MATERIALS AND METHODS

Pot experiment was conducted in the greenhouse of the project "Micronutrients", Department of Fertilization Technology, National Research Centre, Dokki, Cairo, Egypt with wheat (Triticum aestivum L.) variety Sakha 93 to study the effect of magnesium sulphate as soil amendments and foliar feeding with magnesium sulphate diluted solutions on the dry weight accumulation, plant height and nutrient concentrations, uptake and balance within the shoot tissues.

The experiment followed the Completely Randomized Block Design (CRBD) with eight treatments in four replicates. The plants were sown on the end of October, 2011 in Mitscherlich pots contained 7.0 kg loamy sand soil. Before sowing, every pot was received 1.05 g urea (46% N), 1.4 g super mono-phosphate (15.5% P₂O₅) and 0.35 g potassium sulphate (50% K₂O) as basic fertilization.

Treatments
Soil amendments:

Foliar fertilization: The plants were two times sprayed at 25 days after sowing and two weeks later as follows:

Harvest: Two months after sowing, the plant height was measured and the plants were harvested to determine dry matter accumulation in the shoots as well as macro and micronutrient concentrations. Then the nutrient uptake was accordingly calculated.

Determinations and measurements
Soil: Representative soil sample before fertilization was air-dried and passed through 2-mm sieve pores. Soil fractions were determined using the hydrometer method (Bauyoucos, 1954). E.C. and pH were determined in a soil/water extract (1:2.5) according to Jackson (1973). The CaCO₃ content was determined using the calcimeter method according to Black (1965). Organic matter was determined using the potassium dichromate method according to Walkely and Black (1934). Soil P was extracted using sodium bicarbonate (NaHCO₃) (Olsen et al., 1954). K was extracted using ammonium acetate (C₃H₃O₂NH₄) (Chapman and Pratt, 1978). Fe, Mn, Zn and Cu were extracted using DTPA-solution (Lindsay and Norvell, 1978). Chemical and physical properties of the soil are shown in Table 1.

Vegetative tissue: Samples were washed with tap water, 0.01 N HCl and bi-distilled water, respectively, dried at 70°C for 24 h, weighed and ground. A part of the dry leaves was ashed in a Muffle furnace at 550°C for 6 h. The ash was digested in 3 N HNO₃ and the residue was then suspended in 0.3 N HCl (Chapman and Pratt, 1978).

Table 1:	Chemical and physical characteristics of the used soil
H: High, M: Medium, L: Low, VL: Very low Ankerman and Large (1974)

Nutrient measurements: Nitrogen was determined using Micro-Kjeldahl method digestion and titration method (Ma and Zauzage, 1942). Phosphorus was photometrical determined using the molybdate-vanadate method. Potassium, sodium and calcium were measured using Dr. Lang -M8D Flame-photometer. Magnesium, Fe, Mn, Zn and Cu were determined using the Atomic Absorption Spectrophotometer (Perkin-Elmer 100 B).

Evaluation of the nutrient status: Soil nutrient concentrations were evaluated according to the tentative values of Ankerman and Large (1974) and shoot tissue nutrient concentration ratios were based upon the values of Reuter (1986).

Statistical analysis: Data were subjected to statistical analysis as specified by Snedecor and Cochran (1990). Treatment means were calculated and subjected to the one-way ANOVA analysis and Student-Newman Keuls (SNK) and LSD (p≤0.05) tests-multiple comparison of means, using Costate 2 Program (Cohort software) for different treatments.

RESULTS AND DISCUSSION

The used soil (Table 1), as most of the Egyptian soils is characterized by high pH value, low organic matter content and poverty of macro and micronutrients. It is well known that magnesium is in competition with other major cations in the soil such as calcium (Ca⁺⁺), potassium (K⁺), sodium (Na⁺), ammonium (NH⁺₄), iron (Fe⁺⁺) and aluminum (Al⁺⁺⁺) and potassium is the stronger competitor with Mg. So, Intensive agriculture used high rates of potassium and ammonium fertilizers and neglecting of Mg-fertilization led to Mg-unavailability which became a limiting growth factor (El-Fouly et al., 2010).

