Indian Journal of Agronomy

How the application of zinc sulfate chelate may affect phosphorous uptake by rice (Oryza sativa L.) plant

H. Hossein Zadeh1, M. Mablaghi2, S. Mashayekhi1, N. Divsalar2, A.P. Salehi2, M. Miransari3*

1: Islamic Azad University, Science and Research Branch, Department of Agronomy, Tehran, Iran

2: Islamic Azad University, Chalus Branch, Iran

3*: Corresponding author, Prof. Dr. Mohammad Miransari: 1) Mehrabad Rudehen, Imam Ali Blvd., Mahtab Alley, #55, Postal number: 3978147395, Tehran, Iran, E-mail: , 2) AbtinBerkeh Limited Co., Imam Blvd., Shariati Blvd. # 107, Postal number: 3973173831, Rudehen, Tehran, Iran, Telfax: (98)2176506628, Mobile: (98)9199219047, E-mail:

Abstract

For rice plants to obtain high yields, optimum amounts of nutrients must be supplied at different growth stages. However, there are usually positive or negative interactions between nutrients such as zinc (Zn) and phosphorus (P). Using Zn sulfate chelate, a completely randomized block design experiment with four replicates was performed in 2010 at Tonekabon Rice Research Station, Iran, to test the uptake of Zn and P by rice (Oriza sativa L.). Ninety kilograms of phosphate fertilization was applied to the soil before seeding. Zinc chelate sulfate was applied to the soil before seeding and foliarly (control, 2, 4, 6 and 8 mg/l), one month after transplanting, after full flowering, and at the milky stage. The highest and lowest amounts of P in the soil and rice straw and grain were related to the control and 8 mg/L treatments, respectively indicating that there were significantly adverse interactions between the two nutrients.

Key words: Antagonistic effects, chelate of zinc sulfate, phosphorus, rice (Oriza sativa L.), growth stages

Introduction

It is important to use the optimum amount of fertilization for crop production, because otherwise it would have unfavorable economical and environmental consequences. Although chemical fertilization has been successfully used for rice production during the past three decades, its unbalanced use has adversely affected the environment including the soil (Sedri and Malakouti, 1999). The increased concentration of nitrate in the ground water and cadmium in the paddy fields and rice grains are among such adverse effects (Miransari and Mackenzie, 2010).

Zinc (Zn) is among the most important micro-nutrients necessary for different plant functioning including the production of proteins and nucleic acids. Zn translocation is complicated in the plant and it is very limited in the phloem (Liu et al., 2003). Zn is also necessary for plant metabolism including plant enzymatic activities, production of carbohydrates, proteins, auxin and reproduction processes. For example, Zn is necessary for the production of 60 plant enzymes and among its important functions its role in the structure of tryptophan as the prerequisite for the production of auxin is also of significance (Simmons et al., 2003).

The important point about nutrient uptake by a plant is their availability to the plant. The importance of soil factors such as pH, salinity, structure, moisture, biological activities, etc. play a significant role on the availability of nutrients. For example, in calcareous soil, the solubility and hence availability of micro-nutrients including Zn decrease significantly. Zinc deficiency is very common in paddy soils with acidic pH as well as in the soils with acidic pH and high P concentration (Norman et al., 2003). The effects of soil pH on root and microbial activities can also influence the availability of soil nutrients. Accordingly, the use of foliar application, especially for micronutrients, has become common as it increases the utilization efficiency of micronutrients by plant (Marschner, 1995; Miransari, 2012).

Phosphorus (P) is also an essential element for different plant functions. The most important function of P in plant is the storage and transfer of energy as well as the membrane stability at different growth stages. The critical level of P in the soil using the Olsen’s method is 5 mg/kg in acidic soils, which is also subjected to immediate fixation by soil particles (Marschner, 1995).

According to Marschner (1995) parameters such as Zn content, dilution effect, as well as P availability in the soil affect Zn uptake by plants. Under tropical conditions, due to P fertilization and use of lime, Zn deficiency is intensified. There are some other parameters affecting Zn uptake by plant including mycorrhizal symbiosis, especially under high P concentration, accompanying cations with phosphate onions and production of hydrogen onion (Miransari, 2012).

