MATERIALS AND METHODS

The field experiment was conducted at Tag AL-Ezz, Agricultural Research Station Farm, Dakahlia Governorate, Agricultural Research Center, Egypt, during 2005/2006 and 2006/2007 seasons to study the effect of foliar application with micronutrients and soil applied nitrogen levels on yield and its components, grain and seed quality of wheat cultivar Giza 168. In addition to, laboratory experiment was conducted at Seed Technology Research Unit at Mansoura, Dakahlia Governorate, Field Crops Research Institute, Agricultural Research Center, Egypt, to determine germination percentage, speed of germination and seedling vigor tests (seed quality) of seeds resultant from field trials.

Field experiment: A split -plot in CRB design with three replicates was used. The main plots were allocated to seven foliar nutrition treatments as follows: untreated control, spraying with water, spraying solution of: CuSO₄, Mn-EDTA, Fe-EDTA and Zn-EDTA at the rate of 500 ppm of each as well as the mixture of the micronutrients together at the rate of 500 ppm of each element. The foliar solution volume was 200 Liter fed^-1 and spraying was conducted by hand sprayer (for experimental plots) until saturation point twice after 30 and 50 days from sowing. The sub plots were assigned to three nitrogen level treatments of: 50, 70 and 90 kg N fed^-1. The nitrogen fertilizer in the form of ammonium nitrate (33.0% N) was used in two equal doses prior to each of the first and the second irrigations.

Before planting, soil samples for both physical and chemical analysis for the experimental soil were undertaken according to Jackson (1973) and corresponding data are presented in Table 1. Each experimental unit was 10.5 m² (3x3.5 m). The preceding summer crop was rice (Oryza sativa L.) in both seasons.

Potassium fertilizer in the form of potassium sulphate (48% K₂O) at the rate of 50 kg fed^-1 was applied in one dose before the first irrigation. Calcium super phosphate (15.5% P₂O₅) was applied during soil preparation at the rate of 150 kg fed^-1. The planting dates were at November 23rd and 26th in the first and second seasons, respectively. Wheat grains at the rate of 60 kg fed^-1 were broadcasted using (Afir) method. The other recommended agricultural practices for growing wheat were followed.

Studied characters
Yield components: At harvesting time, one square meter was randomly selected from each experimental plot to estimate the following characters: plant height (cm), number of spikes m^-2, spike length (cm), number of spikelets/spike, number of grains/spike and 1000 grain weight (g).

Table 1:	Physical and chemical soil characteristics at the experimental sites during 2005/2006 and 2006/2007

Yield determination: Grain yield (ardab fed^-1) was calculated by harvesting whole plants in each plot and left to dry on air, then they were threshed and the grains (which were at 13% moisture) were weighted (kg), then converted to ardab per fed (one ardab = 150 kg). Straw yield (t fed^-1): The straw resulted from each experimental plot was weighted in kg, then it was converted to tons per fed.

Wheat grain quality and chemical composition: Carbohydrates percentage in grains was determined by Hedge and Hofreiter (1962). Nitrogen in grains and straw was determined by microkjeldahl methods (Jackson, 1967). Crude protein percentage was calculated by multiplying the total nitrogen values in wheat flour by 5.17. Phosphorous in grains and straw was determined by the methods described by Cooper (1977). Potassium in grains and straw was determined using flamephotometer as described by Peterburgski (1968).

All data were statistically analyzed according to the technique of analysis of variance (ANOVA) for the split -plot design using MSTATC computer software package according to Gomez and Gomez (1984). Least Significant of Difference (LSD) method was used to test the differences between treatment means at 5% level of significance as described by Waller and Duncan (1969).

Laboratory experiment: The germination experiment consisted of four replications of 100 seeds from each treatment. 50 seeds were placed on two sheets of blotter paper in 14 cm diameter Petri-dishes. The blotter paper was moistened with adequate distilled water. The Petri-dishes were placed in a growth chamber at 20°C. Standard germination tests were followed according to AOSA (1993). Germination percentage was expressed as the percentage of seed germinating normally after 8 days. The four replications were also used to evaluate daily speed of germination (during germination test) according to Agrawal (1986). Shoot and root lengths (cm) were determined at random from 10 normal seedlings taken from each replicate at the end of standard germination test and dried in a forced air dry oven at 110°C for 17 h (Agrawal, 1986) to obtain seedlings dry weight in milligrams. Data were subjected to the statistical analysis according to the technique of Analysis of Variance (ANOVA) for the factorial completely randomized design as published by Gomez and Gomez (1984).

