LATITUDE: 36, 7.1844, N
LONGITUDE: 97, 5.3190, W

Annual Rainfall: 33 inches per year (825 mm)
Mean Annual Temp: 59F, 15.5C
Kirkland silt loam (fine, mixed, thermic Udertic Paleustolls)

Publications

1991	Nitrate N and Phosphate-P Concentration in Winter Wheat at Varying Growth Stages. J. Plant. Nutr. 14:267-281.
1993	Use of Stability Analysis for Long-Term Soil Fertility Experiments. Agron J. 85:159-167
1998	Effect of Long-Term N fertilization on Soil Organic C and total N in continuous Wheat Under Conventional Tillage in Oklahoma. Soil and Tillage Res. 47:323-330.
2003	Parham, J.A., S.P. Deng, H.N. Da, H.Y. Sun, and W.R. Raun. 2003. Long-term cattle manure application in soil: II. Effect on soil microbial populations and community structure. Biol and Fertility of Soils. 38:209-215.
2003	Nitrogen Balance in the Magruder Plots Following 109 Years in Continuous Winter Wheat J. Plant Nutr. 26:1561-1580. (pdf)
2004	Sun, H.Y., S.P. Deng, and W.R. Raun. 2004. Bacterial community structure and diversity in a century-old manure-treated agroecosystem. Appl. Environ. Micro. 70:5868-5874.
2007	The Magruder Plots, Untangling the Puzzle. (Agron J. 1191-1198)
2016	Effect of Fertilizer Nitrogen (N) on Soil Organic Carbon, Total N and Soil pH in Long-Term Continuous Winter Wheat (Triticum aestivum L.). Commun. Soil Sci. Plant Anal. DOI: 10.1080/0010364.2016.1147047.
2017	Effect of Long-term Beef Manure Application on Soil Test Phosphorus, Organic Carbon and Winter Wheat Yield. J. Plant Nutr. doi: 10.1080/01904167.2016.1264423
2017	Can Yield Goals Be Predicted? Agron. J.

The Magruder Plots:
Environmental Production History 1892-present

In 1892, A.C. Magruder initiated a soil fertility experiment which would be continued for more than 100 years. The Magruder plots were initially established to evaluate wheat production on native prairie soils without fertilization. Although several changes have been made to the initial trial, the Magruder plots remain the oldest continuous soil fertility wheat experiment west of the Mississippi River. One of the key findings of the Magruder Plots has been the sustained wheat production of more than 16 bu/ac, following more than 100 years without any fertilization. Not until the last 5-10 years have we seen any benefit of K fertilization. Early on, the response to P fertilization was notable (P-only versus the check). As issues of sustainability and environmental safety become increasingly more important, trials such as the Magruder Plots will be further explored.

Procedures

Initially only one plot was established to evaluate native wheat production without the application of organic or inorganic fertilizers from 1893 to 1898. From 1899 to 1929, half of the experimental area was fertilized with barnyard manure while the other half received no fertilization. In 1930, Dr. H.J. Harper established ten separate fertilization treatments on these plots which would continue to 1947. Due to a university construction decision for a new dormitory, plots from six of the ten treatments were moved (surface 0- 16") following wheat harvest in 1947 to its present location on the Agronomy Research Station (Figure 1). The subsoil at the new location was noted to be very similar to that of the original site located just west of present day Stout Hall.

Table 1. Changes in location and treatment modifications for Magruder plots,1892-present.

Year	Trts.	Nitrogen source	N rate, lb. N/ac	N rate, manure lb. N/ac	P source	Row spacing inches	Seed Rate lb/ac	Loc.	Seed Type
1892-1898	1	-	-	-	-	7	75	Old	SRWW
1899-1912	2	Manure only	-	-	-	7	75	Old	SRWW
1913-1929	2	Manure only	-	120^**	-	7	75	Old	HRWW
1930-1933	10	NaNO₃(16-0-0)	33	120^**	OSP (0-20-0-12S)	7	75	Old	HRWW
1934-1945	10	NaNO ₃(16-0-0)	33	120^**	OSP (0-20-0-12S)	14	50	Old	HRWW
1946-1947	10	NH₄NO₃(33.5-0-0)	33	120^**	OSP (0-20-0-12S)	14	50	Old	HRWW
1948	6	NH₄NO₃(33.5-0-0)	33	120^**	OSP (0-20-0-12S)	7	75	New	HRWW
1949-1957	6	NH₄NO₃(33.5-0-0)	33	120^**	OSP (0-20-0-12S)	14	50	New	HRWW
1958-1967	6	NH₄NO₃(33.5-0-0)	33	120^**	OSP (0-20-0-12S)	10	60	New	HRWW
1968-1993	6	NH₄NO₃(33.5-0-0)	60	240^**	TSP (0-46-0)	10	60	New	HRWW
1994-pres	6	NH₄NO₃(33.5-0-0)	60	240^**	TSP (0-46-0)	7.5	60	New	HRWW

Table 2. Soil fertility treatment effects on Magruder Plot wheat grain yields, Stillwater, OK, 1930-2004

	Treatment N-P₂O₅ K₂O lb/ac/yr			1930-37	1938-47	1948-57	1958-67	1968-77	1978-87	1988-97	1998-04
1. Manure only +				24.1	17.5	18.0	29.9	30.2	34.1	28.0	39.5
2.	0	0	0	16.6	9.5	13.3	18.9	18.0	19.6	15.1	18.6
3.	0	30	0	21.2	15.9	19.1	21.5	18.8	22.4	14.7	20.4
4.	33^*	30	0	22.6	17.2	19.8	31.7	36.0	30.5	27.4	41.7
5.	33^*	30	30	23.4	17.4	19.9	29.4	33.9	30.9	32.4	44.6
6.	33^*	30	30+ lime	22.3	17.3	22.5	33.0	37.6	33.0	32.9	45.6

Mean				21.7	15.8	18.8	27.4	28.9	28.4	25.1	35.1
SED				2.6	1.8	1.8	2.0	2.6	1.9	2.6	3.7
* N rate increased to 60 lbs N/ac in 1968. + Beef manure applied at a rate of 120 and 240 lb N/ac every fourth year for periods 1930-1967 and 1967-present, respectively. Lime (L) applied when soil analysis indicated a pH of 5.5 or less.