Behavior of Zinc from Six Organic Fertilizers Applied to a Navy Bean Crop Grown in a Calcareous Soil D. GONZALEZ, A. OBRADOR, AND J. M. ALVAREZ* Department of Chemistry and Agricultural Analysis, College of Agriculture, Polytechnic University of Madrid (UPM), Ciudad Universitaria s/n, 28040 Madrid, Spain The objective of this study was to compare the mobility, leaching, availability, and relative effectiveness of Zn from Zn-polyhydroxyphenylcarboxilate (Zn-PHP), Zn-HEDTA (Zn-N-2-hydroxyethyl-ethyl- enediaminetriacetate), Zn-EDDHSA [Zn-ethylenediamine-di-(2-hydroxy-5-sulfophenylacetate)], Zn- EDTA (Zn-ethylenediaminetetraacetate), Zn-S,S-EDDS (Zn-ethylenediaminedisuccinate), and Zn- EDTA-HEDTA sources by applying different Zn rates (5 and 10 mg kg -1 ) to a calcareous soil under greenhouse conditions. A lysimeter experiment was carried out for 60 days and using navy bean (Phaseolus vulgaris L.) as an indicator plant. The Zn available to the plant and easily leachable Zn were determined in soil by different single extractions, while the distribution of Zn in the soil was assessed by sequential speciation. The utilization of applied Zn by the navy bean was greatest when the Zn treatments were Zn-EDTA, Zn-EDTA-HEDTA, Zn-HEDTA, and Zn-EDDHSA. Both total Zn in the plants and soluble Zn in the plant dry matter (extracted with 1 mM 2-morpholino- ethanesulfonic acid) were positive and significantly correlated with the following: the amounts of Zn extracted with the three single extractions used to estimate soil available Zn and the amounts of Zn in the water soluble plus exchangeable and organically complexed fractions. The Zn-HEDTA, Zn- EDDHSA, Zn-EDTA-HEDTA, Zn-S,S-EDDS, and Zn-EDTA sources significantly increased the mobility of micronutrients through the soil with respect to the control and Zn-PHP source. The maximum Zn concentration obtained in the leachate fractions was 65 mg L -1 (13% of Zn applied) for the Zn-S,S-EDDS chelate applied at a rate of 10 mg Zn kg -1 soil. In the course of the crop, the soil pH + pe parameter increased significantly with experimental time. KEYWORDS: Availability; chelates; plant response; sequential speciation; micronutrient INTRODUCTION Zinc deficiency is a critical nutritional problem in plants and is responsible for low yield and poor plant quality in some parts of the world (1-3). Plants are known to differ in their susceptibility to particular mineral deficiencies (4), e.g., navy bean (Phaseolus Vulgaris L.) cultivars are generally susceptible to soil Zn deficiency, which is at least partly due to the poor translocation of Zn from the roots to the tops of plants (5, 6). In contrast, high concentrations of Zn can be toxic for plants and animals and constitute a potential contaminant in soils (7-9). Certain soil conditions like high pH (e.g., in calcareous soil), poor aeration, low organic matter content, high clay content, and/or P supply, are known to promote Zn deficiency (3, 10). Such soils therefore need Zn supplements. Inorganic fertilizers (mainly Zn sulfate) have been traditionally used for this purpose, but other organic Zn sources (synthetic chelates and natural complexes) are also commonly used (11, 12). The crop response to Zn fertilization varies according to the Zn fertilizer source (13, 14). The greater mobility of chelated Zn is of agronomic significance in that it suggests that these Zn sources are more likely to move into the root zone and provide feeding sites for the crop. Some studies have reported that applications of chelated forms of Zn to calcareous soils are the most effective for certain crops (15, 16), but column leaching studies have also shown that the addition of some Zn chelates may greatly increase Zn mobility throughout the whole soil column and that important amounts of applied Zn may be lost via leaching (17). For example, when fertilizers contain the ethylenediami- netetraacetate (EDTA) chelating agent, the application of micronutrients to the soil supposes a risk to the environment and especially to groundwaters. This deserves consideration in the development of best management practices to reduce the transport of metals from land to water (9). Micronutrient availability to plants can be measured in direct uptake experiments or estimated using a chemical extractant to remove a fraction of the soil micronutrient pool and relate this fraction to plant response (18). Chemical sequential extraction techniques are commonly used to fractionate the solid-phase forms of metals found in soils (19). These schemes have been applied in environmental solid samples to metal partitioning into * Corresponding author. Fax: 34-91-33-65-639. E-mail: josemanuel.alvarez@upm.es. 7084 J. Agric. Food Chem. 2007, 55, 7084-7092 10.1021/jf071090v CCC: $37.00 © 2007 American Chemical Society Published on Web 07/31/2007