Studies on the Extraction and Availability of Micronutrients in Soil

Malik, Allah Bakhsh (1993) Studies on the Extraction and Availability of Micronutrients in Soil. PhD thesis, University of Glasgow.

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Chapter one includes the survey of dynamic equilbria and the forms of micronutrients which exists in fractions. The sources of micronutrients as influenced by natural conditions and anthropogenic metal addition are also discussed. The presence of micronutrient cation in different pools and the removal of metals from these pools in soil are reviewed. Extractable levels of micronutrients in soil are affected by various factors. The forms of trace metals as influenced by these factors are also discussed. The objectives of the thesis are to study the removal of micronutrient in soil from different pools and also the changes in the distribution of these metals with plant uptake. Chapter 2 is comprised of the physical properties of the soil study and the slective extraction procedures for the measurement of soil Co, Cu, Fe, Mn, Ni and Zn. Chapter 3 consisted of the removal of exchangeable metal by using simple metal salts. The removal of micronutrients associated with exchangeable fraction in the soil is affected by the nature of the extracting solution, extractant concentration and by the replacing cation. Extraction of exchangeable metals with different salts of acetate, nitrates and chlorides showed non detectable level of Co, Cu and Ni from all the soils. Which indicated that large proportion of these elements are associated with organic and oxide bounds fractions. Nitrates and chlorides appeared to extract large quantity of Mn and Zn and very small amount of Fe. While, ammonium acetate extracted more Fe than Mn and Zn from these soils. It indicates that kind of the cation also plays an important role on the exchange of micronutrients. Amount of Fe, Mn and Zn extracted by various salts of acetate, nitrates and chlorides for most of the soils were increased with the increase of extractant concentrations. Which suggested that higher concentrations of different salts extract a fraction of trace metals from these soils, which was retained by the soil when extracted with lower concentrations of the extracts. Chapter 4 lays emphasis on the removal of metals associated with organic matter and oxide bound fractions. Comparison between the pairs of extractants and individual extractant are studied for the removal of Cu, Fe, Mn and Zn. It is found that there is no big difference betwen the two pairs of extractants. Ammonium EDTA (0.05M) pH 7.0 is suggested a common extractant for the removal of organic matter fraction of Cu, Fe, Mn and Zn in preference to pyrophasphate and sodium hydroxide. As pyrophosphate also affected the oxide pool and NaOH extracted very small amount of Mn and Zn from all the soils. Acid oxalate is suggested for the dissolution of oxide bound fraction, as it extractes more Cu, Fe, Mn and Zn than the hydroxylamine hydrochloride from all the soils. Whereas NH2OH.HCl extractable copper was below the detection limit. In soil extracts metals are present in suspended materials. In this study, soil extracts were cleared by precipitation of suspended materials and organic matter with filtration through 0.45?m filters. It is observed that extractable amount of Cu, Fe, Mn and Zn are decreased after filtration through 0.45?m filters and ultrafiltration of the soil extracts are suggested for further study of these elements. Chapter 5 investigates the influence of continuous cropping of ryegrass on the distribution of Cu, Fe, Mn and Zn in soil using a pot experiment and assessess this by means of specific extractants. Calcium chloride, acetic acid, ammonium EDTA and acid oxalate were used to extract Cu, Fe, Mn and Zn associated with exchangeable, specific adsorbed, organic matter and oxide bound fractions, respectively. It was found that CaCl2 and acetic acid extractable Cu and Fe were very small or below the detection limit, and large quantity of Mn and Zn were present in these pools. Which indicates that Mn and Zn are more easily available to plants than that of Cu and Fe. As the large quantity of Cu and Fe were present in organic matter and oxide fractions, which indicates that organic and oxide fractions are the big reservoir of Cu and Fe. It is also observed that extractable amount of Cu and Zn decreased in the first 10 weeks and than remain unchanged, whereas the amount of Fe and Mn showed a small increased from initial to ist 10 week of samplings and thereafter it remain unchanged. The amount of Cu and Zn taken up by grass are higher in soils with the higher levels of Cu and Zn. The uptake of Mn was higher in soil with high Mn in readily available pools and the uptake of Fe was higher in the soil of lower Fe content, rather than the higher total amounts, suggesting that total Fe and Mn is not a good indicator for plant uptake.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: I D Pulford
Keywords: Soil sciences, Biogeochemistry
Date of Award: 1993
Depositing User: Enlighten Team
Unique ID: glathesis:1993-74641
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 27 Sep 2019 17:24
Last Modified: 27 Sep 2019 17:24

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