Optimization of solutionrsoil ratio and shaking times of the mehlich-in soil test on histosols

S. Rezaian, E. A. Hanlon, C. A. Sanchez, J. A. Cornell

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


The University of Florida Everglades Soil Testing Laboratory has been determining water-extractable P in organic soils (Histosols) since 1944. the water extractant has consistently provided reliable correlations for vegetable commodities, but not for agronomic crops. Recent research has suggested that the Mehlich-III soil test has potential for use on Histosols. However, no information indicated if solutionrsoil ratios (RAs) and shaking times (SHs) used for mineral soils would be appropriate for organic soils, which have appreciably lower soil bulk densities. A laboratory study with SHs ranging from 1 to 29 min and RAs ranging from 8 to 22 (v/v) arranged in a central composite rotatable design (ccd) was conducted using four Florida Histosols. Nine treatment combinations of RAs and SHs were used. Two replications of the ccd were performed with duplicate extractions for each sample. the fitted second-degree response surface equations for P and K nutrients with surface contour plots were shown for each of the four soils. the intent was to discern if RAs and SHs would impact P and K so that these nutrients could be extracted from the soil in a short time with little chemical waste. Across the four soils, the amounts of extracted P and K in this study were increased at high levels of RAs and SHs. It is disadvantageous to seek out high values of extracted nutrients at the cost of extra time, increased chemicals, and increased manpower demand per day. the maximum (0.8-3 fold) increase in extracted P and K that could be obtained at high levels of RAs and SHs is not important from an analytical viewpoint and would not justify the increase in cost and time. Extracted P and K levels for all soils were well above the lower limits for standard analytical procedures. Within each soil, the models for P data predicted a higher coefficient of determination (R2) than did the models for K. Since no optimum RA and SH combinations were found, the published values- standard RA = 10:1 (v/v) and SH = 5 min-appear to be acceptable for Florida Histosols to minimize laboratory analytical time and chemical waste or costs.

Original languageEnglish (US)
Pages (from-to)2247-2259
Number of pages13
JournalCommunications in Soil Science and Plant Analysis
Issue number17-20
StatePublished - Nov 1 1992
Externally publishedYes

ASJC Scopus subject areas

  • Agronomy and Crop Science
  • Soil Science


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