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Indian Journal of Agronomy
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How the application of zinc sulfate chelate may affect phosphorous uptake by rice (Oryza
sativa L.) plant
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H. Hossein Zadeh1, M. Mablaghi2, S. Mashayekhi1, N. Divsalar2, A.P. Salehi2, M.
Miransari3*
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1: Islamic Azad University, Science and Research Branch, Department of Agronomy, Tehran,
Iran
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2: Islamic Azad University, Chalus Branch, Iran
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3*: Corresponding author, Prof. Dr. Mohammad Miransari: 1) Mehrabad Rudehen, Imam Ali
Blvd., Mahtab Alley, #55, Postal number: 3978147395, Tehran, Iran, E-mail:
[email protected], 2) AbtinBerkeh Limited Co., Imam Blvd., Shariati Blvd. # 107, Postal
number: 3973173831, Rudehen, Tehran, Iran, Telfax: (98)2176506628, Mobile:
(98)9199219047, E-mail: [email protected]
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Abstract
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For rice plants to obtain high yields, optimum amounts of nutrients must be supplied at different
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growth stages. However, there are usually positive or negative interactions between nutrients
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such as zinc (Zn) and phosphorus (P). Using Zn sulfate chelate, a completely randomized block
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design experiment with four replicates was performed in 2010 at Tonekabon Rice Research
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Station, Iran, to test the uptake of Zn and P by rice (Oriza sativa L.). Ninety kilograms of
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phosphate fertilization was applied to the soil before seeding. Zinc chelate sulfate was applied to
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the soil before seeding and foliarly (control, 2, 4, 6 and 8 mg/l), one month after transplanting,
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after full flowering, and at the milky stage. The highest and lowest amounts of P in the soil and
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rice straw and grain were related to the control and 8 mg/L treatments, respectively indicating
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that there were significantly adverse interactions between the two nutrients.
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Key words: Antagonistic effects, chelate of zinc sulfate, phosphorus, rice (Oriza sativa L.),
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growth stages
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Introduction
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It is important to use the optimum amount of fertilization for crop production, because otherwise
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it would have unfavorable economical and environmental consequences. Although chemical
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fertilization has been successfully used for rice production during the past three decades, its
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unbalanced use has adversely affected the environment including the soil (Sedri and Malakouti,
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1999). The increased concentration of nitrate in the ground water and cadmium in the paddy
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fields and rice grains are among such adverse effects (Miransari and Mackenzie, 2010).
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Zinc (Zn) is among the most important micro-nutrients necessary for different plant functioning
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including the production of proteins and nucleic acids. Zn translocation is complicated in the
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plant and it is very limited in the phloem (Liu et al., 2003). Zn is also necessary for plant
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metabolism including plant enzymatic activities, production of carbohydrates, proteins, auxin
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and reproduction processes. For example, Zn is necessary for the production of 60 plant enzymes
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and among its important functions its role in the structure of tryptophan as the prerequisite for
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the production of auxin is also of significance (Simmons et al., 2003).
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The important point about nutrient uptake by a plant is their availability to the plant. The
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importance of soil factors such as pH, salinity, structure, moisture, biological activities, etc. play
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a significant role on the availability of nutrients. For example, in calcareous soil, the solubility
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and hence availability of micro-nutrients including Zn decrease significantly. Zinc deficiency is
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very common in paddy soils with acidic pH as well as in the soils with acidic pH and high P
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concentration (Norman et al., 2003). The effects of soil pH on root and microbial activities can
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also influence the availability of soil nutrients. Accordingly, the use of foliar application,
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especially for micronutrients, has become common as it increases the utilization efficiency of
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micronutrients by plant (Marschner, 1995; Miransari, 2012).
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Phosphorus (P) is also an essential element for different plant functions. The most important
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function of P in plant is the storage and transfer of energy as well as the membrane stability at
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different growth stages. The critical level of P in the soil using the Olsen’s method is 5 mg/kg in
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acidic soils, which is also subjected to immediate fixation by soil particles (Marschner, 1995).
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According to Marschner (1995) parameters such as Zn content, dilution effect, as well as P
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availability in the soil affect Zn uptake by plants. Under tropical conditions, due to P fertilization
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and use of lime, Zn deficiency is intensified. There are some other parameters affecting Zn
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uptake by plant including mycorrhizal symbiosis, especially under high P concentration,
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accompanying cations with phosphate onions and production of hydrogen onion (Miransari,
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2012).
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Usually high amounts of unavailable P are found in the soil, which is due to fertilization overuse.
