THE ROLE OF MAGNESIUM IN INCREASING OF PHOSPHORUS FERTILIZER EFFICIENCY AND WHEAT YIELD

The study was conducted during the growing season 2003 to study the influence of four levels of P (0, 60, 100 and 140 kg ha) and four levels of Mg (0, 40, 80 and 120 kg ha) at two locations (Bakrajow and Kalar) on growth and yield of wheat and phosphorus fertilizer efficiency. The results indicated to the response of wheat to phosphorous fertilizer at Bakrajow location only. While the application of 40 kg Mg ha caused significant increase in wheat yield at Bakrajow location only. The highest phosphorus fertilizer efficiency was 34.44% and 55.24% at Bakrajow and Kalar respectively while the Mg fertilizer efficiency was 7.6% and 22.8% at Kalar and Bakrajow respectively. INTRODUCTION There are many factors influencing phosphorus availability, efficiency and recovery of phosphorus fertilizer by plants like soil pH, texture, type of clay minerals, calcium carbonate content of the soil, organic matter content of the soil and Mg/Ca ratio of irrigation water or soil solution in additional to mycorhizal activity (Foth, et al., 2000; AlAkrawi, 2002). Magnesium plays a positive role in phosphorus availability and recovery of phosphorus by crops in calcareous soil like magnesium concentration in soil solution. Magnesium can alter the formation of calcium phosphate precipitates and apatite formation (Marin and Babcok, 1977). On the other hand Kuo and Milkkelsen (1977) showed that magnesium may interfere with phosphorus adsorption on CaCO3 surface by one of the following mechanisms: 1-Magnesium that alters some of adsorption sites on CaCO3 surface, due to lower affinity of phosphate to Mg in comparing with Ca which causes the decrease in phosphorus adsorption by CaCO3. 2-The extend to which magnesium will affect the availability of phosphorus depends on the mole ratio of P/Mg, if the ratio is equal or less than 2:1 the efficiency of phosphorus will increase due to the reduction in adsorption of phosphorus by CaCO3 which causes increase of available phosphorus in calcareous soil, since the solubility of magnesium orthophosphate slightly higher than the solubility of calcium orthophosphate. Dawood (1982) indicated that the application of three levels (0,120 and 240kg MgSO4.7H2O ha ) caused a significant increase in phosphorus uptake by plant. Al-Lami (1999) showed that the increase in adding of MgSO4.7H2O from 0 to 80 kg ha -1 caused a significant increase in available phosphorus in the soil from 0.23 to 0.25 cmolc kg . Mesopotamia J. of Agric. (ISSN 1815 – 316 X) Vol.(39) No.(2) 2011 34 On the other hand the Mg/Ca ratio plays an important role in phosphorus availability. Madrid, et al.(1977) showed that the increase in utilization efficiency Received 10/5/2009 accepted 20/9/ 2010 of phosphorus fertilizer by rye grass as the ratio of Mg/Ca increased by the incorporation of MgSO4.7H2O with dicalocium phosphate and octacalcium phosphate. Al-Khatteb et al.(1986) found the formation of higher amount of dimagnesium phosphate and trimagnesium phosphate, if the ratio of Mg/Ca higher than 1.5 which caused the increase in phosphorus availability. Al-Kaysi and Saleem (1990) applied different ratios (0/0, 0/200, 50/150, 100/100, 150/50, 200/0 meq L) 0f Mg/Ca they indicated that the increase in the ratio of applied Mg/Ca caused an increase in phosphorus availability for plants. Esmail (1992); Dohuki (1997); Abbod (1998) and Esmail, et al.(1999) indicated that the increase in Mg/Ca to 1.5 in soil solution and irrigation water caused a significant increase in available phosphorus in the soil and its recovery by plant. Al-Akrawi (2002) studied the influence of four levels (0, 40, 80, 120 kg Mg ha) of Mg on the efficiency of phosphorus fertilizer by using three levels of triple superphosphate (0, 100, 200 kg P ha) she found that the application of 120 kg ha of Mg-fertilizer caused the conversion of phosphorus phase to more soluble from (DCPD) in comparing with control treatment (above OCP). For the mentioned reason the purpose of this study includes the role of Mgfertilizer in P-availability, growth and yield of wheat at two different locations. MATERIALS AND METHODS The experiment was conducted at two different locations ( Bakrajow and Kalar) under rain-fed condition during the winter growing season 2003 to study the influence of four levels of Mg as MgSO4.7H2O ( 0, 40, 80, 120 kg ha ) and four levels of P as TSP (0, 60, 100 and 140 kg ha) and their interaction on wheat yield ,availability of phosphorus and the efficiency of phosphorus and magnesium fertilizers using Randomized Complete Block Design (RCBD) with three replicates. 