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Improved Corrective Fertilizer Recommendations Based on a Two-Step Alternative Usage of Soil Tests: II. Recovery of Soil-Equilibrated Potassium¹

ABSTRACT

The objective of these studies was to improve corrective fertilizer K recommendations using soil quicktest methodology which measures K-fixation tendencies for individual soils. Actual amounts of fertilizer K required to reach a computed sufficiency level of NH₄OAc-exchangeable K were measured from the added K vs. exchangeable-K relationship in 15 soils with a wide range in K-fixation tendency. Using quicktest procedures, the new Mehlich extractant removed from the various K-equilibrated soils the same amounts of K as did NH₄OAc solution, which suggests the possibility that both K and P may be simultaneously equilibrated and extracted with one extractant. Regressions were computed between the actual and variously computed amounts of K to reach sufficiency level based on constant-fraction recovery, quicktest-measured recovery (one-step), and curvilinear regression-adjusted recovery (two-step). The results indicate that the proposed quicktest methodology (2-h K equilibration) combined with a second calibration step based on longer-time K equilibration of representative soils makes possible a greatly improved recommendation for fertilizer K.

¹ Contribution from the Dep. of Agronomy, Ohio State University, Columbus, and Ohio Agric. Res. and Development Center, Wooster. Approved for publication as Journal Art. no. 135-81 OARDC, Wooster, OH 44691.

² Professor and former Research Associates, respectively. Financial support from the International Fertilizer Development Center, Muscle Shoals, Ala., administered by Midwest Universities Consortium for International Activities, Inc., Columbus, Ohio, is gratefully acknowledged.

Received for publication August 10, 1981. Accepted for publication August 2, 1982.

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