab
1642ab
1630ab
1542bc
1633ab
1489cd
1709a
1622ab
775e
1117d
1399b
1409b
1416b
1073d
1254c
1372bc
1290bc
1560a
1417b
ha21
B
B
B
B
I
I
I
I
SA
SA
962c*
1219b
1630a
1445a
1579a
1161bc
1432a
1501a
1581a
1508a
1600a
944de
1065bcd
1250a
1076bcd
1020cde
901e
1100bc
1193ab
1148abc
1082bcd
1165ab
514c
857b
1160a
1127a
1203a
911b
896b
1132a
1144a
1214a
1221a
kg
537e
889d
1082c
1328ab
1325ab
954cd
1225b
1299ab
1332ab
1294ab
1362a
* Within a yield column, means followed by the same letter are not significantly different at a 5 0.05.
† Application methods: B, broadcast AN; I, injected UAN; SA, split application AN.
160
AGRONOMY JOURNAL, VOL. 93, JANUARY–FEBRUARY 2001
Table 3. Regressed yield functions for broadcasting AN and injecting UAN for NT cotton produced on three loess-derived soils and
F-tests to detect differences between the application methods.
Chow test
Year
R
AM
Regressed equation
Broadcast
Loring silt loam
Y 5 954.16 1 11.53 N 2 0.054 N2
2
Injection
Broadcast
Y 5 948.56 1 8.42 N 2 0.028 N
Y 5 936.26 1 6.58 N 2 0.045 N2
0.77
0.34
Injection
Broadcast
Y 5 894.77 1 3.20 N 2 0.008 N2
Y 5 517.81 1 12.31 N 2 0.055 N2
0.45
0.82
Injection
Broadcast
Y 5 548.12 1 8.84 N 2 0.033 N2
Y 5 534.05 1 11.58 N 2 0.041 N2
0.83
0.89
Injection
Y 5 543.04 1 13.99 N 2 0.061 N2
Memphis silt loam
Y 5 817.04 1 5.25 N 2 0.02 N2
0.92
Y 5 839.16 1 4.76 N 2 0.024 N2
Lexington silt loam
Y 5 1421.34 1 6.00 N 2 0.034 N2
0.33
2
1995
1996
1997
Broadcast
Broadcast
Injection
Broadcast
Y 5 1417.01 1 5.50 N 2 0.037 N
Y 5 787.59 1 12.272 N 2 0.057 N2
0.32
0.85
Injection
Y 5 781.12 1 10.7 N 2 0.051 N2
0.75
1997
Fertilizer N treatment effects on cotton yields were
consistent across the 2 yr since the year 3 N interaction
was not significant (Table 1). Thus, the lint yield data
will be presented as 2-yr means.
Pair-wise contrasts show that 2-yr average lint yields
were increased by broadcasting AN up to 101 kg N ha21
(Table 2). However, yields were reduced by injecting
UAN at either 67 or 134 kg N ha21 compared with
broadcasting AN. Splitting the AN application resulted
in yields similar to broadcasting 101 kg N ha21 as AN.
The coefficients of yield response functions for broadcasting AN and injecting UAN were not different (Table
3). Again, the regressed equation slopes show that the
yield increase with increased N rate was similar for
broadcasting AN as for injecting UAN.
Lexington Silt Loam (Small Grain Cover)
The N treatments had a significant effect (P , 0.0001)
on lint yields of NT cotton produced on the Lexington
silt loam (Table 1). As was observed for cotton produced
on the Loring silt loam, treatment effects were inconsistent over the 2 site-years as showed by the year 3 N
treatment interaction.
The 1996 pair-wise contrasts show yields produced
on this soil were increased by either broadcasting AN
or injecting UAN at 34 kg N ha21, but higher rates did
not significantly increase yields. Injecting 134 kg N ha21
as UAN reduced yields relative to broadcasting or split
applying AN at 134 kg N ha21. In 1997, split applying
101 kg N ha21 as AN resulted in higher lint yields compared with broadcasting AN or injecting UAN at planting. Broadcasting AN at 67 kg N ha21 resulted in higher
yields relative to injecting UAN.
