Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1973 Characterization of soil phosphates with chelates: ethylenediaminetetra-acetic acid (EDTA) and nitrilotriacetic acid (NTA) Lambert Akparu Nnadi Iowa State University Follow this and additional works at:https://lib.dr.iastate.edu/rtd Part of theAgricultural Science Commons,Agriculture Commons, and theAgronomy and Crop Sciences Commons Recommended Citation Nnadi, Lambert Akparu, "Characterization of soil phosphates with chelates: ethylenediaminetetra-acetic acid (EDTA) and nitrilotriacetic acid (NTA) " (1973).Retrospective Theses and Dissertations. 5110. https://lib.dr.iastate.edu/rtd/5110 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. 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Silver prints of "photographs" may be ordered at additional charge by writing the Order Department, giving the catalog number, title, author and specific pages you wish reproduced. 5. PLEASE NOTE: Some pages may have indistinct print. Filmed as received. Xerox University Microfilms 300 North Zeeb Road Ann Arbor, Michigan 48106 I I 74-9144 NNADI, Lambert Àkparu, 1939- ŒARACTERIZATION OF SOIL PHOSPHATES WITH ChhiAii:S--mrinjiNEDIAMIfEIEIRÂÂCEriC ACID (EDTA) AND MTRILOTRIACETIC ACID (NTA). Iowa State University, Ph.D., 1973 Agroncsny ; University Microfihns, A aEwKCompany, Ann Arbor, Michigan TUTC nTCC-CTDTATTDM HAQ RPPKT MTrDACTTMPn FYArTT.Y AR PFrFTA^Pn Characterization of soil phosphates with chelates - ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) by Lambert Akparu Nnadi A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of The Requirements for the Degree of DOCTOR OF PHILOSOPHY Department: Agronomy Major: Soil Fertility Approved; Signature was redacted for privacy. Signature was redacted for privacy. Signature was redacted for privacy. Iowa State University Ames, Iowa 1973 ii TABLE OF CONTENTS Page PART 1. INTRODUCTION 1 PART 2. LITERATURE REVIEW 4 PART 3. MATERIALS AND METHODS 40 PART 4. DEVELOPMENT OF METHOD FOR DETERMINATION OF INORGANIC P IN AQUEOUS SOLUTIONS OF EDTA OR NTA 52 PART 5. DEVELOPMENT OF METHOD FOR DETERMINATION OF INORGANIC P IN EDTA OR NTA EXTRACTS OF SOILS 68 PART 6. FACTORS AFFECTING EDTA- AND NTA-EXTRACTABLE INORGANIC P AND ASSOCIATED CATIONS IN SOIL 79 PART 7. RELATIONSHIPS BETWEEN INORGANIC P AND ASSOCIATED CATIONS EXTRACTED BY EDTA OR NTA SOLUTIONS 106 PART 8. SUMMARY AND CONCLUSIONS 151 LITERATURE CITED 157 ACKNOWLEDGMENTS 168 APPENDIX A. AMOUNTS OF P AND METAL IONS EXTRACTED FROM SOME SURFACE SOILS BY EDTA SOLUTIONS OF DIFFERENT pH VALUES AND CONCENTRATIONS 169 APPENDIX B. AMOUNTS OF P AND METAL IONS EXTRACTED FROM SOME SURFACE SOILS BY NTA SOLUTIONS OF DIFFERENT pH VALUES AND CONCENTRATIONS 178 APPENDIX C. AMOUNTS OF P AND METAL IONS EXTRACTED FROM SURFACE AND SUBSOILS WITH 1Û0 inM EDTA ADJUSTED TO pH VALUES OF 4, 6, F, OR 10 187 APPENDIX D. AMOUNTS OF P AND METAL IONS EXTRACTED FROM SURFACE AND SUBSOILS WITH 100 mM NTA ADJUSTED TO pH VALUES OF 4, 6, 8, OR 10 192 APPENDIX E. SIMPLE CORRELATION COEFFICIENTS AMONG P AND METAL IONS IN EDTA OR NTA EXTRACTS OF SOILS 197 1 PART 1. INTRODUCTION The soluble salts of ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) have wide industrial and agricultural applications. NTA is becoming increasingly well known because of its potential use as a partial substitute for polyphosphates in the detergent industry. Because of the comparatively low cost of manufacture and the high chelating power, increasing quantities of NTA have been used for deter­ gent formulations since 1966. EDTA and NTA are now widely employed in agriculture as carriers for micronutrients (Zn, Mn, Fe, Cu, Mo). NTA chelated micronutrients have been mostly granular formulations for zinc and iron; EDTA chelated micronutrients, which have been in use for a longer period of time than NTA, include powdered, granu­ lar, and liquid formulations for iron,- zinc,- copper, and manganese. EDTA is used as a food preservative. Both chelates find extensive use for removal of hardwater scales from industrial plants. NTA has been used for 2,4-D herbicide concentrates which are completely soluble in water. In aqueous solutions, chelating agents such as EDTA and NTA form strong, soluble complexes with polyvalent cations and thereby eliminate the detrimental effects often caused in aqueous systems by metallic impurities. The dyeing, textile 2 processing, tanning, and photographic industries use those chelates for the removal of metal-ion contaminations in their sources of water. But the addition of such compounds to soils or natural waters by detergent products released from sewage treatments could cause adverse effects by binding cations associated with soil or sediment phosphate and releasing the phosphate to the aqueous phase of the soil-water or sediment- water systems. This release of