100kg N ha as urea fertilizer was added at the sowing time. On 20 and 24 November 2003 seeds of wheat variety Acsad were planted at Bakrajow and Kalar respectively. The plants from Kalar location were harvested on 26 may 2004 while at Bakrajow the harvesting was conducted on 1 June 2004. Soil samples were taken from all experimental units at (0 to 30 cm) depth before sowing and after harvesting, then air dried thoroughly mixed, ground passed through a 2 mm sieve, and stored in plastic bottles prior to analysis. Some physical and chemical properties of the soils are given in (table 1). Electrical conductivity (EC) was measured for the soil saturation extract using EC-meter, model (WTW 82362 Weilheim, Germany). pH was measured in a saturated peaste using a pH-meter, model (Microprocessor pH meter, Hanna pH 211).Organic matter was determined by dichromate oxidation (Walkley and Black method) as described in Jackson (1973).The total calcium carbonate equivalent CaCO3 was determined by a rapid titration method (Rayment and Higginson, 1992).Cation Exchange Capacity (CEC) was Mesopotamia J. of Agric. (ISSN 1815 – 316 X) Vol.(39) No.(2) 2011 35 determined by saturation with 1M NH4OAc at pH 8.1.Soluble HCO3 , Cl and Ca + Mg were determined using titration methods (Page et al., 1982).Na and K were determined by using (Flame Photometer). SO4 was indirectly determined from combined Ca and Mg by titration with (0.02M) EDTA disodium salt according to Jackson (1958). Available P was determined by extracting the samples with 0.5M NaHCO3 (Olsen et al., 1954). The particle size was determined according to international pipette method as described by Day (1965). Table (1): some physical and chemical properties of soil used in field experiments. Properties Location Particle Size Distribution(PSD) g kg Bakrajow Kalar Sand 115.4 234 Silt 523.6 572 Clay 361 196 Texture Class SiCL SiL pH 7.90 7.60 ECe dS m -1 at 25C 0.40 2.60 Soluble ions mmolc L -1 Ca 1.70 12.0 Mg 0.31 4.60 Na 0.48 4.20 K 0.19 6.10 HCO3 2.95 3.20 Cl 0.21 16.10 SO4 20.81 20.10 Cation Exchange capacity cmolc kg -1 29.76 22.10 O. M. g kg 17.6 7.57 Available P mg kg 6.5 9 CaCO3 equivalent g kg Total 328.00 370.3 Plant analysis: The representative harvested wheat shoots were dried at 65C for 72 hr dried plant material were grinded then digested according to Schuffelen and Schouwenburg(1961) using (1:1 conc.H2SO4 and H2O2)mixture to determination the concentration of phosphorus in digested plant samples according to colorimetric method as described by Rowell (1996). Biological parameters were calculated using the following models: Relative yield = (yield of control / yield of fertilized treatment) x 100............. (1) Response %=( yield fertilized – yield control) / yield fertilized x 100.............. (2) FUS = [{P-uptake (fertilized) – P-uptake (control)} / P-added] x 100...............(3) Mesopotamia J. of Agric. (ISSN 1815 – 316 X) Vol.(39) No.(2) 2011 36 According to Westerman, 1990 and Tisdale, et al., 1997. RESULTS AND DISCUSSION Influence of different levels of Mg and P fertilizer and their interaction on grain weight: Table (2) shows the significant effect of Mg, P and their interaction on grain yield at Bakrajow location, the highest values 5142.6, 5113.3 and 5605.2 kg ha were recorded from treatments, Mg1, P1 and Mg2P3 respectively. The above results indicated that the combination between Mg and P caused the decrease in P-fertilizer requirement for the highest yield.Table (3) indicated that the Mg, P-fertilizer and their interaction were no affected significantly on grain yield this may be due to the high concentration of Mg in Kalar soil (4.20 mmolc kg ) and high 1.2 ratio of Na/Ca ratio this may causes the increase in phosphorus availability the similar results were obtained by Esmail (1992). Table (2): Influence of different rates of Mg, P and their interaction on wheat grain yield (kg ha) at Bakrajow location. P Mg P0 P1 P2 P3 mean %Fertilizer efficiency Mg0 4690.0 4680.0 5085.2 5005.2 4865.1 0 Mg1 5205.2 5545.2 4930.0 4890.0 5142.6 22.8 Mg2 4650.0 4980.0 4805.2 5605.2 5010.1 12.0 Mg3 4440.0 5248.0 4920.0 5120.0 4932.0 5.6 mean 4746.0 5113.3 4935.2 4985.2 %Fertilizer efficiency 30.92 15.88 34.44 RLSD0.05 P = 101.2 RLSD0.05 Mg = 101.2 RLSD0.05 Mg x P = 212.8 Table (3): Influence of different rates of Mg, P and their interaction on wheat grain yield (kg ha) at Kalar location. P Mg P0 P1 P2 P3 mean %Fertilizer efficiency Mg