0.563
2.98
0.041
1.55
0.215
1.17
0.331
2.37
0.075
1.62
0.199
1.98
0.133
0.45
1996
Memphis Silt Loam (Corn Stover Cover)
0.69
0.54
1996–1997
Injection
P.F
0.64
1994
2
F
Coefficients of the two yield response functions for
either broadcasting AN or injecting UAN were not different for either 1996 and 1997 (Table 3). Once again,
yield increases with increased N rate for these two yield
functions (slope) were similar for broadcasting AN compared with injecting UAN.
Effect of Application Methods on Earliness
of Maturity
The N treatments had a highly significant effect on
earliness of cotton produced on the three soils (Table
1). The effect of these treatments on earliness was consistent across years for the Memphis and Lexington soils
but not the Loring soil as indicated by the year 3 N
treatment interaction.
In 1994, earliness of cotton produced on the Loring
silt loam was reduced by injecting UAN at 101 kg N
ha21 compared with broadcasting AN but was similar
at other rates (Table 4). Earliness was not affected by
increased N rate. In 1995, injecting UAN at 67 kg N
ha21 reduced earliness compared with broadcasting AN,
while the reverse was observed when AN was broadcast
at 134 kg N ha21. Earliness was reduced by applying
the higher N rates regardless of application method.
Injecting UAN reduced earliness in 1996 at all application rates compared with broadcasting AN. Again, earliness was reduced by applying the higher N rates regardless of application method. Differences in earliness due
to N application method were not observed in 1997.
Earliness of cotton produced on the Memphis silt
loam was reduced from injecting UAN at either 34 or
101 kg N ha21 compared with broadcasting AN. Increasing the N rate did not reduce first-harvest yields or
earliness. For the Lexington silt loam, injecting UAN
161
HOWARD ET AL.: N FERTILIZATION OF NO-TILL COTTON
Table 4. Effect of N treatments on NT cotton earliness for three loess-derived soils, expressed as the percent of total yield picked at
first harvest.
N rate
kg ha21
0
34
67
101
134
34
67
101
134
101
134
Loring silt loam
Application
method
1994
1995
1996
Broadcast
Broadcast
Broadcast
Broadcast
Inject
Inject
Inject
Inject
Split
Split
81.2a*
84.7a
85.8a
85.8a
83.9a
78.2ab
82.4a
74.4b
82.9a
82.8a
80.3ab
86.1a
85.5a
85.8a
80.2bcd
79.7cd
85.7a
81.6bcd
81.3bcd
83.2abc
83.5ab
78.6d
81.8c
88.3a
87.8ab
85.1abc
82.4c
84.1bc
83.6c
73.0e
77.2d
85.2ab
82.6c
1997
Memphis
silt loam
Lexington
silt loam
87.8ab
91.1a
88.6ab
89.1ab
87.6ab
89.3ab
88.1ab
85.5ab
84.1b
90.1a
87.7ab
79.3bcd
82.8a
79.2bcd
81.2ab
80.5abc
78.1bcd
78.6bcd
77.4cd
76.6cd
80.6abc
80.3abc
69.4d
77.8a
75.2a-d
78.9a
81.4a
77.5abc
71.1bcd
77.4abc
70.7cd
79.5a
77.6ab
%
* Within a yield column, means followed by the same letter are not significantly different at a 5 0.05.
at 134 kg N ha21 reduced earliness compared with broadcasting AN but was similar at other N rates. Averaged
across the 8 site-years of this study, injecting UAN reduced cotton earliness from 82.7 to 79.0% first-harvest
relative to broadcasting.
