Improved Corrective Fertilizer Recommendations Based on a Two-Step Alternative Usage of Soil Tests: II. Recovery of Soil-Equilibrated Potassium1
- E. O. McLean,
- J. L. Adams and
- R. C. Hartwig2
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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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