Residual Effects of Phosphorus Fertilizer on an Eastern Oregon Soil
1961
Hunter, Albert S. | Hoffman, E. N. | Yungen, John A.
In each of three successive years a 6-year rotation (barley-3 years alfalfa-corn-sugar beets) was established on separate plots of Owyhee silt loam treated with 0, 26, 53, 105, and 210 pounds of P per acre and a uniform rate of N. Plots were split in the fifth year for differential N and in the sixth year for P and N treatments. Yields and removal of P by crops were determined each year. In the sixth year measurements of soluble P in soil, percent P in plant derived from soil P, A-values, and yield and compositional responses of sugar beets to added P fertilizer were employed to evaluate levels of available residual P in soil. All methods of evaluation indicate that 210 pounds of P were adequate for all crops in the 6-year rotation. Residual P from the 105-pound rate was inadequate for maximum yield of beets. Essentially no residual P remained in the sixth year from the 26- and 53-pound applications. Accumulation of N by alfalfa was unaffected by initial rate of P. Fertilizer N substantially increased corn yields following 3 years of productive alfalfa.
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