Fertilizer Needs for Restoring Productivity on Pullman Silty Clay Loam After Various Degrees of Soil Removal

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Abstract
Greenhouse and field studies were conducted on Pullman silty clay loam to assess the relative productivities of its genetic horizons and permissible depth of cut in land leveling. German millet was grown in the greenhouse experiment. Without fertilizer, the 0‐ to 5‐inch horizon produced highest yields. Under high N and P levels, only the 13‐ to 19‐inch depth produced yields lower than the surface soil. The 28‐ to 38‐inch horizon produced yields equivalent to the 0‐ to 5‐inch horizon and greater than all other nonsurface depths studied. Trends in N and P uptake were generally similar to those in dry matter yields.In the field experiment, N was required for maximum yields of grain sorghum on undisturbed soil and on all degrees of cut. Nitrogen and P were required when 4 or more inches of top‐soil was removed and restored yields where up to 12 inches of topsoil was removed. Yields on heavily fertilized 16‐inch cuts were 80% of those on similarly fertilized, undisturbed soil.

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