Experiment 407: Wheat Grain Yield Response to Nitrogen, Phosphorus and Potassium Fertilization (Dryland)
Experiment 407 Plot Plan

Experiment 407 Plot Plan


Abstract

Winter wheat grain yield response to fertilization with nitrogen (N), phosphorus (P) and potassium (K) in long-term experiments continues to be relevant in terms of sustainability and environmental risk.  Experiment 407 was established in 1966 and has now been conducted for 34 years.  Response to applied N, P, and K has been limited at this site, largely due to high soil test nutrient levels and low yields over the extensive number of years evaluated.   From 1966 to 1980, only limited increases in grain yield due to applied N were observed.  Since 1980, grain yields have increased significantly due to applied N, generally being maximized at the 40 lb N/ac/yr rate.  Yield increases due to applied N in this dryland winter wheat experiment have ranged from 5 to 10 bu/ac.  Grain %N levels have been found to increase linearly up to 80 lb N/ac/yr (beyond the N rate required for maximum yields).  As grain protein premiums become increasingly more important, optimum N rates for grain %N will need to be refined.

Materials and Methods

In the fall of 1965, Experiment 407 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 for 31 continuous years in 10 inch rows at seeding rates of 60 pounds per acre.   Grain yield data for the 1971 crop year was lost due to drought.  The experimental design employed is a randomized complete block with six replications. Variety changes and associated fertilizer application, planting and harvest dates are included in Table 1.  Fertilizer treatments used in this experiment and grain yield averages from selected periods are reported in Table 2. Individual plots at this site are 15 feet wide and 60 feet long.  The center 10 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.  Soil test results from surface samples collected in the summer of 1995 are included in Table 3.

Table 1.  Treatment applications, and experimental management for continuous winter wheat Experiment 407, Altus, OK, 1966-2000.

Year

Variety

Fertilizer Application Date

Planting Date

Harvest Date

Seeding Rate lb/ac

Topdress Date

1966

 

 

 

 

 

 

1967

 

 

 

 

 

 

1968

 

 

 

 

 

 

1969

 

 

 

6-3-69

 

 

1970

KAW 61

10-9-69

10-11-69

6-5-70

40

 

1971

KAW 61

10-14-70

10-20-70

6-1-71

60

1-26-71

1972

Danne

8-17-71

10-5-71

6-8-72

40

2-23-72

1973

Nicoma

9-5-72

10-4-72

6-6-73

40

 

1974

Nicoma

9-21-73

10-24-73

6-13-74

50

2-11-74

1975

Nicoma

10-9-74

10-11-74

6-12-75

40

 

1976

Triumph 64

8-14-75

10-7-75

6-10-76

60

1-13-76

1977

Triumph 64

8-10-76

10-14-76

6-8-77

60

2-17-77

1978

Triumph 64

9-14-77

11-7-77

6-22-78

60

3-14-78

1979

Triumph 64

8-20-78

10-9-78

6-20-79

60

3-12-79

1980

Triumph 64

9-12-79

10-18-79

6-19-80

60

3-10-80

1981

TAM W-101

8-20-80

11-7-80

6-10-81

60

1-26-81

1982

TAM W-101

9-8-81

10-27-81

6-30-82

60

2-23-82

1983

TAM W-101

8-18-82

10-28-82

6-16-83

60

3-4-83

1984

TAM W-101

8-25-83

12-5-83*

6-12-84

60

3-2-84

1985

TAM W-101

8-29-84

10-10-84

6-20-85

90

3-5-85

1986

TAM W-101

8-23-85

11-5-85

6-2-86

60

2-19-86

1987

TAM W-101

9-16-86

11-15-86

6-23-87

60

3-5-87

1988

TAM W-101

9-4-87

10-6-87

6-10-88

60

2-18-88

1989

TAM W-101

10-26-88

11-17-88

6-22-89

60

3-9-89

1990

TAM W-101

8-10-89

9-22-89

6-8-90

60

3-9-90

1991

TAM W-101

8-30-90

9-27-90

6-19-91

60

2-7-91

1992

TAM W-101

9-22-91

9-27-91

6-16-92

60

2-9-92

1993

Karl

 

