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This article in SSSAJ

  1. Vol. 74 No. 5, p. 1642-1651
    Received: May 20, 2009

    * Corresponding author(s): nslaton@uark.edu
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Correlation and Calibration of Soil Potassium Availability with Soybean Yield and Trifoliolate Potassium

  1. Nathan A. Slaton *a,
  2. Bobby R. Goldenb,
  3. Russell E. DeLonga and
  4. Morteza Mozaffaric
  1. a Dep. of Crop, Soil, and Environ. Sciences, Univ. of Arkansas, 1366 W. Altheimer Dr.Fayetteville, AR 72704
    b LSU Agricultural Center, Red River Research Station, 262 Research Station Dr.Bossier City, LA 71112
    c Univ. of Arkansas, Marianna Soil Test Lab, Hwy. 1 South, P.O. Drawer 767, Marianna, AR 72360


The ability of soil tests to identify nutrient-deficient soils and recommend fertilizer rates that optimize agronomic yield is essential for profitable soybean [Glycine max (L.) Merr.] production. Our objectives were to correlate relative soybean yield to Mehlich-3 and 1 mol L−1 HNO3–extractable soil K and trifoliolate-leaf K concentration at the R1 to R2 development stage and calibrate the K rates for Mehlich-3-extractable soil K. Experiments were established on silt loams at 34 site-years planted with a Maturity Group IV or V cultivar and fertilized at five K rates (0–148 kg K ha−1). Mehlich-3-extractable soil K ranged from 46 to 167 mg K kg−1 and produced relative soybean yields of 59 to 100% when no K was applied. Eleven sites had Mehlich-3-extractable K < 91 mg K kg−1 and all responded positively to K fertilization. Soybean grown in soil having 91 to 130 mg K kg−1 responded positively at nine of 15 sites. Mehlich-3 soil K explained 76 to 79% of the variability in relative yields and had critical concentrations of 108 to 114 mg K kg−1, depending on the model. The linear-plateau model predicted the critical HNO3–extractable soil K to be 480 mg K kg−1 Trifoliolate-leaf K concentration increased significantly, positively, and linearly as Mehlich-3- and HNO3–extractable soil K increased, but Mehlich-3 soil K explained only 49 to 53% of the variation in trifoliolate-leaf K. Mehlich-3-extractable K is an excellent predictor of soil K availability for soybean grown on silt loams in eastern Arkansas.

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