Magnesium sulphate effect on nutrient concentrations and balance: Data in Table 2 and 3 showed significant increase of N, Ca, Mg, Na, Fe and Cu concentrations in the shoot tissues due to MgSO₄ soil amendment or foliar fertilization. The best treatment was the rate 120 Kg ha^-1 as soil amendment or 5 g L^-1 in the spray solution as foliar fertilization. This may attributed to adjusting of the nutrient balance in the shoot tissues (Fig. 1). Nutrient ratios Mg/P, K/Mg and Ca/Mg of both treatments ranked to the middle of the ideal range which realized best assimilation of Mg to play its role in the control and uptake of nutrients and its role as activator for many enzymatic processes in the plant tissues (Marschner, 1995).

Fig. 1:	Nutrient balance within shoot tissues treated with MgSO4 soil amendment foliar fertilization

Table 2:	Effect of MgSO4 soil amendment or foliar fertilization on macronutrients concentration
Columns with the same letters are not significantly different at LSD 0.05, N.S: Not significant

Magnesium found also to enhance stomatal width, length and transpiration rate which may encourage the passive uptake of nutrients (Putra et al., 2012). Similar findings regarding the increase in the uptake of nutrients by wheat straw when sprayed with magnesium were also reported by El-Metwally et al. (2010).

Magnesium sulphate effect on nutrient uptake: Both MgSO₄ soil amendment and foliar fertilization had positive significant effects on the nutrient uptake of the determined macro and micronutrients (Table 4 and 5).

Table 3:	Effect of MgSO4 soil amendment or foliar fertilization on micronutrients Concentration
Columns with the same letters are not significantly different at LSD 0.05 NS: Not significant

Table 4:	Effect of MgSO4 soil amendment or foliar fertilization on macronutrients uptake
Columns with the same letters are not significantly different at LSD 0.05

Superior treatments were also the rate 120 Kg ha^-1 as soil amendment or 5 g L^-1 in the spray solution as foliar fertilization. Same trend was found by Bohri et al. (2000) who determined the effect of Mg fertilization on the rice plants grown on artificial siltation soil. According to his results, the uptake of all nutrients in the straw was increased with Mg treatments. Magnesium positive effect on nutrients uptake may relate to its role in enzymatic processes activation and increase of nitrogen and iron utilization by the plants (Marschner, 1995).

Magnesium sulphate effect on plant growth: Growth of wheat plants interpreted as dry weight accumulation (g plant^-1) and plant height (cm) is shown in Fig. 2 and 3, respectively. The treatment equal 60 Kg ha^-1 as soil amendment or 5.0 g L^-1 in the spray solution as foliar fertilization were sufficient to realize most significant dry weight and plant height increases. Positive effect of Mg on dry biomass accumulation and plant height can be attributed to its role in photosynthesis, as a carrier of phosphorus, improvement of nutrient uptake, sugar synthesis and starch translocation (Marschner, 1995).

Fig. 2:	Dry biomass accumulation in wheat shoots as affected by MgSO4 soil amendment or foliar fertilization, Columns with same letters are not significantly different at p = 0.05

Fig. 3:	Wheat plant height as affected by MgSO4 soil amendment or foliar fertilization, Columns with same letters are not significantly different at p = 0.05

Table 5:	Effect of MgSO4 soil amendment or foliar fertilization on micronutrients uptake
Columns with the same letters are not significantly different at LSD 0.05

Sabo et al. (2002) concluded that winter wheat genotypes assimilated 80-130 kg ha^-1 from the soil and thus Mg availability from the soil could significantly influence dry matter accumulation and crop productivity. Similar findings were also reported by Tan et al. (1992) with sorghum. Dhiraj and Kumar (2012) concluded that foliar nutrients increases crop quality and yield. Upadhyay and Patra (2011) found that 200 mg Mg pot^-1 significantly increased plant height, number of branches per plant, width of flower, number of flower per plant, fresh weight and oil content of chamomile plants.

CONCLUSIONS

From the present findings it can be concluded that:

ACKNOWLEDGMENTS

The authors wish to thank the staff members of the program "Micronutrients and Plant Nutrition Problems" and its principal investigator Prof. Dr. Mohamed M. El-Fouly for providing work facilities.