Experiment 801: Wheat Grain Yield Response to NPK under Acid Soil Conditions, Haskell, OK
Abstract

Many of the soils where winter wheat is grown in northeastern Oklahoma are extremely acid and deficient in phosphorus.  Experiment 801 was established in the fall of 1977 to evaluate the long-term effects of nitrogen, phosphorus and potassium fertilizer applications in continuous winter wheat grown on an acid soil.  Applied P was expected to precipitate some of the Al in soil solution, especially at the low soil pH levels where increased Al was expected at this site.  Applied P without N produced the highest grain yields from 1978 to 1987, and 1988 to 1997.  Following two consecutive years of applied lime (2240 kg/ha, 71% ECCE) to the entire area, the highest yielding plots were those receiving both N and P.  The lowest yielding plots were those receiving only N.  In general, those plots with the highest yields had the lowest grain %N at this site.  This suggests that yield maximums were not achieved since increased grain %N has been found at N rates in excess of that required for maximum yields.

Materials and Methods

Experiment 801 was established in the fall of 1977 under conventional tillage on a Taloka silt loam (fine-mixed, thermic Mollic Albaqualf).  This trial along with 802, 803, and 804 was initiated by Dr. Robert L. Westerman, Professor and Head of the Department of Plant and Soil Sciences.  Wheat has been planted for 19 continuous years in 10 inch rows at seeding rates of 90 pounds per acre (rates increased when  planting was delayed).  Fertilization, planting and management dates are listed in Table 1. The experimental design in this continuing experiment employs  a randomized complete block with four replications.  Fertilizer treatments and average grain yields for selected periods are reported in Table 2. Individual plots at this site are 17 feet wide and 50 feet long.  The center 10 feet are harvested with a conventional combine the entire 50 feet in length.  In addition to wheat grain yield measured every year, periodic soil and grain samples were taken for chemical analyses.  Results from surface (0-6 inches) soil samples collected in 1995 are reported in Table 3.

Results

Soil pH declined significantly in all plots receiving N (with or without P and K).  As a result, low soil pH (increased Al and Mn in soil solution) is the controlling factor for wheat grain production at this site.  The lowest soil pH values were also those associated with the highest NO3-N levels in the surface.  Applied P was expected to precipitate some of the Al in soil solution, especially at low soil pH levels where increased Al was expected.  Applied P without N produced the highest grain yields from 1978 to 1987, and 1988 to 1997.  Applied N did not result in any increased yield with or without P in the first twenty years of the experiment.  However, following two consecutive years of applied lime (2240 kg lime/ha, 71% ECCE), the combined application of N and P has resulted in the highest yields.  It was interesting to find NO3-N levels in excess of 300 ppm in the surface six inches.  This translates into over 600 lb N /ac that would be available.  Over the 18 years from the time the experiment was initiated to being soil sampled in 1995, accumulation of N was expected.  However, if leaching of excess N were a viable pathway over time, surface accumulation at levels greater than the annual rate applied would likely not be found.  Increased applied K (treatments 6, 7 and 8) tended to increase surface NO3-N.

Table 1.  Treatment applications and experimental management for continuous winter wheat Experiment 801, Haskell, OK, 1978-2000.

Year

Variety

Fertilizer Application Date

Planting Date

Harvest Date

Seeding Rate, lb/ac

 

1978

 

 

 