The pair-wise contrasts indicate earliness differences
due to the two application methods (broadcasting AN
and injecting UAN). Regressed yield equations were
developed and compared to evaluate first-harvest differences between broadcasting AN and injecting UAN
(Table 5). Evaluation of the two yield response functions for cotton produced on the Loring silt loam indicates coefficient differences in 1995 and 1996 with no
differences in 1994 and 1997. These differences were
not observed for total yields, except for 1995 (Table 3).
Response coefficient differences between broadcasting
AN and injecting UAN were also observed for cotton
produced on the Memphis silt loam and the 1996 yields
produced on the Lexington silt loam (Table 5). For the
three locations, the regressed coefficients for broadcast-
ing AN were greater than for injecting UAN in 5 of the
8 site-years.
DISCUSSION
Broadcasting N was a satisfactory application method
for NT cotton production in this study. Surface residues,
normally associated with NT production, did not reduce
yields as observed in other cotton research (Hutchinson
et al., 1995; Thompson and Varco, 1996) or as observed
with NT corn (Howard and Essington, 1998). Yields on
the Loring soil having the native winter weed vegetation
were maximized by broadcasting 67 kg N ha21. Injecting
N as UAN did not increase yields, suggesting that possible N immobilization by surface residue was insufficient
to reduce yields. This observation differs with the findings of Thompson and Varco (1996). They reported the
need to broadcast a higher N rate compared with the
injected N rate for NT cotton production in Mississippi.
In this study, a higher N rate (101 kg N ha21) was needed
Table 5. Regressed functions for broadcasting AN and injecting UAN on first harvest yields of NT cotton produced on three loessderived soils and F-tests to detect differences between application methods.
Year
Chow test
Application
method
Regressed equation
Broadcast
Loring silt loam
Y 5 774.35 1 11.08 N 2 0.054 N2
2
R
Injection
Broadcast
2
Y 5 775.17 1 5.51 N 2 0.013 N
Y 5 808.37 1 5.54 N 2 0.042 N2
0.60
0.39
Injection
Broadcast
Y 5 778.68 1 1.61 N 2 0.001 N2
Y 5 426.36 1 11.97 N 2 0.06 N2
0.36
0.83
Injection
Broadcast
Y 5 461.45 1 7.13 N 2 0.031 N2
Y 5 472.73 1 10.70 N 2 0.041 N2
0.69
0.89
Injection
Y 5 480.58 1 12.62 N 2 0.059 N2
Memphis silt loam
Y 5 655.54 1 4.36 N 2 0.017 N2
0.83
0.28
Broadcast
Y 5 662.73 1 3.61 N 2 0.019 N2
Lexington silt loam
Y 5 1057.16 1 2.11 N 2 0.006 N2
Injection
Broadcast
NS
Y 5 528.37 1 13.49 N 2 0.063 N2
1995
1996
1997
Y 5 522.81 1 11.41 N 2 0.057 N
4.76
0.006
5.42
0.003
0.720
0.545
4.53
0.005
3.39
0.026
1.91
0.144
0.74
1997
Injection
0.054
0.34
1996
2
2.74
0.53
1996–1997
Injection
P.F
0.71
1994
Broadcast
F
0.59
162
AGRONOMY JOURNAL, VOL. 93, JANUARY–FEBRUARY 2001
for NT cotton produced on the Memphis silt loam having the corn stover cover, but yields were not improved
by injecting N. Yields produced on the Lexington silt
loam having a winter wheat cover were reduced by
injecting UAN 67 kg N ha21 compared with broadcasting AN at 67 kg N ha21. This observation differs with
the findings of Hutchinson et al. (1995). They reported
the need for an extra 37 kg N ha21 to cotton produced
on soils having a wheat winter cover. Previous research
showed reduced NT corn yields from broadcasting AN
compared with injecting UAN on a soil that had been
in NT production 12 to 15 yr (Howard and Essington,
1998). However, they reported no yield reduction from
broadcasting AN on a soil that had been in NT for 2
to 5 yr. Several factors were speculated to explain the
difference. One speculation was that the higher organic
matter (resulting from long-term NT production using
winter wheat as cover) was immobilizing sufficient N
to reduce yields. These data indicate that injecting UAN
for NT cotton production on these soils is questionable
based on the expenses of the application method (Roberts et al., 1995).
