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The Magruder Plots: Untangling the Puzzle

Previously Published in Agron. J. 99:1191–1198 (2007)

Dep. of Plant and Soil Sciences, Oklahoma State Univ., Stillwater, OK 74078. Contribution from the Oklahoma Agricultural Experiment Station

View larger version (15K): [in this window] [in a new window]   Fig. 1. Monthly average temperature and rainfall (summed over days of the month) averaged over 36 (1969–2006) years at the Agronomy Research Station, Stillwater, OK.

View larger version (80K): [in this window] [in a new window]   Fig. 2. The Magruder Plots at their current location at the Agronomy Research Station, Stillwater, OK. The experiment was initiated in 1892 and has been repository of scientific information.

View larger version (15K): [in this window] [in a new window]   Fig. 3. Winter wheat grain yield averaged over several years based on treatment response in selected time periods for each of the treatments. Each period denotes average yield with similar yield response due to treatments (Modified from Boman et al., 1996).

View larger version (24K): [in this window] [in a new window]   Fig. 4. Winter wheat grain yield by variety in the Magruder Plots, Stillwater, OK. Cultivars Fultz, Currell, SNG, Kharkov, Turkey, Tenmarq, Pawnee, Ponca, Concho, Kaw, Scout66, Triumph6, Osage, Tam101, Karl, Tonkawa, Custer, and Endurance were planted in 1893 and 1895–1907, 1894, 1908–1911, 1912–1916, 1917–1942, 1943–1945, 1946–1953, 1954–1957, 1958–1963, 1964–1968, 1969–1973, 1974–1977, 1978–1979, 1980–1992, 1993–1994, 1995–1999, 2000–2005, and 2006, respectively.

View larger version (13K): [in this window] [in a new window]   Fig. 5. Effect of applied N, P, K, and lime in the Magruder Plots for three selected time periods (1930–1957, 1958–1994, and 1995–2006).

View larger version (12K): [in this window] [in a new window]   Fig. 6. Regression lines of stability (winter wheat grain yield vs. environment mean) for all treatments at the Magruder Plots, Stillwater, OK, for data compiled over 76 yr (Modified from Raun et al., 1993). NPKL = superphosphate + sodium nitrate + potash + lime.

View larger version (6K): [in this window] [in a new window]   Fig. 7. Decrease in soil organic matter [OM = organic C x 1.8 + 0.35 (Ranney, 1969)] for data gathered in selected years in the Magruder Plots, Stillwater, OK (Raun, 2006).

View larger version (9K): [in this window] [in a new window]   Fig. 8. Effect of treatments on the lower internode discoloration (indicator of the abundance of soilborne disease causing organisms other than Pythium spp.) and Pythium spp. infection in the Magruder Plots in 1993, Stillwater, OK (modified from Boman et al., 1996).