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Long-Term Effects of Tillage, Nitrogen, and Rainfall on Winter Wheat Yields in the Pacific Northwest

^a USDA–Natural Resources Conservation Service, 820 Bay Ave., Suite 107, Capitola, CA 95010
^b Texas A&M Univ. System, Texas Agric. Exp. Stn., 6500 Amarillo Boulevard West, Amarillo, TX 79106
^c USDA-ARS Columbia Plateau Conservation Res. Center, 48037 Tubbs Ranch Rd., Adams, OR 97810

View larger version (32K): [in a new window]   Fig. 1. The influence of tillage on winter wheat for the four major time periods of the tillage/fertility experiment at Pendleton, OR, 1945–1997. Values without a letter in common are significantly different at the 0.05 probability level, according to Tukey's HSD.

View larger version (22K): [in a new window]   Fig. 2. The influence of N fertilization during (a) Period 1 (1944–1951); (b) Period 2 (1952–1961); (c) Period 3 (1962–1987); and (d) Period 4 (1988–1997) on winter wheat for the tillage/fertility experiment at Pendleton, OR, 1945–1997.

View larger version (23K): [in a new window]   Fig. 3. Long-term response of soft white winter wheat to N fertilization for Period 3 (1962–1987), Period 4 (1988–1997), and pooled data for Periods 3 and 4 (1962–1997) for the tillage/fertility experiment at Pendleton, OR, 1945–1997.

View larger version (20K): [in a new window]   Fig. 4. The influence of (a) annual precipitation, and (b) 9-month cropping season (1 October–30 June) precipitation on winter wheat for the tillage/fertility experiment at Pendleton, OR, 1945–1997.

View larger version (31K): [in a new window]   Fig. 5. The influence of soil depth and 9-mo cropping season (1 October–30 June) precipitation on winter wheat yield, during Period 3 (1962–1987), for the tillage/fertility experiment at Pendleton, OR, 1945–1997. Points represent the mean yield of individual plots. The bars indicate ±1 SE. Curves were generated using distance-weighted least squares.

View larger version (33K): [in a new window]   Fig. 6. Five-year moving average of winter wheat yields for the tillage/fertility experiment at Pendleton, OR, 1945–1997.