Usually high amounts of unavailable P are found in the soil, which is due to fertilization overuse. For example in the Iranian farms, the amount of P determined in the soil has been twice as much as the necessary amounts for plant growth and yield production. In addition, the over application of ammonium phosphate and triple super phosphate during the past three decades, has resulted in the pollution of soils, especially the paddy soils with cadmium. It has also resulted in the significant decrease of Zn in the soil and the rice grains (Sharma and Prasad, 2003).

Zn deficiency is common in low land rice (Yang et al., 1994). High amounts of P in the paddy fields result in rice stunting due to P toxicity, inhibiting the uptake of micro-nutrients such as iron, zinc and boron by plant. Extra amounts of P can affect Zn mobility and accessibility by plant through limiting Zn transfer from the root to the shoot, decreasing Zn concentration in the soil solution, Zn binding by phytate and transfer of P through the cell membrane. In the paddy fields, use of P fertilization can decrease Zn uptake by plant through the production of phosphate-metal compounds (Dwivediet al., 2003).

In paddy soils P fertilization decreases Zn uptake by plant even in the case of Zn fertilization, which is due to Zn absorbance by iron oxides, and amorphous manganese under saturated conditions. Zn deficiency in the soil or its unavailability to plant significantly decreases crop yield as well as grain Zn concentration. If the soil is slightly deficient in P or Zn, adding one of the nutrients result in the deficiency of the other one, which can be compensated by fertilizing both nutrients (Barben et al., 2010).

Accordingly, we studied how the application of Zn chelate sulfate may affect P and Zn behavior in a paddy field and in the rice plants (straw and grain). It is because of the chemical and physiological behavior of the two nutrients, which can adversely affect their uptake. These measurements can be important for grain fortification, which is of nutritional values for human health. Such kind of nutrient interaction can also be of importance for designing a balanced fertilization strategy for plant use with respect to environmental and economical aspects.

Materials and methods

The experiment was a completely randomized block design with four replicates conducted in 2010, in the Rice Research Station, Tonekabon, Iran, located at 40o and 50’ altitude and 36o and 54’ longitude, -20 m above the sea level. The average temperature and rainfall are equal to 15.8 oC and 1253 mm, respectively. The air moisture is in the range of 74 to 92%. The rice cultivar used in the experiment, under a rice-rice cropping system, was ‘Shiroodi’. Thirty-day-old seedlings were transplanted to 3 x 6 m plots, separated by bunds. The transplantation (in four replicates) and harvesting of rice was done on May and September, respectively. Before planting, the experimental soil (loamy silt) was analysed for different parameters (Table 1). Soil pH was measured in the saturated paste using the glass electrode, total (10 mg/kg) and available P was determined using the Olsen’s method (Olsen, 1954) and the soil Zn was determined using DTPA method (Lindsay and Norwell, 1978).

The basal dose of NPK at 120-90-60 kg ha-1 along with Zn levels were applied in the form of urea, triple super phosphate (TSP), K2O and zinc sulphate, respectively. All P, K, Zn (applied to the soil) and half of the N was applied at the sowing stage and the remaining N was applied before flowering. The foliraly applied Zn fertilizer was a liquid formulation derived from ZnSO4 according to the label containing some EDTA. The foliar application of zinc sulfate chelate was performed using control, 2, 4, 6 and 8 mg/L treatments three times at: 1) one month after transplant, 2) after full flowering, and 3) at the milky stage. The other practices were done according to the farmers in the region.

The soil, grain, and leaf samples, collected at the spike/panicle initiating stage, were analyzed in the laboratory of the Rice Research Institute, Rasht to determine their available Zn concentration. The dry digestion method (HCl 2N) was used to digest the 10-g soil samples and using 0.005M DTPA-extractable solution and the atomic absorption spectrophotometer (Chemtech Alfa-4, Germany), their Zn contents were determined (Lindsy and Norvel, 1978).