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For example in the Iranian farms, the amount of P determined in the soil has been twice as much
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as the necessary amounts for plant growth and yield production. In addition, the over application
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of ammonium phosphate and triple super phosphate during the past three decades, has resulted in
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the pollution of soils, especially the paddy soils with cadmium. It has also resulted in the
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significant decrease of Zn in the soil and the rice grains (Sharma and Prasad, 2003).
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Zn deficiency is common in low land rice (Yang et al., 1994). High amounts of P in the paddy
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fields result in rice stunting due to P toxicity, inhibiting the uptake of micro-nutrients such as
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iron, zinc and boron by plant. Extra amounts of P can affect Zn mobility and accessibility by
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plant through limiting Zn transfer from the root to the shoot, decreasing Zn concentration in the
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soil solution, Zn binding by phytate and transfer of P through the cell membrane. In the paddy
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fields, use of P fertilization can decrease Zn uptake by plant through the production of
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phosphate-metal compounds (Dwivedi et al., 2003).
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In paddy soils P fertilization decreases Zn uptake by plant even in the case of Zn fertilization,
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which is due to Zn absorbance by iron oxides, and amorphous manganese under saturated
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conditions. Zn deficiency in the soil or its unavailability to plant significantly decreases crop
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yield as well as grain Zn concentration. If the soil is slightly deficient in P or Zn, adding one of
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the nutrients result in the deficiency of the other one, which can be compensated by fertilizing
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both nutrients (Barben et al., 2010).
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Accordingly, we studied how the application of Zn chelate sulfate may affect P and Zn behavior
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in a paddy field and in the rice plants (straw and grain). It is because of the chemical and
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physiological behavior of the two nutrients, which can adversely affect their uptake. These
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measurements can be important for grain fortification, which is of nutritional values for human
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health. Such kind of nutrient interaction can also be of importance for designing a balanced
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fertilization strategy for plant use with respect to environmental and economical aspects.
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Materials and methods
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The experiment was a completely randomized block design with four replicates conducted in
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2010, in the Rice Research Station, Tonekabon, Iran, located at 40o and 50’ altitude and 36o and
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54’ longitude, -20 m above the sea level. The average temperature and rainfall are equal to 15.8
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o
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used in the experiment, under a rice-rice cropping system, was ‘Shiroodi’. Thirty-day-old
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seedlings were transplanted to 3 x 6 m plots, separated by bunds. The transplantation (in four
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replicates) and harvesting of rice was done on May and September, respectively. Before planting,
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the experimental soil (loamy silt) was analysed for different parameters (Table 1). Soil pH was
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measured in the saturated paste using the glass electrode, total (10 mg/kg) and available P was
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determined using the Olsen’s method (Olsen, 1954) and the soil Zn was determined using DTPA
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method (Lindsay and Norwell, 1978).
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The basal dose of NPK at 120-90-60 kg ha along with Zn levels were applied in the form of
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urea, triple super phosphate (TSP), K2O and zinc sulphate, respectively. All P, K, Zn (applied to
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the soil) and half of the N was applied at the sowing stage and the remaining N was applied
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before flowering. The foliraly applied Zn fertilizer was a liquid formulation derived from ZnSO4
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according to the label containing some EDTA. The foliar application of zinc sulfate chelate was
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performed using control, 2, 4, 6 and 8 mg/L treatments three times at: 1) one month after
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transplant, 2) after full flowering, and 3) at the milky stage. The other practices were done
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according to the farmers in the region.
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The soil, grain, and leaf samples, collected at the spike/panicle initiating stage, were analyzed in
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the laboratory of the Rice Research Institute, Rasht to determine their available Zn concentration.
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The dry digestion method (HCl 2N) was used to digest the 10-g soil samples and using 0.005M
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DTPA-extractable solution and the atomic absorption spectrophotometer (Chemtech Alfa-4,
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Germany), their Zn contents were determined (Lindsy and Norvel, 1978).
C and 1253 mm, respectively. The air moisture is in the range of 74 to 92%. The rice cultivar
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Grain Zn was determined using the method of ASTM (ASTM, 2000; Lahive et al., 2011). Two
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grams of milled rice grain was heated at 105 oC for 48 hours. The samples were then digested
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using nitric and perchloric acid and one gram of each sample was treated with 2.5 mg sulfuric
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acid. The samples were mixed using a mixer for 30 minutes and were washed with acid and
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placed in a warm environment and the temperature was gradually increased to the boiling until
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the perchloric solution was evaporated. Deionized distilled water was used to bring up the
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solution volume to 25 ml. Using atomic absorption spectrometry (Chemtech Alfa-4, Germany)
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the grain Zn concentration (mg/kg) was determined.
