Experiment 406: Wheat Grain Yield Response to Nitrogen, Phosphorus and Potassium Fertilization under Irrigation
Experiment 406 Plot Plan
experiment 406 Altus, OK

Abstract

Grain yield response of irrigated winter wheat to fertilization with nitrogen (N), phosphorus (P) and potassium (K) in a long-term experiment has not been extensively evaluated.  Experiment 406 was established in 1966 to evaluate fertilizer applications on irrigated winter wheat grown in southwestern Oklahoma.  Following 34 years of continuous wheat, response to applied N, P, and K remains somewhat dynamic.  Over a 34 year period, only applied N has provided consistent wheat yield increases.  Grain yield maximums have been achieved at an average annual N rate of 40 lb N/ac.  However, grain percent N (grain protein) has increased when N was applied at rates greater than 40 lb N/ac.  In the last ten years, soil test P has approached deficient levels and yield response to applied P has been significant over this time period.  Yield response due to applied K has not been observed in this 34 year experiment where soil test K levels were initially high.

Materials and Methods

In the fall of 1965, Experiment 406 was established under conventional tillage on a Tillman-Hollister clay loam (fine-mixed, thermic Typic Paleustoll) at the Irrigation Research Station near Altus, Oklahoma. Winter Wheat has been planted in 10  inch rows at seeding rates of 90 pounds per acre.  In 1969 and 1971, grain yield data was not obtained.  In most years, plots were not irrigated in the spring because the economics of the irrigation district have dictated that water is only released for summer crops.  When water was applied, it was usually a pre-irrigation prior to planting.  The experimental design employed is a randomized complete block with six replications.  Management, varieties, and application dates are reported in Table 1.  Fertilizer treatments used in this experiment and average grain yields over selected periods are reported in Table 2.  Soil test levels from surface samples collected in 1995 are included in Table 3.  Individual plots at this site are 15 feet wide and 60 feet long.  The center 10 (1966-1995) and 6 (1996-present) feet were harvested with a conventional combine the entire 60 feet in length.  In addition to wheat grain yield measured every year, periodic soil and grain samples were taken for further chemical analyses.

Table 1.  Treatment applications and experimental management for continuous winter wheat Experiment 406, Altus, OK, 1966-2000.

Year

Variety

Fertilizer

Planting Date

Harvest Date

Seeding Rate

Irrigation

Topdress

 

 

Application

 

 

lb/ac

Date

Date

 

 

Date

 

 

 

 

 

1966

 

10-1-66

 

 

 

 

2-9-67

1967

 

 

 

 

 

 

 

1968

 

 

 

 

 

 

 

1969

 

 

 

 

 

4-28-69

1-28-69

1970

Tascosa

10-10-69

10-11-69

6-6-70

90

2-17-70

2-2-70

1971*

Tascosa

10-14-70

10-21-71

6-1-71

90

8-27-70

1-25-71

1972

Sturdy

8-17-71

10-9-71

6-8-72

90

None

2-21-72

1973

TAM W-101

9-11-72

10-12-72

6-11-73

90

9-13-72

 

1974

TAM W-101

8-31-73

10-26-73

6-13-74

90

None

2-11-74

1975

TAM W-101

9-5-74

9-6-74

6-13-75

90

8-2-74

 

1976

TAM W-101

8-20-75

10-9-75

6-8-76

90

9-3-75

1-13-76

1977

TAM W-101

8-9-76

10-14-76

6-9-77

80

8-11-76

2-16-77

1978

TAM W-101

9-14-77

10-31-77

6-23-78

90

None

3-13-78

1979

TAM W-101

8-20-78

10-10-78

6-20-79

90

None

3-13-79

1980

TAM W-101

9-13-79

10-18-79

6-13-80

96

None

3-7-80

1981

TAM W-101

8-22-80

11-7-80

6-10-81

90

None

1-26-81

1982

TAM W-101

9-9-81

10-27-81

6-30-82

90

None

2-23-82

1983

TAM W-101

8-16-82

8-16-82

6-15-83

90

None

3-2-83

1984

TAM W-101

8-25-83

11-3-83

6-13-84

90

None

3-1-84

1985

TAM W-101

8-29-84

10-10-84

6-20-85

90

9-7-84

3-14-85

1986

TAM W-101

8-23-85

11-4-85

6-10-86

90

None

2-18-86

1987

TAM W-101

9-18-86

11-15-86

6-8-87

90

None

3-6-87

1988

TAM W-101

9-1-87

10-6-87

6-9-88

90

9-2-87

2-17-88

1989

TAM W-101

10-24-88

11-17-88

6-22-89

90

9-1-88

All N preplant

1990

TAM W-101

8-10-89

9-22-89

6-9-90

90

8-24-89

All N preplant

1991

TAM W-101

8-30-90

10-10-90

6-18-91

90

None

All N preplant

1992

TAM-W-101

9-22-91

9-27-91

6-15-92

90

7-25,8-8-91

2-9-92

1993

Karl

 

