Scientia Horticulturae 186 (2015) 254–265 Contents lists available at ScienceDirect Scientia Horticulturae journal h om epa ge: www.elsevier.com/locate/scihorti Biofortification of zinc in onions (Allium cepa L.) and soil Zn status by the application of different organic Zn complexes Patricia Almendros ∗ , Ana Obrador, Demetrio Gonzalez, Jose M. Alvarez Department of Chemistry and Agricultural Analysis, College of Agriculture, Technical University of Madrid (UPM), Ciudad Universitaria s.n., 28040 Madrid, Spain a r t i c l e i n f o Article history: Received 8 October 2014 Received in revised form 3 February 2015 Accepted 16 February 2015 Available online 23 March 2015 Keywords: Agronomic Zn biofortification Zn concentration Zn uptake Transfer factor % Utilization a b s t r a c t A pot experiment was conducted to determine the influence of different natural and synthetic organic Zn complexes on the agronomic biofortification of onion (Allium cepa L.) in two types of soil: Soil acid (weakly acidic) and Soil calc (calcareous). Eight different organic Zn complexes were administered at two different Zn application rates. We determined the Zn distribution in different soil fractions and the Zn availability, pH and redox potential in soils with Nil-Zn and Zn treatments. The effectiveness of Zn sources in onion was assessed in terms of total Zn concentration, soluble Zn concentration, plant biomass and chlorophyll and carotenoid contents. Beneficial effects of Zn on onion response (DM plant biomass, total and soluble Zn concentration, utilization of applied Zn, etc.) were observed, with significant increment in the determined plant parameters, in comparison with the Nil-Zn treatment. The rates of increase varied among sources depending on the soil. Applications of Zn-aminolignosulfonate (Zn-AML) at the rate of 10 mg Zn kg -1 in Soil acid and of Zn-DTPA-HEDTA-EDTA at the rate of 10 mg Zn kg -1 in Soil calc produced the highest Zn and soluble Zn concentrations in plants. In general, the highest concentrations of Zn in labile forms and of potentially available Zn concentrations in both soils were associated with the application of the sources that contained Zn chelated by EDTA and/or DTPA. Zinc source and soil characteristics had a great influence on agronomic Zn biofortification in onions and therefore also on the quality and plant biomass of the crop. Applying Zn organic complexes to an onion crop improved not only productivity, but also Zn concentrations in onion. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Onion (Allium cepa L.) is a high-value crop (Sullivan et al., 2001) and the second most important horticultural crop after tomato (Griffiths et al., 2002). It is widely used as a flavoring vegetable in different types of food. This crop is a source of vitamins and is val- ued for its antimicrobial and antioxidant activity, anticarcinogenic Abbreviations: CAR, carbonate bound; DM, dry matter; Eh, redox potential; EXC, exchangeable bound; FAAS, flame atomic absorption spectrophotometry; FeOx, iron oxides bound; FM, fresh matter; Zn-HEDTA, [Zn-N-2-hydroxyethyl- ethylenediaminetriacetate]; LMWOAs, low molecular weight organic acids; MES, [2-(N-morpholino)ethanesulfonic acid]; MnOx, Mn oxides bound; OM, organic matter bound; RES, residual; TEA, triethanolamine; TF, transfer fac- tor; WS, water soluble bound; Zn-DTPA, Zn-diethylenetriaminepantaacetate; Zn-DTPA-HEDTA-EDTA, Zn-diethylenetriaminepentaacetate-N-2-hydroxyethyl- ethylenediaminetriacetate-ethylenediaminetetraacetate; Zn-EDDHSA, Zn-eth ylenediamine-N,N ′ -bis(2-hydroxyphenylacetate); Zn-EDTA, Zn-ethylenediaminet etraacetate. ∗ Corresponding author. Tel.: +34 913365650. E-mail address: p.almendros@upm.es (P. Almendros). and antimutagenic properties and protection against cardiovascu- lar disease (Corzo-Martinez et al., 2007; Stajner and Varga, 2003). Zinc is essential in plant nutrition and is a fundamental compo- nent of various enzyme systems, in which it contributes to energy production, protein synthesis and growth regulation (Mortvedt, 2014; Ngole and Ekosse, 2009). A study conducted by the Food and Agriculture Organization (FAO) showed that Zn deficiency is the most common micronutrient deficiency and affects a wide range of soil types in many different agricultural areas (IZA, 2014). Onion is a species which is particularly sensitive to Zn defi- ciency, with a relatively high responsiveness to Zn (Alloway, 2008; ILZRO, 1975; Mortvedt, 2014; Viets et al., 1954). Various authors have reported that applications of Zn significantly increase onion biomass, plant growth, Zn concentration and bulb quality (Gamelli, 2000; Maurya and Lal, 1975; Phor et al., 1995; Satbir et al., 1989). Zinc deficiency is also a common nutritional problem in humans (Cakmak et al., 1999). Low levels of Zn in food crops are thought to be responsible for human Zn deficiency (Hotz and Brown, 2004). Zinc is an essential micronutrient for various functions in the http://dx.doi.org/10.1016/j.scienta.2015.02.023 0304-4238/© 2015 Elsevier B.V. All rights reserved.