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After harvesting all the grain samples were de-husked manually, and weighed for their hulls and
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brown rice. The 0.5 g rice flour samples were digested in a mixed compound of 2.0 ml 100%
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HNO3 and 0.5 ml 100% H2O2. The digesting solution was allowed to cool down to the room
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temperature (~25°C) and was then transferred into a 25 ml Erlenmeyer flask and brought up to
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the volume using distilled deionized water. Phosphorous concentration was then determined in
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the plant and grain samples according to Jones and Case (1990).
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Plant samples were washed initially by tap water followed by diluted hydrochloric acid (0.05),
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deionized water and Zn free double distilled water. The samples were then digested with triacid
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mixture: HNO3:HCLO4: H2SO4 (with the ratio of 10:4:1) to analyze their tissue Zn content
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(Jackson, 1973). At harvest, the yield of rice grain was recorded from each plot and analysed for
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total Zn described by Jackson (1973). Data were analysed using MSTAT C and SPSS. Mean
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comparison was performed according to Duncan’s method at P= 0.05.
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Results
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Effects of Zn foliar application on the P content of soil, straw and grain
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Application of Zn chelate significantly affected the P content of soil and rice straw and grain
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related to the control treatment (Table 2). The highest soil P content was related to the control
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treatment (28.13 mg/kg) followed by the other treatments, respectively. There were significant
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differences between treatment 2, 3 and 4 and 5. The highest concentration of straw P (11.85%)
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and grain P (0.98%) was related to the control treatment, followed by treatments 2, 3, 4 and 5,
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which were not significantly different from each other (Table 3).
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Effects of Zn foliar application on the Zn content of soil, straw and grain
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Zn treatments significantly affected the Zn content of soil, straw and grain. The highest (1.295
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mg/kg) and the lowest (0.322 mg/kg) content of soil Zn was related to treatment 5 and the
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control treatment, respectively, significantly different from the other treatments. There was also a
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similar trend for the straw and grain Zn. In the case of straw, the significant effects of treatments
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highly increased the straw Zn content significantly different from each other and from the
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control. The lowest Zn content was related to the control treatment (13.34 mg/kg) and the highest
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to treatment 5 (64.58 mg/kg) (Tables 4 and 5).
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For the grain Zn content although there was significant effect of treatments on Zn content, the
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differences were not as high as the differences related to Zn straw content. Treatments 3, 4 and 5
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were significantly different from the control treatment (the lowest at 8.94 mg/kg) and treatment
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2, however, treatment 3, 4, and 5 were not significantly different from each other (the highest at
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18.48 mg/kg) (Tables 4 and 5).
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Discussion
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P and Zn are two important nutrients, necessary for plant growth and yield production. However,
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due to their chemical and physiological properties there are always antagonistic effects between
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the two nutrients. In addition to the direct interactions between P and Zn, the adverse effects of P
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on plant Zn, when overused, appear by affecting Mn behavior (Barben et al., 2010; Nawaz et al.,
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2012). It is important to indicate how such kind of interactions may affect plant response as well
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as the translocation of the nutrient in different parts of the plant. Accordingly, in addition to the
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soil, P and Zn in rice straw and grain were also determined in this research work.
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Plant requirements for nutrients differ at different growth stages including the vegetative and
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reproductive ones. Hence, the application of Zn chelate was performed before seeding (to the
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soil) and at three different growth stages (foliarly) including: 1) right after the second transplant,
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2) after the full flowering, and 3) at the milky stage, which are also indicators of plant
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physiological properties (Chen et al., 2013). Zinc application significantly affected soil and plant
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P uptake. Hence, although there might have been some confounding effects between the method
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of Zn application, it is likely to adjust plant P uptake by using Zn fertilization. This can be a very
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important strategy to supply the necessary amounts of P for plant use.
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Measuring soil parameters (Table 1) can be useful for the proper determination of nutrients for
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plant growth. Accordingly, with respect to the amount of available P and Zn in the soil it is
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possible to indicate the amount of optimum fertilization for crop production. Considering
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nutrients in both soil and plant can more precisely contribute to the proper fertilization
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application. However, in paddy soils the conditions are different as most of the times the soil is
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saturated with water. Accordingly, the amounts of oxygen decease significantly, affecting the
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availability of nutrients as well as soil pH. Foliar application, especially for micro-nutrients is a
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suitable way of supplying plants with their necessary nutrients. It is because nutrients in the soil
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are subjected to fluctuating pH, moisture, oxygen, temperature, etc. affecting their availability
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and hence their uptake by plant (Obrador et al., 2003).
