Effect of Application Methods and Different Sources of Fe Fertilizer on the Growth and Physiological Characteristics of Tomato in Hydroponic System

Iron is an essential element for plant growth which is involved in many plant processes such as photosynthesis and activating enzymes involved in mitochondrial and photosynthetic electron transfer. Iron (Fe) deficiency is a common disorder affecting plants in many areas of the world, and is chiefly associated with high pH, calcareous soils. Plant Fe deficiency has economic significance, because crop quality and yields can be severely compromised. Deficiency or low activity of iron in the plant causes chlorophyll is not produced in sufficient quantities and the leaves are pale. The decrease of chlorophyll leading to the reduction of the plant food processor and finally the yield is reduced. Iron fertilizers are grouped into three main classes: inorganic Fe compounds (soluble ones such as FeSO4·7HO), synthetic Fe chelates [such as ethylenediamine tetraacetic acid (EDTA) and ethylenediamine-di (o-hydroxyphenylacetic acid) (EDDHA)] and natural Fe-complexes (humates and amino acids). Iron could be applied in different chemical forms, including chelates and inorganic Fe salts. To our knowledge, no published data for tomato growing under hydroponic conditions have assessed the effects of application methods and different sources of Fe Fertilizer on plant yields, growth and nutritional condition. Therefore, this work was carried out to study the effect of FeSO4, Fe-EDTA, Fe-EDDHA and Fe-DTPA as a foliar spray and root-applied on the growth, yield, physiological characteristics of tomato plants under hydroponic system.

Regarding to the role of application methods and Fe sources on the absorption of this element and the process of photosynthesis and plant growth, a factorial experiment was carried out to determine the best methods of application (add to nutrient solution and foliar spray) and iron fertilizer (FeSO4, Fe-EDTA, Fe-DTPA and Fe-EDDHA) for growth and physiological characteristics of tomato in hydroponic system with three replications. Analysis of variance (ANOVA) was performed using the SAS program. If ANOVA determined that the effects of the treatments were significant (P ≤0.01 for F-test), then the treatment means were separated by Tukey range test.

The results indicated that the plant height, dry and fresh weight affected by the application methods and iron fertilizer, so that the maximum and minimum plant height, and dry and fresh weight were obtained in application of Fe-EDTA to nutrient solution and foliar application of FeSO4, respectively. Mohammadipour et al., (2013) reported that by applying nano-chelate fertilizer of iron, iron sulfate, Fe-EDTA and Fe-EDDHA by two methods of foliar application and root-applied (soil) of Spathiphyllum plant, a significant difference between the types of fertilizer and application method were used. So that the maximum height and dry weight of the plant were obtained in Fe-EDDHA fertilizer treatment to the root application. The root and leaf Fe concentration affected by source of iron and the method of application so Fe-EDTA added to nutrient solution and foliar application had the highest amount of Fe in the root and leaf, respectively. Cu, Mn, Zn and some macro elements such as; Mg and P also influenced by the type of fertilizer and method of application. Roosta and hamidpour (2013) showed that the foliar application of Fe-EDDHA under aquaponic and hydroponic conditions increased the amount of K, Mg, Fe and decreased the concentration of Zn, Cu and Mn compared to the control treatment in tomato plants. Current experiment results showed that the maximum chlorophyll content (a, b and total) and maximal quantum yield of PS II photochemistry (Fv/Fm) and performance index (Pi) values of young and old leaves were found with Fe-EDTA in nutrition solution and the highest carotenoids and sugar soluble content were found in FeSO4 in nutrient solution and foliar application, respectively. Roosta and Mohsenian (2012) reported that there was also a linear relationship between leaf-Fe and chlorophyll content in pepper. The application of inorganic Fe salt (FeSO4) and Fe-chelates (Fe-EDDHA and Fe-EDTA) on pepper plants increased Chl a content in leaves of these plants compared to the control. Additionally, several investigations have described the beneficial effects of foliar Fe. Iron deficiency caused a significant reduction in the amount of chlorophyll a, b, total and carotenoids of pea (Iturbe-Ormaetxe et l., 1995).

Based on the results, Fe-EDTA and Fe-EDDHA had the highest significant effect on vegetative growth of tomato, respectively. Thus, at neutral pH of nutrient solution as occurred in this experiment, application of Fe-EDTA in nutrition solution is suitable than the other source of iron fertilizer for tomato growth.