Iron Chelates Supplied Foliarly Improve the Iron Translocation Rate in Tempranillo Grapevine

Iron (Fe) chlorosis is a widespread nutritional disorder in grapevine, particularly in vineyards developed on calcareous soils. Despite the effective application of highly efficient Fe chelates such as Fe¿ethylenediamine di-o-hydroxyphenylacetic acid (EDDHA) to the soil to solve the problem, the cost of the treatments and the loss of effectiveness of the chelate in the soil in rainfed crops limit their use. An alternative could be the utilization of Fe fertilizers directly supplied through foliar spray. Two Fe chelates [Fe¿ethylenediaminetetraacetate (EDTA) and Fe¿ethylenediamine disuccinic acid (EDDS)], an Fe complex (Fe-lignosulfonate), and an Fe salt (Fe-sulfate) were foliarly applied to mature Tempranillo tinto (Vitis vinifera L.), grown on a soil with a high active lime (most reactive calcium carbonate phase in soils) content (92.5 g kg¿1 at 30¿60 cm deep), and compared to an untreated control. Three shoots per vine and five vines per treatment were selected. One hundred mL of each Fe treatment (5 mM) were sprayed on mature leaves (treated), and young leaves (covered) were covered so Fe translocation could be studied. Treatments were repeated once after 2 weeks. Leaf blades were sampled before the first spray application and at the end of the assay, 4 weeks later, and 2 weeks after the second spray application. Micronutrient content [(Fe, manganese (Mn), copper (Cu), and zinc (Zn)] in leaf blades was determined and Fe/Mn ratio was calculated as a Fe nutrition index. Leaf chlorophyll content was measured weekly using a noninvasive Minolta SPAD chlorophyll meter. As expected, all Fe treatments resulted in greater leaf Fe concentration than in the untreated control; however, leaves sprayed with Fe-EDTA and Fe-sulfate showed the greatest Fe concentration. As consequence, the largest Fe/Mn ratio was found for Fe-EDTA and Fe-sulfate treatments, although no differences with Fe-EDDS treatment were found. Leaves sprayed with Fe-EDTA chelate showed not only the greatest SPAD readings at the end of the field experiment but also the greatest SPAD readings when measured on covered leaves from the 15th day after treatment application when compared to untreated control. Covered leaves from all vines sprayed with Fe treatments showed greater Fe concentrations than untreated control but only the Fe/Mn ratio for Fe-EDTA was significantly greater than that of untreated control. The inconsistency between total Fe concentration from the sprayed leaves and SPAD readings in both sprayed and covered leaves suggests that the proposed methodology is valid for assessing the Fe translocation rate from mature to young leaves when foliar fertilization was appliedFinancial support was provided by the AGL2010-18048 Project, funded by the Ministerio de Ciencia e Innovación (Spain).Peer Reviewe