10-20-92

6-16-93

60

3-25-93

1994

Karl

8-17-93

9-28-93

6-3-94

60

3-24-94

1995

Tonkawa

8-19-94

10-27-94

6-17-95

60

3-8-95

1996

Tonkawa

8-18-95

10-11-95

6-6-96

60

2-3-96

1997

Tonkawa

8-15-96

10-1-96

6-14-97

60

2-3-97

1998

Tonkawa

9-19-97

10-3-97

6-4-98

60

3-12-98

1999

Tonkawa

9-9-98

10-12-98

6-7-99

60

1-27-99

2000

Custer

8-24-99

10-8-99

5-24-00

60

3-9-00

N, P and K applied as 34-0-0, 0-46-0 and 0-0-60 respectively.  All N applied in the spring.  P and K applied preplant and incorporated.  SED - standard error of the difference between two equally replicated means, CV - coefficient of variation.

Table 2.  Treatment structure of a long-term supplemental irrigation winter wheat Experiment 407 and overall means, Altus, OK, 1966-2000        

Trt .

N

P2O5

K2O

1966-1970

 

1973-1980

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

19.2

2.88

24.2

2.32

21.3

2.08

15.0

2.37

19.8

2.42

2

20

0

0

18.4

2.90

25.9

2.63

23.9

2.41

19.3

2.60

22.2

2.64

3

40

0

0

17.4

2.96

26.2

2.58

24.3

2.54

20.4

2.83

22.5

2.72

4

80

0

0

18.3

2.97

27.7

2.76

25.3

2.60

22.3

3.00

23.9

2.83

5

0

40

0

22.1

2.74

25.1

2.11

22.7

1.86

15.2

2.41

20.9

2.28

6

20

40

0

19.9

2.94

27.1

2.46

28.2

2.10

20.5

2.46

24.3

2.49

7

40

40

0

16.8

3.00

30.2

2.72

29.4

2.40

22.7

2.71

25.6

2.71

8

80

40

0

15.9

2.98

26.5

2.74

27.6

2.77

25.1

3.02

24.8

2.88

9

0

40

40

21.9

2.71

24.3

2.10

22.5

2.15

15.5

2.36

20.7

2.33

10

20

40

40

21.4

3.01

28.6

2.52

29.6

2.06

19.9

2.49

25.2

2.52

11

40

40

40

17.9

2.93

30.4

2.76

29.5

2.44

23.4

2.66

26.1

2.70

12

80

40

40

15.9

2.93

28.1

2.85

28.1

2.69

24.4

2.91

25.2

2.84

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SED

 

 

 

1.5

0.13

2.4

0.18

2.22

0.34

2.44

0.11

2.29

0.21

CV, %

 

 

 

11

6

13

10

12

20

17

6

14

11

N, P and K applied as 34-0-0, 0-46-0 and 0-0-60 respectively. 1971-1972-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 407, Altus, OK, 1966-1997.

Trt .

N

P2O5

K2O

pH

Organic C

Total N

P

K

 

 

lb/ac

 

 

%

%

ppm

ppm

 

 

 

 

 

 

 

 

 

1

0

0

0

6.8

0.929

0.079

7.4

502

2

20

0

0

6.8

0.989

0.094

8.4

480

3

40

0

0

6.8

0.982

0.084

9.2

546

4

80

0

0

6.5

1.038

0.091

9.2

528

5

0

40

0

6.8

0.948

0.084

42.2

496

6

20

40

0

6.7

0.950

0.082

36.6

525

7

40

40

0

6.7

1.045

0.092

34.1

530

8

80

40

0

6.4

1.087

0.104

33.5

516

9

0

40

40

6.9

0.931

0.081

45.8

590

10

20

40

40

6.8

1.006

0.085

37.3

570

11

40

40

40

6.6

1.024

0.087

33.0

583

12

80

40

40

6.4

1.076

0.095

32.5

564

 

 

 

 

 

 

 

 

 

SED

 

 

 

0.12

0.12

0.004

3.5

84

CV

 

 

 

3

10

8

22

7

N, P and K applied as 34-0-0, 0-46-0 and 0-0-60 respectively.  All N applied in the spring.  P and K applied preplant and incorporated.  SED - standard error of the difference between two equally
replicated means, CV - coefficient of variation.