Improved Corrective Fertilizer Recommendations Based on a Two‐Step Alternative Usage of Soil Tests: I. Recovery of Soil‐Equilibrated Phosphorus

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Abstract
The objective of these studies was to improve corrective fertilizer P recommendations using soil quicktest methodology which measures P‐fixation (buffering) tendencies of individual soils. Actual amounts of fertilizer P required to reach a selected sufficiency level of Bray‐1 available P were measured from the added P vs. available P relationship in 10 soils with a wide range in P‐fixation tendency. The new (universal) extractant of Mehlich was found to give approximately the same indication of P fixation as did Bray‐1, indicating that both P and K may be equilibrated together thereby eliminating one extraction. Regression analyses were made between the actual and variously computed amounts of P to reach sufficiency level based on constant fraction recovery, quicktest measured recovery (one‐step), and regression‐adjusted recovery (two‐step). This showed that most of the deviations between actual and computed values can be eliminated by this quicktest‐computed, regression‐adjusted procedure. Hence fertilizer recommendations evidently can be improved correspondingly. Relatively low correlation of Bray‐1 available P with yields of corn seedlings in this preliminary study appeared to be not the fault of the soil test but the effect of plant exploitation of the small aliquots of soils used.