phosphate may lead to eutro- phication of water resources by phosphate derived from soils and sediments. Since NTA complexes iron, aluminum, calcium, magnesium, and other metals, information concerning its effects on the release of phosphate associated with these metal ions in soils or river, and lake sediments, is of vital importance in relation to possible use of this compound as a substitute for phosphates in detergents. On the other hand, the ability of EDTA and NTA to bind Fe, Al, Ca, Mg, and other metal ions makes them potentially useful extractants for the study of phosphates in soils and, possibly, in soil testing for fertilizer recommendations. Also, these compounds could serve as a single extractant for the determination of not only phos­ phates but also other ions of interest in soils, particularly the micronutrient elements. A few attempts have been made to use EDTA to bind the various metal ions in soils and thereby release the phosphate 3 associated with these metal ions. But difficulties have been encountered in the determination of the released phosphate because EDTA interferes with phosphomolybdenum color developed in the colorimetric methods employed for determination of phosphate. Probably because of this difficulty, very few investigations have been conducted to determine the potential use of these chelates in the characterization of soil phos­ phates, although EDTA has been widely employed for the ex­ traction of some micronutrients from soils. To my knowledge NTA has not been used in studies related to phosphates in soils. The objectives of this investigation were: (a) to develop a satisfactory colorimetric method for the determination of phosphates in aqueous solutions and soil ex­ tracts of EDTA and NTA; (b) to study the factors that affect the release of soil phosphates by EDTA and NTA solutions; (c) to investigate any possible relationships between EDTA- and NTA-extractable phosphates and calcium, magnesium, iron, and aluminum ions in the surface and subsoils of the major soil types in Iowa. 4 PART 2. LITERATURE REVIEW Chemistry of Soil Phosphates Since the investigation is related to inorganic phos­ phates in soils, it is essential that some aspects of the chemistry of inorganic phosphates in soils be reviewed. In addition, the literature related to the use or potential use of chelates in studies of soil phosphates will be surveyed. Forms of inorganic phosphates in soil Phosphorus compounds in soils can be classified into two broad categories: "organic and inorganic. The relative amounts of these two categories in a given soil depend on the organic matter content and the age of the soil. The insoluble or slightly soluble forms of inorganic P in soils include the oxy- and hydroxy-phosphates of Fe"*"^, Fe^^, Al^^' Mg*^' Ca^^, +2 +4 Mn , and Ti . Of the above, iron, aluminum, and calcium phosphates will predominate. However, magnesium phosphates may be important in soils derived from dolomite. In acid soils, aluminum and iron phosphates are the domi­ nant fractions. Of the various iron oxides in highly weathered soils, goethite FeCOH)^ is the most stable. Gibbsite, AKOH)^/ is the most stable form of the aluminum compounds. Therefore, these two compounds would be expected to control the solu­ bility of iron and aluminum phosphates in acid soils. Also postulated to be present in acid soils are variscite. « 5 AlPO^-2 HgO, and strengite, FePO^'ZH^O. This postulate is supported by the solubility product calculations of Lindsay and Moreno (1960). But Bache (1963) found that in pure systems only at pH less than 3.1 does the solubility of variscite control the P concentration. At higher pH values he found that variscite dissolved with the formation of aluminum hydroxyphosphate. He stated that strengite was never likely to be in equilibrium with any soil solution, but could be associated with colloids as surface complexes. In alkaline soils the native minerals are largely hydroxy- apatite Ca (PO^) g (OH) 2 » fluor apatite Ca (PO^) gF2, or mixtures ^Q ^^Q of both (Bassett, 1917). Smith and Lear (1966) identified some carbonate apatites and some substituted fluorapatite in which carbonate plus fluorine replaced some phosphates and sodium and magnesium replaced some calcium. Larsen (1967) in a review of soil phosphorus suggested that there was no reason to assume any calcium phosphate other than hydroxy-phosphate is permanent­ ly present in slightly acid, neutral, and alkaline soils. The effect of carbonate on hydroxyapatite was to make it more chemically reactive. The different forms of inorganic P are associated with different mineral fractions of the soil. Most of the in­ organic P occurs in clay fractions. Hanley and Murphy (1970) analyzed the phosphate forms in particle-size separates in twenty-four Irish soils and found all forms of P were highest