INTRODUCTION
There are many factors influencing phosphorus availability, efficiency and recovery of phosphorus fertilizer by plants like soil pH, texture, type of clay minerals, calcium carbonate content of the soil, organic matter content of the soil and Mg/Ca ratio of irrigation water or soil solution in additional to mycorhizal activity (Foth, et al., 2000;Al-Akrawi, 2002).Magnesium plays a positive role in phosphorus availability and recovery of phosphorus by crops in calcareous soil like magnesium concentration in soil solution.Magnesium can alter the formation of calcium phosphate precipitates and apatite formation (Marin and Babcok, 1977).On the other hand Kuo and Milkkelsen (1977) showed that magnesium may interfere with phosphorus adsorption on CaCO 3 surface by one of the following mechanisms: 1-Magnesium that alters some of adsorption sites on CaCO 3 surface, due to lower affinity of phosphate to Mg 2+ in comparing with Ca 2+ which causes the decrease in phosphorus adsorption by CaCO 3 .2-The extend to which magnesium will affect the availability of phosphorus depends on the mole ratio of P/Mg, if the ratio is equal or less than 2:1 the efficiency of phosphorus will increase due to the reduction in adsorption of phosphorus by CaCO 3 which causes increase of available phosphorus in calcareous soil, since the solubility of magnesium orthophosphate slightly higher than the solubility of calcium orthophosphate.Dawood (1982) indicated that the application of three levels (0,120 and 240kg MgSO 4 .7H 2 O ha -1 ) caused a significant increase in phosphorus uptake by plant.Al-Lami (1999) showed that the increase in adding of MgSO 4 .7H 2 O from 0 to 80 kg ha -1 caused a significant increase in available phosphorus in the soil from 0.23 to 0.25 cmol c kg -1 .

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On the other hand the Mg/Ca ratio plays an important role in phosphorus availability.Madrid, et al.(1977) showed that the increase in utilization efficiency Received 10/5/2009 accepted 20/9/ 2010 of phosphorus fertilizer by rye grass as the ratio of Mg/Ca increased by the incorporation of MgSO 4 .7H 2 O with dicalocium phosphate and octacalcium phosphate.Al-Khatteb et al.(1986) found the formation of higher amount of dimagnesium phosphate and trimagnesium phosphate, if the ratio of Mg/Ca higher than 1.5 which caused the increase in phosphorus availability.Al-Kaysi and Saleem (1990) applied different ratios (0/0, 0/200, 50/150, 100/100, 150/50, 200/0 meq L -1 ) 0f Mg/Ca they indicated that the increase in the ratio of applied Mg/Ca caused an increase in phosphorus availability for plants.Esmail (1992); Dohuki (1997); Abbod (1998) and Esmail, et al.(1999) indicated that the increase in Mg/Ca to 1.5 in soil solution and irrigation water caused a significant increase in available phosphorus in the soil and its recovery by plant.Al-Akrawi (2002) studied the influence of four levels (0, 40, 80, 120 kg Mg ha -1 ) of Mg on the efficiency of phosphorus fertilizer by using three levels of triple superphosphate (0, 100, 200 kg P ha -1 ) she found that the application of 120 kg ha -1 of Mg-fertilizer caused the conversion of phosphorus phase to more soluble from (DCPD) in comparing with control treatment (above OCP).For the mentioned reason the purpose of this study includes the role of Mgfertilizer in P-availability, growth and yield of wheat at two different locations.

MATERIALS AND METHODS
The experiment was conducted at two different locations ( Bakrajow and Kalar) under rain-fed condition during the winter growing season 2003 to study the influence of four levels of Mg as MgSO 4 .7H 2 O ( 0, 40, 80, 120 kg ha -1 ) and four levels of P as TSP (0, 60, 100 and 140 kg ha -1 ) and their interaction on wheat yield ,availability of phosphorus and the efficiency of phosphorus and magnesium fertilizers using Randomized Complete Block Design (RCBD) with three replicates.100kg N ha -1 as urea fertilizer was added at the sowing time.On 20 and 24 November 2003 seeds of wheat variety Acsad were planted at Bakrajow and Kalar respectively.The plants from Kalar location were harvested on 26 may 2004 while at Bakrajow the harvesting was conducted on 1 June 2004.Soil samples were taken from all experimental units at (0 to 30 cm) depth before sowing and after harvesting, then air dried thoroughly mixed, ground passed through a 2 mm sieve, and stored in plastic bottles prior to analysis.Some physical and chemical properties of the soils are given in (table 1).Electrical conductivity (EC) was measured for the soil saturation extract using EC-meter, model (WTW 82362 Weilheim, Germany).pH was measured in a saturated peaste using a pH-meter, model (Microprocessor pH meter, Hanna pH 211).Organic matter was determined by dichromate oxidation (Walkley and Black method) as described in Jackson (1973).The total calcium carbonate equivalent CaCO 3 was determined by a rapid titration method (Rayment and Higginson, 1992).Cation Exchange Capacity (CEC) was (ISSN 1815 -316 X) Vol.(39) No.
(2) 2011 determined by saturation with 1M NH 4 OAc at pH 8.1.Soluble HCO 3 -, Cl -and Ca 2+ + Mg 2+ were determined using titration methods (Page et al., 1982).Na + and K + were determined by using (Flame Photometer).SO 4 2-was indirectly determined from combined Ca and Mg by titration with (0.02M) EDTA disodium salt according to Jackson (1958).Available P was determined by extracting the samples with 0.5M NaHCO 3 (Olsen et al., 1954).The particle size was determined according to international pipette method as described by Day (1965).

