Residual Effects of Phosphorus Fertilizer in an Irrigated Rotation in the Southwest
1963
Leamer, Ross W.
Response to phosphorus fertilizer on a phosphorus-deficient Reddish-Brown soil was measured through 8 years. Yields, percent P in plant, and NaHCO₃-extractable soil P were followed through 2 cycles of alfalfa and 2 intervening crops of sorghum. Increased yields were obtained until P equal to the application was removed in harvested crops. Alfalfa yields were closely correlated with both percent P in hay and NaHCO₃-extractable soil P during the first 4 years. High yields were maintained in the second cycle of the rotation, but percent P in hay and NaHCO₃-extractable soil P were at levels associated with low yields during the first cycle. Sorghum following alfalfa was not affected by N fertilizer. Second-year sorghum benefited from N only where there was ample P.
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