Experiment 803, Long-Term Application of K in Winter Wheat under Acid Soil Conditions, Haskell, OK

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.