RESULTS AND DISCUSSION

Yield and yield components: Foliar application with the applied micronutrients had a significant effect on plant height, number of spikes m^-2, spike length, number of spikelets/spike, number of grains/spike, 1000-grain weight, grain and straw yields in both seasons (Table 2, 3). The mixture of four micronutrients (Cu, Mn, Fe and Zn) at the rate of 500 ppm of each significantly ranked first and produced the highest values of grain and straw yields as well as all its components with significant differences compared with the other singular micronutrient foliar application treatments in both seasons. Foliar application treatment with Zn was in the second rank and followed by Mn treatment. Cu and Fe treatments were seemed equally in their effect and the difference between them were insignificant in most cases. The lowest values of grain and straw yields and yield components were resulted from the untreated treatment in the two growing seasons. Such effects of foliar application with micronutrients (Cu, Mn, Fe and Zn) might be due to its critical role in crop growth, involving in photosynthesis processes, N-fixation, respiration and other biochemical and physiological activates and thus their importance in achieving higher yields. Similar results were reported by Welch et al. (1991), Hall and Williams (2003) and Kassab et al. (2004).

Data presented in Table 2 and 3 reveal that, grain yield and its components i.e., plant height, number of spikes m^-2, spike length, number of spikelets/spike, number of grains/spike, 1000 grain weight, grain and straw yield fed^-1 were significantly increased by increasing nitrogen fertilizer level up to 90 kg N fed^-1.

Table 2:	Plant height, No. of spikes m-2, spike length, number of spikelets/spike and number of grains/spike as affected by foliar application with micronutrients and nitrogen fertilizer levels during 2005/2006 and 2006/2007 seasons

Table 3:	1000-grain weight, grain and straw yields as well as crude protein and carbohydrates percentages in grains as affected by foliar application with micronutrients and nitrogen fertilizer levels during 2005/2006 and 2006/2007 seasons

These results were noticed in the two growing seasons. Wheat plants fertilized with the highest level of nitrogen (90 kg N fed^-1) had the highest values of grain yield and its components, followed by plants fertilized with 70 then 50 kg N fed^-1 in both seasons. Noteworthy, the percentage of increasing values of most mentioned characters due to increasing nitrogen levels from 50 to 70 kg N fed^-1 was more than those of increasing nitrogen levels from 70 to 90 kg N fed^-1. This means that the response of wheat to increase nitrogen levels from 70 to 90 kg N fed^-1 was less than that when nitrogen was increased from 50 to 70 kg N fed^-1. The most important role of nitrogen fertilizer in plant is mainly in its presences in the nucleic acid and protein structure. In addition, nitrogen is also found in chlorophyll molecule. Chlorophyll enables plant to transfer energy from sunlight by photosynthesis to assimilates (chemical energy form). Therefore, the nitrogen supply to the plant will influence the amount of protein, protoplasm and chlorophyll formed. In turn, this influences cell size and number, photosynthetic activity and growth, hence increasing all yield components as well as grain and straw yield per unit area. These results are in agreement with those obtained by David et al. (2005), Sieling et al. (2005) and Seadh and Badawi (2006).

Grain quality and chemical compositions: Quality parameters of grains (protein and carbohydrates percentages) and chemical composition i.e., N, P and K concentrations in grains and straw show significant response to micronutrients foliar application treatments in both seasons as shown in Table 3 and 4. Application with mixture of Cu, Mn, Fe and Zn at the rate of 500 ppm, resulted in the highest values of these traits with significant differences compared with other foliar application treatments in the two growing seasons.

Table 4:	N, P and K percentages in wheat grains and straw as affected by foliar application with micronutrients and nitrogen fertilizer levels during 2005/2006 and 2006/2007 seasons

Generally, it was observed that the foliar application treatments with micronutrients assorted as: Mixture>Zn > Mn>Fe>Cu>water> untreated in both seasons. This improvement in grains quality and chemical composition may be due to the role of microelements in maintaining balanced plant physiological growth. Even though micronutrients are present in small amounts in plants, they activate about 100 enzymes in plant. It is inferred that plant not to be able to survive without adequate of sufficient micronutrients because they are essential to the synthesis of DNA and RNA and to metabolizing carbohydrates, lipids and proteins. Micronutrients also play a key role in the release of carbon dioxide and in the function of vitamins (Marschner, 1995).

