Experiment 803: Wheat Grain Yield Response in Acid Soils to Potassium Applications, Haskell, OK

Abstract

Soils in northeastern Oklahoma are generally acid where winter wheat is grown.  Experiment 803 was established to evaluate potassium fertilizer applications at fixed rates of nitrogen and phosphorus on long-term wheat grain yields.  No response to applied K has been observed in this experiment from the one-time K applications in 1977.  In general, applied K has had little impact on grain %N.  However, in the last two years there has been a trend for applied K to increase grain %N.  Soil pH has decreased in this experiment since 1977 and may well be controlling response since all plots are now below 4.7.  Soil total N and organic C have largely been unaffected by K fertilization. 

Materials and Methods

Experiment 803 was established in the fall of 1977 under conventional tillage on a Taloka silt loam (fine-mixed, thermic Mollic Albaqualf).  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 used in this experiment along with 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 further chemical analyses.  Results from surface (0-6 inches) soil samples collected in 1995 are reported in Table 3.

Results

Since 1978 no response to the one-time application of applied K has been observed in any year, or over the time periods reported in Table 2.  Yield levels were higher in the first ten years of the experiment.  Decreased yields with time can be attributed to increased soil acidity that has been measured with time.   Soil test K levels were below 80% sufficiency in the check plot (treatment 1, Table 3) by 1994, yet no yield differences have been observed when compared to the high K rate treatments.  Soil pH has decreased in this experiment since 1977 and may well be controlling response since all plots are now below 4.7.  Soil total N and organic C have largely been unaffected by K fertilization.

Table 1.  Treatment applications and experimental management for continuous winter wheat Experiment 803, 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

6-25-81

90

1982

TAM W-101

10-27-81

10-30-81

7-19-82

90

1983

TAM W-101

9-9-82

9-29-82

7-6-83

90

1984

Vona

11-4-83

11-4-83

6-21-84

90

1985

Vona

10-3-84

10-8-84

6-18-85

90

1986

Vona

10-10-85

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

10-15-90

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

2163

10-2-97

10-3-97

6-18-98

90

1999

2137

9-30-98

10-14-98

7-7-99

110

2000*

2137

9-29-99

10-8-99

 

95

* No harvest due to rye grass problem


Table 2.  Treatment structure and wheat grain yields of long-term wheat Experiment 803, Haskell, OK, 1978-1999.

Trt.

N

P2O5

K2O

1978-87

1988-97

1998-99

1978-1999

 

lb/ac

bu/ac

%N

bu/ac

%N

bu/ac

%N

bu/ac

%N

1.

100

100

0

28.8

2.59

21.7

2.68

8.9

2.67

23.9

2.61

2.

100

100

60

29.9

2.59

21.7

2.53

10.9

2.69

24.6

2.59

3.

100

100

120

30.6

2.62

25.1

2.57

12.9

2.69

26.7

2.62

4

100

100

240

29.5

2.67

23.2

2.61

9.8

2.71

25.0

2.66

5.

100

100

600

30.1

2.64

21.3

2.55

10.8

2.75

24.5

2.65

6.

100

100

1200

28.9

2.64

18.7

2.61

10.1

2.84

22.8

2.66

SED

 

 

 

2.7

0.13

3.1

0.06

1.8

0.07

3.0

0.11

CV, %

 

 

 

13

7

20

3

24

4

17

6

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 winter wheat Experiment 803 and surface (0-6 inches) soil test analyses from 1994, Haskell, OK, 1978-1999.

Trt.

N

P2O5

K2O

pH

NO3-N

P

K

Total N

Organic C

 

 

lb/ac

 

 

ppm

ppm

ppm

%

%

1.

100

100

0

4.58

14.0

76

66

0.079

0.969

2.

100

100

60

4.65

13.6

74

83

0.081

0.967

3.

100

100

120

4.73

14.2

85

89

0.084

0.991

4

100

100

240

4.68

16.8

74

78

0.083

0.969

5.

100

100

600

4.70

15.8

69

116

0.083

0.992

6.

100

100

1200

4.65

14.6

81

161

0.080

0.983

SED

 

 

 

0.07

2.0

7.4

17

0.002

0.030

CV, %

 

 

 

2

19

14

25

4

4

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.