الفهرس 
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Abstract
Two field experiments were conducted in a private farm at El-Salhiea City; Sharkia Governorate during two summer seasons of 2007 and 2008 to investigate the effect of different rates and doses of nitrogen, phosphorus and potassium on corn plant (Zea mays L.). 90 treatments were arranged in a factorial randomized complete block design with three replicates; which were the simple possible combination between five treatments of N-fertilization with 2 different applications (2 and 4 doses), three levels of P-addition and three rates of K-applied. The following treatments were used:
1 Nitrogen fertilization treatment: five levels of 30, 60, 90, 120 and 150 kg N/fed.
2 Phosphorus fertilization treatment: three levels 20, 40 and 60 Kg P2O5/fed. Potassium fertilization treatment: three levels of 10, 20 and 30 Kg K2O/fed.
All treatments were investigated twice: once with an addition of N-fertilizer in four doses and the other with an application of nitrogen in two doses. Thus, the total numbers of treatments were 90 treatments. These treatments were conducted in 270 plots.
Ammonium nitrate (33.5%N), super phosphate (15.5% P2O5) and potassium sulphate (48%K2O) were the respective of N, P and K sources. Every level of N-fertilizer was divided into four doses 40, 20, 20 and 20% which was applied after2, 4, 6 and 8 weeks after sowing. On the other hand, for the application of nitrogen level in two doses all levels of N were divided into two equal doses which were applied after 2 and 6 weeks after sowing. Level of P and K fertilizers were added in two equal doses after 2 and 6 weeks from sowing for all treatments.
The obtained results of this investigation can be summarized in:-
1. Chlorophyll content:
• The effect of nitrogen fertilization doses on chlorophyll was positive and significant in both seasons. The maximum value of chlorophyll was accompanied with 4 doses. Chlorophyll content increased significant with increasing nitrogen application levels in both seasons. The highest value was obtained at the rate of 120 kg N fed-1 during 1st and 2nd seasons. With regard to the effect of interaction between N fertilization (rates and doses), phosphorus and potassium levels on chlorophyll content it can be observed that the highest values of chlorophyll was obtained by applying N fertilization in 4 doses at rate 120 kg N fed-1 + 40 kg P2O5 fed-1 + 10 kg K2O fed-1 in both seasons.
2. Fresh weight and dry weight of flag leaves (g):
• Regarding the effect of nitrogen fertilization doses, significant effect on F.W and D.W of flag leaves (g) in both seasons and noticed that N fertilization treatment applied in 4 doses gave the highest values of F.W and D.W flag leaves in both seasons. As for the interaction effect between the previously mentioned treatments the highest values of flag leaves F.W and D.W were obtained with N added fertilization in 4 doses at rates 120 kg N fed-1 + 40 kg P fed-1 + 10 kg K fed-1 in both season .
3. N, P and K in ear leaf 75 (DAS) (%):
• The statistical analyses reveal that the amounts of N, P & K concentration were higher with N fertilization applied 4 doses than 2 doses in two seasons, and this effect was significant. The effect of K fertilizer levels on N, P & K concentration % in leaves 75 DAS was significant. K fertilizer level at 10 kg K2O fed-1 gave the highest values to N, P & K concentration in leaves 75 DAS, respectively. There was high significant effect on N, P concentration in ear-leaf, 75 DAS in both seasons resulted from the interaction among nitrogen fertilization doses, phosphorus and potassium levels and there had No significant effect with K concentration in leaves, 75 DAS during both seasons.
4. 100-grain weight (g):
• With respect of N-doses, 100-grain weight increased with N fertilization added in 4 doses treatment than 2 doses, and this increase was significant in both seasons. The interaction effect recorded that the highest value of 100-grain weight was obtained with N fertilization in 4 doses at the rates of 120 kg N fed-1 + 40 kg P2O5 fed-1 + 10 kg K2O fed-1.
5. Grain and stalks yield (ton fed-1):
• Applying N fertilization levels in 4 doses gave the highest values of grain and straw yield in both seasons as compared with 2 doses. It is obvious that, the highest values of straw and grain yield were obtained by splitting N fertilization into 4 doses at the rates of 120 kg N fed-1 + 40 kg P2O5 fed-1 + 10 kg K2O fed-1 in both seasons.
6. N, P and K concentration in grain (%):
• Impact of N fertilization doses on N, P & K concentration in grain in both seasons. The statistical analyses reveal that the amounts of N concentration were higher with N fertilization divided into 4 doses than 2 doses in both seasons, and this effect was significant.There was a high significant effect on N concentration in grain in both seasons resulted from the interaction among nitrogen fertilization rates & doses, phosphorus and potassium levels. There wasn’t any significant effect on P and K concentration resulted from the interaction effect.
Recommendation:
Under the same conditions of this investigation, it could be recommended that the most suitable treatment for cultivation of corn in salheia soils representative in adding of N-fertilizer in four doses at the rate of 120 kg N.fed-1 in combination with P and K fertilizers at the rates of 40 and 10 kg.fed-1, respectively. This can be producing the highest yield of corn plant.