Data in Table 3 and 4 illustrate that crude protein and carbohydrates as well as N, P and K percentages in grains and straw were significantly increased by increasing nitrogen levels in both seasons, except K% in straw in both seasons. From the data, each increase in nitrogen associated with a significant increase in grain quality parameters, this observation was true in the two growing seasons. Generally, the highest values of these traits were obtained as a result of increasing nitrogen fertilization up to 90 kg N fed^-1. This improvement in quality parameter due to increasing nitrogen levels may be reflected to the role of nitrogen fertilizer in improving growth and dry matter accumulation which led to increasing the uptake of most nutrients. The results achieved in this work are partially compatible with those obtained by Allam (2005) and Mekhemar (2008).

Seed quality: Foliar application treatments with micronutrients exhibited significant effect on seed quality parameters (germination percentage, speed of germination, shoot length, root length and 10 seedlings dry weight) in both seasons (Table 5). The mixture of Zn, Fe, Mn and Cu at the rate of 500 ppm produced the highest values of the above mentioned characters in both seasons. Foliar application with Zn alone ranked after the formerly mentioned treatments in both seasons. Other foliar application treatment exceeded untreated (control) and spraying with water, this observation was true in both seasons. The improvement in seed quality parameters may be reflected to the role of microelements in enhance accumulation of assimilate in the grains (during grain filling stage) and thus the resultant seeds had greater individual mass and germinated quickly (Baskin and Baskin, 1998). Also, high micronutrient accumulation in seeds particularly Zn and Mn may be produce more viable and vigorous seedlings, because they supplying the young seedlings with these trace elements until it has developed a large root system enough to take over this role (Bouis et al., 2000). Similar results were reported by Roach and Wulff (1987) and Fenner (1992).

Seed quality characters were significantly affected due to increasing nitrogen fertilization rates from 50 up to 90 kg N fed^-1 in both seasons (Table 5). Each increase in nitrogen rates from 50 to 70 and 90 kg N fed^-1 associated with a significant increase in studied seed parameters in the two growing seasons. The highest values of seed quality parameters were resulted from those fertilized wheat plants with 90 kg N fed^-1. This enhancement in seed quality parameter due to increasing addition of nitrogen levels may be ascribed to increase N content of seeds which positively correlated with germination percentage and seedling size (Nylor, 1993).

Table 5:	Germination percentage, speed of germination, shoot length, root length and 10 seedlings dry weight as affected by foliar application with micronutrients and nitrogen fertilizer levels during 2005/2006 and 2006/2007 seasons

Table 6:	Number of spikes m-2, number of grains/spike, 1000 grain weight and grain yield as affected by the interaction between foliar application with micronutrients and nitrogen fertilizer levels during 2005/2006 and 2006/2007 seasons

Interaction: Regarding the interactions between foliar application with micronutrients and nitrogen levels on studied characters, there are many significant effects. We have reported enough the significant interaction on number of spikes m^-2, number of grains/spike, 1000 grain weight and grain yield only (Table 6). The best interaction treatment which produced the highest values of grain yield and its components was foliar application with the mixture of Cu, Mn, Fe and Zn (at the rate of 500 ppm) beside fertilization with 90 kg N fed^-1. Foliar spraying wheat plants with Cu or Mn or Fe or Zn or mixture plus adding 70 kg N fed^-1 exceeded treatment of untreated + 90 kg N fed^-1 in number of grains/spike, 1000 grain weight and grain yield in both seasons, except treatment of Cu + 70 kg N fed^-1 in 1000 grain weight in the second season only. Also, spraying wheat plants with Zn or mixture +70 kg N fed^-1 significantly surpassed treatment of untreated + 90 kg N fed^-1 in number of spikes m^-2 in both seasons. While, untreated +90 kg N fed^-1 treatment exceeded spraying wheat plants with Cu or Fe + 70 kg N fed^-1 (in both season) or Mn +70 kg N fed^-1 (in the second season) in number of spikes m^-2 without significant differences between them.

CONCLUSION

In general, the obtained results show that foliar application with mixture of studied micronutrients (Cu, Mn, Fe and Zn) at the rate of 500 ppm in addition to mineral fertilizing with the highest nitrogen level (90 kg N fed^-1) produced the highest values of wheat straw and grain yields as well as grain quality in addition to improve germination of the resultant seeds and seedling growth. Moreover, it can be recommended that spraying wheat plants with Cu or Mn or Fe or Zn or mixture (at the rate of 500 ppm) and adding 70 kg N fed^-1, which exceeded in grain yield upon untreated (control) + 90 kg N fed^-1.