Extractable soils 848 INDEX

Ohno (2002a) investigated concentration and inner filter effects on the humification index. Field com residue extract, water-extractable soil organic matter, and soil fulvic acid... 

Fig. 6. Relationship between the log Koc for phenanthrene sorption and the polarity index of humic acids and humin, sequentially extracted from a soil. F-l, F-4, F-7, and F-9 are the first, fourth, seventh, and nineth extracted humic acids, respectively. 0.005, 0.05, and 0.5 ig mL 1 are selected liquid-phase equilbrium concentration of phenathrene (Kang and Xing 2005).

The second reason for acid-digestion is the determination of the total soil elemental content of, e.g. potassium, phosphorus or trace elements. This is seldom done for potassium in normal soil samples, mainly because the total K in soils is of no value as an index to the availability of K to plants, nor is it always of value in tracing the movement or accumulation of applied fertilizer K (Pratt, 1965). The unreactive soil phosphorus is obtained by subtracting the naturally leached reactive phosphorus from the total phosphorus, and a method for determining the latter by extraction with sulphuric acid and potassium persulphate is cited by Turner and FHaygarth (2000). They analysed... 

There are many different types of soil, and extractant formulations have been fine-tuned to suit the soil. The particular extractant may also be chosen on the basis of familiarity over the years, and because it is easier to compare results with those previously obtained, and hence make recommendations to correct deficiencies based on experience. Usually one is not interested in the total amount of a soil nutrient, rather in the amount that is in a form available to the roots of the plant. Regional advisory laboratories over a long period may have developed index tables relating to the found concentration of nutrient in local soil types and the corrective amount of fertilizer required. It would probably be wise to adopt the same methods that have been used to... 

Organic P is not routinely measured by any extraction procedure, and the conventional P index system cannot be simply applied in organic systems because of the complex interacting dynamics of the organic and mineral P pools in the soil. 

Available K measured by ammonium nitrate gave a good indication of plant available K in the soil for organic systems, but not all extractable K is truly available. The K index system can be used as a reasonable guide for organic systems. 

A number of indexes based on the distribution of organic C in humic and nonhumic fractions are used for the evaluation of the humification level in organic amendments and amended soils (Senesi, 1989). Among others these include the degree of humification (DH), which is calculated as DH% = 100 x (HAC + FAC)/ TEC the humification rate (HR), which is calculated as HR% = 100 x (HAC + FAC)/ TOC and the humification index (HI), which is calculated as HI = NHC/ (HAC + FAC) (Sequi et al., 1986 Ciavatta et al., 1988). TOC represents the total organic carbon in the sample TEC represents the total extractable C by an alkaline solution (NaOH and/or Na4P207) HAC and FAC represent the C content in HA and FA fractions, respectively and NHC represents the nonhumified C content calculated by difference, that is, NHC = TEC - (HAC + FAC). 

SOM, soil organic matter HS, humic substances DH, degree of humification HAC, humic acid C FAC, fulvic acid C TEC, total extractable C HR, humification rate HI, humification index NHC, nonhumified C TOC, total organic C HA, humic acid FA, fulvic acids UV-Vis, ultraviolet-visible FT-IR, Fourier transform infrared NMR, nuclear magnetic resonance ESR, electron spin resonance EEM, excitation-emission matrix. 

Figure 16.38. Correlation between humification index, obtained by fluorescence (A465), as proposed by Milori et al. (2002), and the concentration of SFR, determined by EPR, found in HA extracted from soils of the Brazilian savanna region (Cerrado).

Since at pH 2 virtually all the 4-amino-3,5,6-trichloropicolinic acid will be in the free acid form, this partition coefficient—and therefore the sorption index—would be constant if extraction is the mechanism by which the free acid is absorbed. Table IV shows reasonable constancy for the sorption index over a wide range of organic contents except for the first three soils—i.e., soils 3, 4, and 7. There are at least two possible causes for failure of this relationship in these cases other components contributing significantly to sorption, and analytical uncertainty in or-... 

Hot water extraction of soil boron (B) (Berger Truog 1939) has been used widely to obtain an index of soil B status. The method presents difficulties for routine analysis as it is often difficult to prepare water extracts free of colloidal material. Dilute salt solutions have largely overcome this limitation, two examples being the use of 0.01 M CaCl2-0.05 M mannitol (Cartwright etal. 1983) and hot 0.01 M CaCl2 (Aitken etal. 1987). The empirical method described is based on the use of hot water reflux for soil extraction, with alternative analytical finishes based on a colour reaction and ICPAES. 

Hydrolysis would yield a low estimate of the CEC. The index cation is then extracted from the soil with still another salt solution and measured to give the CEC. 

The salt used to furnish the index cation should be relatively soluble in the alcohol used for sample washing. The low solubility of NaCl in ethanol has been a frequently overlooked source of error. The salt then dissolves during the subsequent extraction step and yields an anomalously high CEC value. Soils containing large quantities of hydroxyoxide or amorphous minerals may also retain salts in particle micropores, so that washing does not completely remove the salts. This also yields high CEC values. 

In a comprehensive report on worldwide studies of micronutrients and the nutrient status of soils, prepared for the Food and Agriculture Organization (FAO) (Rome, Italy) and the Institute of Soil Science (Finland), Sillanpaa (1982) described the status of AAO-extractable Mo determinations. On a worldwide basis, determinations of AAO-extractable Mo have not been found to give a sufficiently reliable index of Mo availability to plants. 

Key Word Index allelochemical activity, bioassay, continuous cropping, epicotyl, extraction, inhibitory, lettuce, life cycle, mass spectrometry, mono and bi-desmoside saponins, mungbeans, purification, radicle, soyasaponins, soil, stimulation, thin layer chromatography, Vigna radiatu L., Lactuca sativa L. 

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