Grain Zn was determined using the method of ASTM (ASTM, 2000; Lahive et al., 2011). Two grams of milled rice grain was heated at 105 oC for 48 hours. The samples were then digested using nitric and perchloric acid and one gram of each sample was treated with 2.5 mg sulfuric acid. The samples were mixed using a mixer for 30 minutes and were washed with acid and placed in a warm environment and the temperature was gradually increased to the boiling until the perchloric solution was evaporated. Deionized distilled water was used to bring up the solution volume to 25 ml. Using atomic absorption spectrometry (Chemtech Alfa-4, Germany) the grain Zn concentration (mg/kg) was determined.

After harvesting all the grain samples were de-husked manually, and weighed for their hulls and brown rice. The 0.5 g rice flour samples were digested in a mixed compound of 2.0 ml 100% HNO3 and 0.5 ml 100% H2O2. The digesting solution was allowed to cool down to the room temperature (~25°C) and was then transferred into a 25 ml Erlenmeyer flask and brought up to the volume using distilled deionized water. Phosphorous concentration was then determined in the plant and grain samples according to Jones and Case (1990).

Plant samples were washed initially by tap water followed by diluted hydrochloric acid (0.05), deionized water and Zn free double distilled water. The samples were then digested with triacid mixture: HNO3:HCLO4: H2SO4 (with the ratio of 10:4:1) to analyze their tissue Zn content (Jackson, 1973). At harvest, the yield of rice grain was recorded from each plot and analysed for total Zn described by Jackson (1973). Data were analysed using MSTAT C and SPSS. Mean comparison was performed according to Duncan’s method at P= 0.05.

Results

Effects of Zn foliar application on the P content of soil, straw and grain

Application of Zn chelate significantly affected the P content of soil and rice straw and grain related to the control treatment (Table 2). The highest soil P content was related to the control treatment (28.13 mg/kg) followed by the other treatments, respectively. There were significant differences between treatment 2, 3 and 4 and 5. The highest concentration of straw P (11.85%) and grain P (0.98%) was related to the control treatment, followed by treatments 2, 3, 4 and 5, which were not significantly different from each other (Table 3).

Effects of Zn foliar application on the Zn content of soil, straw and grain

Zn treatments significantly affected the Zn content of soil, straw and grain. The highest (1.295 mg/kg) and the lowest (0.322 mg/kg) content of soil Zn was related to treatment 5 and the control treatment, respectively, significantly different from the other treatments. There was also a similar trend for the straw and grain Zn. In the case of straw, the significant effects of treatments highly increased the straw Zn content significantly different from each other and from the control. The lowest Zn content was related to the control treatment (13.34 mg/kg) and the highest to treatment 5 (64.58 mg/kg) (Tables 4 and 5).

For the grain Zn content although there was significant effect of treatments on Zn content, the differences were not as high as the differences related to Zn straw content. Treatments 3, 4 and 5 were significantly different from the control treatment (the lowest at 8.94 mg/kg) and treatment 2, however, treatment 3, 4, and 5 were not significantly different from each other (the highest at 18.48 mg/kg) (Tables 4 and 5).

Discussion

P and Zn are two important nutrients, necessary for plant growth and yield production. However, due to their chemical and physiological properties there are always antagonistic effects between the two nutrients. In addition to the direct interactions between P and Zn, the adverse effects of P on plant Zn, when overused, appear by affecting Mn behavior (Barben et al., 2010; Nawaz et al., 2012). It is important to indicate how such kind of interactions may affect plant response as well as the translocation of the nutrient in different parts of the plant. Accordingly, in addition to the soil, P and Zn in rice straw and grain were also determined in this research work.

Plant requirements for nutrients differ at different growth stages including the vegetative and reproductive ones. Hence, the application of Zn chelate was performed before seeding (to the soil) and at three different growth stages (foliarly) including: 1) right after the second transplant, 2) after the full flowering, and 3) at the milky stage, which are also indicators of plant physiological properties (Chen et al., 2013). Zinc application significantly affected soil and plant P uptake. Hence, although there might have been some confounding effects between the method of Zn application, it is likely to adjust plant P uptake by using Zn fertilization. This can be a very important strategy to supply the necessary amounts of P for plant use.