10-20-92

6-15-93

90

8-12-92

3-25-93

1994

Karl

8-17-93

9-28-93

6-3-94

90

8-20-93

3-24-94

1995

Tonkawa

8-19-94

10-27-94

6-17-95

90

8-9-94

3-8-95

1996

Tonkawa

8-17-95

10-12-95

6-5-96

90

None

2-3-96

1997

Tonkawa

8-15-96

10-1-96

6-14-97

90

8-1-96

2-3-97

1998

Tonkawa

9-19-97

10-3-97

6-4-98

90

8-12-97

3-12-98

1999

Tonkawa

9-9-98

10-12-98

6-7-99

90

7-21,8-14-98

1-27-99

2000

Custer

8-24-99

10-8-99

5-24-00

90

8-5-99

3-9-00

*crop loss due to drought.

Table 2.  Treatment structure of a long-term supplemental irrigation winter wheat Experiment 406 and overall means, Altus, OK, 1966-2000.

Trt.

N

P2O5

K2O

1966-1970

1972-1980

1981-1990

1991-2000

1966-2000

 

 

lb/ac

 

bu/ac

%N

bu/ac

%N

bu/ac

%N

bu/ac

%N

bu/ac

%N

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1

0

0

0

14.1

2.47

23.1

2.37

21.3

2.04

13.5

2.53

18.6

2.35

2

40

0

0

19.8

2.57

31.5

2.65

27.4

2.40

20.5

2.68

25.5

2.57

3

80

0

0

18.8

2.82

32.1

2.83

27.6

2.53

21.9

2.95

26.0

2.77

4

120

0

0

18.6

2.95

33.7

2.91

26.7

2.64

22.2

3.02

26.3

2.88

5

160

0

0

17.5

2.97

32.9

3.07

27.3

2.58

23.0

3.08

26.3

2.92

6

40

40

0

22.3

2.54

33.4

2.63

29.6

2.10

21.6

2.58

27.3

2.46

7

80

40

0

18.6

2.91

34.6

2.83

28.9

2.63

25.2

2.93

28.1

2.82

8

120

40

0

17.6

2.96

34.8

2.90

29.1

2.68

27.7

3.06

28.9

2.90

9

160

40

0

16.6

3.19

31.9

2.97

28.7

2.92

26.0

3.11

27.3

3.05

10

40

40

40

20.9

2.64

32.7

2.48

29.3

2.16

21.5

2.61

26.9

2.47

11

80

40

40

19.5

2.82

35.4

2.78

29.8

2.59

24.7

2.91

28.5

2.77

12

120

40

40

15.9

2.88

32.1

2.96

28.3

2.76

26.0

3.10

27.1

2.91

13

160

40

40

15.0

3.00

31.6

3.04

27.3

2.74

24.8

3.08

26.2

2.96

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SED

 

 

 

2.37

0.23

3.24

0.19

3.24

0.21

2.47

0.11

2.9

0.20

CV, %

 

 

 

18

12

14

10

17

12

15

5

16

10

N, P and K applied as 34-0-0, 0-46-0 and 0-0-60 respectively.  N applied 1/2 fall, 1/2 spring
1971-crop loss due to drought.


Table 3.  Treatment structure and surface (0-6 inches) soil test analyses from samples collected in the summer of 1995, Experiment 406, Altus, OK.

Trt .

N

P2O5

K2O

pH

Organic C

Total N

P

K

 

 

lb/ac

 

 

%

%

ppm

ppm

 

 

 

 

 

 

 

 

 

1

0

0

0

7.29

0.84

0.073

9

409

2

40

0

0

7.22

0.88

0.078

9

414

3

80

0

0

7.39

0.90

0.079

7

403

4

120

0

0

7.97

0.90

0.082

8

421

5

160

0

0

7.39

0.90

0.086

9

415

6

40

40

0

7.42

0.87

0.080

31

418

7

80

40

0

7.35

0.93

0.083

26

410

8

120

40

0

7.30

1.00

0.089

27

408

9

160

40

0

7.20

0.96

0.088

27

407

10

40

40

40

7.12

0.87

0.076

32

444

11

80

40

40

7.38

0.93

0.082

25

432

12

120

40

40

7.12

0.95

0.085

24

445

13

160

40

40

6.79

0.93

0.083

24

441

 

 

 

 

 

 

 

 

 

SED

 

 

0.18

0.03

0.004

2.3

14

 

CV, %

 

 

4

6

9

20

5

 

N, P and K applied as 34-0-0, 0-46-0 and 0-0-60 respectively.  N applied 1/2 fall, 1/2 spring. 
SED - standard error of the difference between two equally replicated means, CV - coefficient of variation.