Split N applications increased yields only 1 of the 8
site-years. Unfortunately, the split N rates (101 and 134
kg N ha21) may have been too high for this research.
Because of the limited frequency of yield response (1 yr
in 8) in this research, split N application for cotton
production is questionable due to the expense involved
with the extra trip over the field and equipment costs.
Injecting N delayed crop maturity in some site-years
compared with broadcasting AN. Several factors can be
speculated for this delayed crop maturity. One factor
may be the difference in N sources (UAN and AN)
and application method (injected vs. broadcast). The
injected UAN source contains 25% NH4–N and 50%
NH2–N, whereas AN contains 50% NH4–N. The conversion of urea-N to NO3–N may require more time than
the conversion of AN–N to NO3–N. An additional factor
that may affect earliness is possibly greater N concentration resulting from the injection application method
(Howard and Essington, 1998). Surface broadcasting N
over the soil increases the probability of N immobilization by microbial activity reducing N concentration, at
least temporarily. Injecting UAN reduces N immobilization and should provide a higher N concentration within
the restricted application zone. Increased N concentration from broadcasting higher N rates has been reported
to delay cotton maturity and reduce yields (Boquet et
al., 1994; Hutchinson et al., 1995; Maples and Keogh,
1971; McConnell et al., 1993; McConnell et al., 1995).
Crop maturity is a critical production consideration
for cotton producers along the northern edge of the
U.S. Cotton Belt (Gwathmey and Howard, 1998). Practices that delay maturity often reduce yields because
of reduced heat-unit (DD60) accumulation during the
latter part of the growing season. For instance, crop
maturity of cotton produced on the Lexington silt loam
was reduced both years by injecting the N. The accumulated DD60s between planting and first harvest were
2195 and 2190 for 1996 and 1997, respectively. In 1996,
a total of 27 DD60s were accumulated between first
and second harvest periods. In 1997, only one DD60 was
accumulated between first and second harvest periods.
Heat-unit accumulation for the three soils was similar,
and data for the remaining two are not reported. Limited heat-unit accumulation in this region indicates the
need to identify treatments that are conducive to earliness. However, treatments that delay cotton maturity
and promote higher second-harvest yields may be desirable for producers in areas having a greater heat-unit
accumulation potential after first harvest.
CONCLUSIONS
Broadcasting N as AN was a satisfactory application
method for NT cotton production on three loess-derived
soils having different winter covers. Lint yields were
maximized by applying 67 kg N ha21 on the Loring and
Lexington silt loams but 101 kg N ha21 was required to
maximize yields on the Memphis silt loam. Lint yields
were greater in 1 of 8 site-years from broadcasting AN
compared with injecting UAN. Split N applications of
AN resulted in higher yields in only 1 of 8 site-years
relative to broadcasting AN at planting. The extra time
and expense of the split N applications or injecting N
do not justify the added time and expense for cotton
production on these soils. Crop earliness (maturity) was
improved from 79.0 to 82.7% first-harvest on average,
across the 8 site-years by broadcasting N compared with
injection. This may improve the likelihood that cotton
can be harvested before a killing frost along the northern
edge of the U.S. Cotton Belt.
ACKNOWLEDGMENTS
The authors acknowledge the cooperation of the Ames
Plantation staff under terms of a perpetual trust to the University of Tennessee by Julia C. Ames. We also acknowledge the
staff members located at the Milan Experiment Station, Milan,
TN, and the West Tennessee Experiment Station, Jackson,
TN, for their cooperation and efforts in this research.
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