6-26-78

75

1979

Osage

10-15-78

10-24-78

7-2-79

100

1980

TAM W-101

10-15-79

10-17-79

6-30-80

120

1981

TAM W-101

10-8-80

10-14-80

6-24-81

90

1982

TAM W-101

10-28-81

10-30-81

7-16-82

90

1983

TAM W-101

9-9-82

9-29-82

7-5-83

90

1984

Vona

11-4-83

11-4-83

6-20-84

90

1985

Vona

10-3-84

10-8-84

6-18-85

90

1986

Vona

1-10-86

1-11-86

6-19-86

150

1987

Chisholm

9-22-86

9-23-86

6-17-87

90

1988

Chisholm

10-2-87

10-6-87

6-9-88

90

1989

Chisholm

10-13-88

10-14-88

6-20-89

90

1990

Chisholm

10-12-89

10-18-89

6-13-90

90

1991

Chisholm

8-21-90

10-15-90

6-20-91

90

1992

Chisholm

10-1-91

10-2-91

6-20-92

90

1993

Karl

10-5-92

10-6-92

6-18-93

120

1994

2163

10-5-93

10-6-93

6-15-94

90

1995

Tonkawa

10-10-94

10-12-94

6-17-95

90

1996

Tonkawa

10-6-95

10-12-95

6-18-96

90

1997

Tonkawa

10-9-96

10-11-96

6-18-97

100

1998-L

2163

10-2-97

10-3-97

6-18-98

90

1999-L

2137

9-30-98

10-14-98

7-6-99

110

2000

2137

9-29-99

10-8-99

6-2-00

95

L lime applied at a rate of 2240 kg/ha (1 ton/acre) in July 1998 (71% ECCE)
L lime applied at a rate of 2240 kg/ha (1 ton/acre) in July 1999 (71% ECCE)

Table 2.  Treatment structure and wheat grain yields of long-term wheat Experiment 801, Haskell, OK, 1978-1997.

Trt.

N

P2O5

K2O

1978-87

1988-97

1998-00

1978-2000

 

lb/ac

 

bu/ac

%N

bu/ac

%N

bu/ac

bu/ac

%N

1.

0

0

0

18.2

2.52

17.6

2.65

22.7

18.6

2.55

2.

0

120

120

34.9

2.07

29.8

2.67

27.9

31.8

2.20

3.

100

0

0

14.8

2.61

1.4

2.93

6.8

7.9

2.68

4

150

0

0

15.3

2.63

0.0

2.83

3.7

7.2

2.66

5.

100

120

0

27.7

2.50

14.2

3.06

24.8

21.5

2.60

6.

100

120

40

31.5

2.47

20.4

2.72

29.8

26.5

2.52

7.

100

120

80

30.2

2.57

20.7

2.76

27.2

25.7

2.60

8.

100

120

120

30.5

2.52

16.5

2.91

29.7

24.3

2.59

9.

100

0

120

16.0

2.57

1.1

3.15

5.7

8.3

2.68

10.

100

40

120

30.4

2.45

5.8

2.81

24.7

19.0

2.52

11.

100

80

120

34.2

2.49

15.6

2.75

30.7

25.7

2.55

12.

150

120

120

29.3

2.63

8.6

2.97

16.1

18.6

2.70

13.

150*

120

120

28.3

2.60

7.8

2.40

14.6

17.6

2.56

SED

 

 

 

2.9

0.11

3.2

0.22

3.6

3.4

0.15

CV, %

 

 

 

16

6

37

11

25

24

8

*-N split applied, 100 lb N/ac in the fall and 50 lb N/ac in the spring. N applied as 34-0-0, P as 0-46-0, and K as 0-0-60. SED - standard error of the difference between two equally replicated means. CV - coefficient of variation.

Table 3.  Treatment structure of long-term wheat Experiment 801 and surface (0-6 inches) soil test analyses from samples collected in 1995, Haskell, OK.

Trt.

N

P2O5

K2O

pH

NO3-N

P

K

Total N

Organic C

 

 

lb/ac

 

 

ppm

ppm

ppm

%

%

 

 

 

 

 

 

 

 

 

 

1.

0

0

0

5.32

1.6

8

163

0.069

0.741

2.

0

120

120

5.15

3.4

71

302

0.075

0.817

3.

100

0

0

4.17

300.6

13

118

0.110

0.748

4

150

0

0

4.18

312.2

32

199

0.141

0.724

5.

100

120

0

4.65

66.5

62

147

0.086

0.794

6.

100

120

40

4.80

11.7

88

157

0.087

0.839

7.

100

120

80

4.67

31.7

82

193

0.083

0.800

8.

100

120

120

4.43

64.6

92

334

0.091

0.801

9.

100

0

120

4.21

311.7

15

385

0.111

0.707

10.

100

40

120

4.15

203.4

31

359

0.104

0.771

11.

100

80

120

4.46

59.4

59

265

0.087

0.815

12.

150

120

120

4.19

205.4

95

326

0.108

0.812

13.

150*

120

120

4.07

321.8

86

308

0.131

0.806

SED

 

 

 

0.22

59

11

46

0.010

0.030

CV, %

 

 

 

7

58

27

26

15

5

*-N split applied, 100 lb N/ac in the Fall and 50 lb N/ac in the Spring. N applied as 34-0-0, P as 0-46-0, and K as 0-0-60. SED - standard of the difference between two equally replicated means. CV - coefficient of variation.