Mehlich 1 extractant

Procedure. Carry out the extraction and then determine phosphorus as in Method 5.9a, except that working standard solutions should be made up in the Mehlich 1 extractant. Determine potassium and magnesium as in Method 5.10, except that standards are made up in Mehlich 1 extractant. Determine calcium as in Method 5.2, except that standards are made up in Mehlich 1 extractant. The composition of composts is so variable that appropriate dilutions of extracts may be required, and calculations adjusted accordingly. 

Mehlich-extractable P decline to barely detectable levels below 50 cm depth. Phosphorus is most likely a limiting nutrient for plant growth in those ecosystems. 

Reed, S.T., M.G. Allen, D.C. Martens, and J.R. McKenna. 1993. Copper fractions extracted by Mehlich-3 from soils amended with either CuS04 or copper rich pig manure. Comm. Soil Sci. Plant Anal. 24 827-839. 

Two typical acid extractants are the Bray (which has two forms, both of which are acidic) and the Mehlich-3. The Bray extractant is a dilute solution of hydrochloric acid and ammonium fluoride [11], The Mehlich-3 extractant is a dilute solution of acetic and nitric acids and also contains ammonium nitrate and EDTA [11], Both are designed to extract soluble, exchangeable, and easily dissolved nutrients, particularly phosphate. While the Bray extractant is designed to extract plant available phosphorus, the Mehlich-3 extractant also extracts potassium [10-12],... 

Mehlich A. Mehlich 3 soil test extractant—a modification of Mehlich 2 extractant. Com. Soil Sci. Plant Anal. 1984 15 1409-1416. 

Mehlich, A. (1984) Mehlich 3 soil test extractant a modification of the Mehlich 2 extractant. Commununications in Soil Science and Plant Analysis 15(12), 1409-1416. 

Site Total P (kgPha-i) NaOH Extractable Mehlich 3 (kgPha-i)... 

Fig. 7.1 Total nutrient stocks and in plant biomass plus soil in rain forest, newly planted Pinus caribaea (6 months old), P. caribaea, and Gmelina arborea plantations at the end of the first rotation (9.5 and 8.5 years old, respectively), and second rotation P. caribaea (1.5 years old) at Jari (Sanchez et al. 1985). H = harvest loss from trees taken when clearing the rain forest for the plantations L = leaching. Total nutrient stock is defined as the sum of all the nutrients in plant biomass (aboveground, litter, detritus, roots) plus total N, available P (extracted by the Mehlich method), and exchangeable K, Ca, and Mg in the top meter of the soil.

Mehlich, A.. 1978. New extractant for soil test evaluation of phosphorus, potassium, magnesium, calcium, sodium, manganese and zinc. Communications in Soil and Plant Analysis 9 455 76. 

Common endpoints of such titrations are pH 7 or pH 8.2, although soils in the field are rarely limed above pH 6 or 6.5. The value 8.2 was chosen historically because it approximates the pH of soil containing free CaCC>3 in equilibrium with the normal CO2 content (0.0003 mol fraction) of the atmosphere. This pH also corresponds closely with the pH of complete neutralization of soil hydroxy aluminium compounds. The pH 8.2 is conveniently maintained by Mehlich s BaCl2-triethanolamine extraction technique. 

Cecchi et al. (2004), however, classihed EDTA, ethyl acetate, methanol, or Mehlich III solutions as harsh extractants that appear to be helpful in determining irreversible sorption of phenolic acids but not bioavailable phenohc acids. I would strongly disagree particularly in regard to neutral EDTA extractions. Our data clearly indicate that this is not the case (see justification above). As a matter of fact it is known that roots and microbes in soil produce a number of chelahng agents that function in a similar manner to EDTA (Nagarajah et al. 1970 Doetsch and Cook 1973 Kaminsky and Muller 1977 Marschner and ROmheld 1996 Fisher 2002 Fisher and Bipp 2002). 

Dalton et al. (1989b) utilizing Mehlich 111, a mild chelating extractant, also observed that the recovery of available phenolic acids (femlic acid, vanillic acid, p-coumaric acid, p-hydroxybenzoic acid) from sterile soil (Cecil, Portsmouth and White Store) varied with soil type, horizon, time, and the type of phenolic acid added. When they allowed phenolic acids added to soil to equilibrate for 2 min before extraction, they noted a significant reduction in recovery of phenolic acids. Recovery declined with time up to 32 days. The decline was most rapid over the first 2 days. The presence of methoxy groups and acrylic side chains increased... 

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