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Fluid Journal : Winter 2012
5 The Fluid Journal Winter 2012 Foliar application. In Central Anatolia, where Zn deficiency is a well- documented problem in Turkey, soil application of Zn fertilizers significantly increased both grain yield and grain concentrations of Zn (Figure 2). However, combined application of soil and foliar Zn fertilizers is more effective in enhancing grain Zn concentration, and causes increases in grain Zn concentration up to three-fold. The effect of soil-applied Zn fertilizer on grain Zn concentration is not sufficiently high in soils with an adequate amount of plant available Zn. Under such conditions, foliar application of Zn fertilizers is an essential practice in order to improve grain Zn concentration of cereal crops at adequate amounts for better human nutrition. Recent studies report 0.5 to 1.0 kg Zn ha-1 as the most commonly used rates of Zn in foliar applications to correct Zn deficiency in plants. Foliar application of Zn fertilizers can be performed by using either ZnSO4 or chelated forms of Zn (e.g., Zn-EDTA). Our recent results show that ZnSO4 is a better Zn source in increasing grain Zn concentration when compared to ZnEDTA and ZnO when foliar sprayed on wheat. Timing of Zn spray on foliage plays an important role in the effectiveness of the foliar-applied Zn fertilizers in increasing grain Zn concentration. Particular increases in Zn deposition into grain can be achieved when foliar Zn fertilizers are applied to plants at a late growth stage. Past studies have monitored changes in Zn concentration in wheat grain during grain development and found that the highest accumulation of Zn in grain takes place during the milk stage of grain development. It has been shown that foliar spray of Zn late in the growing season in wheat (e.g., at milk and dough stage) resulted in much larger enhancement in grain Zn concentration when compared to the application of Zn at earlier growth stages (Table 2). Increases in concentration of whole grain Zn associated with late foliar Zn applications were also well reflected in various fractions such as embryo, aleurone, and endosperm. The increases found in the concentration of endosperm Zn through Zn spray during the reproductive growth stage were particularly impressive (Figure Figure 1. Effect of intercropping peanut with maize plants on Fe concentration of shoot, roots, and seeds of peanut plants grown on a calcareous soil (Zuo and Zhang, 2009). Figure 2. Grain Zn concentrations of durum wheat treated by foliar application of ZnSO4 (A) and increasing amount of Zn fertilization into soil (B) grown on a highly Zn-deficient calcareous soil under field conditions in Central Anatolia (Cakmak et al., 2010a) 3). These increases in endosperm Zn concentration may have important impacts on human nutrition because the endosperm part is the most commonly eaten part of wheat in a number of countries where Zn deficiency incidence in human population is very high. Nutritional status. Nitrogen nutritional status of plants has also positive impacts on grain concentration of Zn. Increase in grain Zn concentration by applying soil and/ or foliar Zn fertilizers is maximized when the N nutritional status of plants is improved either by soil or foliar application of N fertilizers (e.g., urea). It seems that N and Zn act synergistically in improving grain Zn concentration in wheat when Zn and N are sufficiently high in growth media or plant tissues. Most probably, improving N nutritional status of plants contributes to better root Zn uptake and/or Zn accumulation in grain by affecting at least one of the following processes: 1. root exudation of compounds contributing to solubility and uptake of Zn (e.g., phytosiderophores) 2. root growth and morphology 3. abundance and expression of transporter proteins mediating uptake and transport of Zn in root cells 4. nitrogenous compounds "High zinc concentrations ensure good root growth"
Early Spring 2012