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With increasing the amount of Zn, soil P decreased significantly. This can be related to the
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production of chemical, which can fix P at significant amount. Straw and grain P concentration
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also decreased with higher rate of Zn, which can be attributed to the precipitation of P
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compounds in plant and production of phytates. Zn treatment increased the concentration of Zn
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in the soil, straw and grain. This can be a suitable method for the enrichment of rice grain with
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Zn (Cakmak et al., 2010; Yosefi et al., 2011). However, it is also important to indicate the
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appropriate amounts of Zn so that the plant can also absorb the optimum rate of P.
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There are different factors affecting the interaction between P and Zn and hence their uptake
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including soil, plant and climate parameters. Modifying the adjustable parameters can result in a
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more efficient uptake of Zn by plant (Hacisalihoglu and Kochian, 2003; Li et al., 2010). For
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example, root exudates such as organic acids, root morphology and plant physiology, soil
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microbes, soil structure and texture as well as the amount of rain can significantly affect the
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uptake of nutrients such as P and Zn by plant (Miransari and Mackenzie 2011; Miransari 2011a,
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b). Accordingly, it is possible to genetically modify plant characters in a way, which may result
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in a higher utilization and uptake of nutrients by plant (Hacisalihoglu and Kochian, 2003; Rose et
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al., 2011). The use of efficient cultivars is also a proper way for the increased utilization and
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hence uptake of Zn by plant (Rasouli-Sadaghiani et al., 2011).
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Conclusion
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In the presented research work the effects of Zn (applied foliarly and to the soil) on the amounts
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of P and Zn in the soil and rice straw and grain were investigated in a paddy field. Application of
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Zn significantly decreased P concentration in the soil as well as P uptake by rice straw and grain.
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Although there might have been some confounding effects between the methods of application,
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the results indicated that Zn application significantly affected P behavior in the soil and in the
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plant. Considering such kind of interactions, which are resulted by the chemical and
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physiological properties of the two nutrients, can be useful for the proper determination of
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fertilization rate. Although Zn is important for the grain fortification, it must be applied at an
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appropriate rate, which can also result in the P optimum uptake. The other important point about
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this research work is the foliar use of Zn chelate at three different stages, which is useful for
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evaluating nutrient behavior during plant growth and crop production.
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Table 1. Analysis of soil properties before planting
Organic matter (%)
N (%)
pH
EC (dS/m)
6.82
0.34
7.64
0.53
Available P (mg/kg)
S (mg/kg)
SO42-
Ca (meq/l)
3.88
137.3
412
7.68
Fe (mg/kg)
Zn (mg/kg)
Mn (mg/kg)
Cu (mg/kg)
32
0.4
18.12
4.95
323
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325
326
327
328
329
330
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Table 2. Analysis of variance related to the P content of soil and rice straw and grain (Shiroodi cultivar) as affected
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by Zn application.
Source of variation
d.f.
Soil P
Straw P
Grain P
Block
3
3.468n.s.
0.958n.s.
0.062n.s.
Treatment
4
37.925**
12.415**
0.274**
Experimental error
12
0.075
0.895
0.026
Total
19
1.18
11.03
28.33
Coefficient of variation
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n.s., *, **, ***: non-significant, significant at 1, 5 and 0.1% level of probability, respectively.
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Table 3. Mean comparison of P content of soil and rice straw and grain (Shiroodi cultivar) as affected by Zn
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application.
Treatment
Soil P (mg/kg)
Straw P (%)
Grain P (%)
Control
28.13a
11.85a
0.98a
Treatment 2
23.94b
8.82b
0.75b
Treatment 3
21.88c
7.60b
0.65b
Treatment 4
20.88d
7.75b
0.57b
Treatment 5
20.75d
7.35b
0.75b
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350
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353
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Table 4. Analysis of variance related to the Zn content of soil and rice straw and grain (Shiroodi cultivar) as affected
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by Zn application.
Source of variation
d.f.
Soil Zn
Straw Zn
Grain Zn
Block
3
0.057n.s.
11.561n.s.
1.390n.s.
Treatment
4
0.507**
2168.329**
56.752**
Experimental error
12
0.029
3.273
0.661
Total
19
22.90
4.54
5.31
Coefficient of variation
359
360
361
362
363
364
365
366
367
368
17
369
370
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Table 5. Mean comparison of Zn content of soil and rice straw and grain (Shiroodi cultivar) as affected by Zn
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application.
Treatments
Soil Zn (mg/kg)
Straw Zn
Grain Zn
(mg/kg)
(mg/kg)
Control
0.322c
13.34e
8.94d
Treatment 2
0.587b
17.10d
15.10c
Treatment 3
0.770b
47.65c
16.56b
Treatment 4
0.762b
56.48b
17.44ab
Treatment 5
1.295a
64.58a
18.48a
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374
375
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