RESULTS AND DISCUSSION
Influence of different levels of Mg and P fertilizer and their interaction on grain weight: Table (2) shows the significant effect of Mg, P and their interaction on grain yield at Bakrajow location, the highest values 5142.6,5113.3 and 5605.2 kg ha -1 were recorded from treatments, Mg 1 , P 1 and Mg 2 P 3 respectively.The above results indicated that the combination between Mg and P caused the decrease in P-fertilizer requirement for the highest yield.Table (3) indicated that the Mg, P-fertilizer and their interaction were no affected significantly on grain yield this may be due to the high concentration of Mg in Kalar soil (4.20 mmol c kg -1 ) and high 1.2 ratio of Na/Ca ratio this may causes the increase in phosphorus availability the similar results were obtained by Esmail (1992).Influence of different rates of Mg, P fertilizer and their interaction on P concentration and P uptake of wheat grain at Bakrajow location (kg ha -1 ): Table (4 and 5) indicated to significant effect of Mg, P rates and their interaction on phosphorus concentration and uptake at level of significant 0.05.(ISSN 1815 -316 X) Vol.(39) No.
(2) 2011The highest values of phosphorus concentration (4.65, 4.18 and 5.00 mg g -1 ) were recorded from Mg 3 , P1 and Mg 3 P 3 respectively, but the highest wheat yield were not recorded from the above treatments as mentioned before (table 2) since the concentration of nutrients are not responsible for limiting the yield but the nutrient balance index is responsible for limiting the yield or increasing in nutrient balance in plant causes increase in yield as mentioned by Darwesh (2007).He indicated to the highest wheat yield in treatment or treatment combination which has the highest nutrient balance (low nutrient balance index NBI).On the other hand the highest P uptakes (2256.43, 2164.78 and 2717.20 kg ha -1 ) were recorded from Mg 3, P 1 , and Mg 1 P 1 treatments, this means the increase in P uptake to a certain level caused increase in wheat yield due to the role of phosphorus in seed formation and increase in weight of 1000 seeds (Salih,2008).Influence of different rates of Mg, P fertilizer and their interaction on P concentration and P uptake of wheat grain at Kalar location (kg ha - 1 ):Table (6 and 7) shows the increase in rates of Mg and P to a certain level caused a significant increase in phosphorus content of grains at level of significant 0.05, the highest values (4.50, 4.20 and 4.80 mg g -1 ) were recorded from the treatments Mg 3 , P 2 and Mg 3 P 3, but the highest yield were not recorded from the mentioned treatments this may be due to role of nutrient balance in limiting wheat yield instate of nutrient concentration and uptake.On the other hand the highest P uptakes (1199.38,1241.05 and 1480.52 kg ha -1 ) were obtained from treatments Mg 3, P 2 and Mg 0 P 2 respectively.It is clear that the yield of wheat at Bakrajow location is twice to its yield at Kalar location this may be due to the following reasons: 1-The amount of rainfall was 320 and 570 mm year -1 at Kalar and Bakrajow respectively.2-The chemical composition and EC of the soil solutions were differ (table 1).The similar results were recorded by Esmail and Darwesh (2007).
3-The soil organic matter content and CEC of Bakrajow soil were higher than their values in Kalar soil while the calcium carbonate content of the Bakrajow soil was lower than its content in Kalar soil(table,1).Which caused the increase in wheat yield at Bakrajow location in comparing with Kalar location .These results agree with those recorded by Salih (2008).He indicated to the influence of soil chemical and physical properties on wheat yield.

Table ( 1
): some physical and chemical properties of soil used in field experiments.

Table ( 2
): Influence of different rates of Mg, P and their interaction on wheat grain yield (kg ha -1 ) at Bakrajow location.

Table ( 6
):Influence of different rates of Mg, P and their interaction on phosphorus concentration (mg g -1 ) at Kalar location.