This present study was carried out during 2003/2004 and 2004/2005 winter seasons in a private farm at Rafah, El-Areish, North Sinai Governorate, Egypt. This work aimed to study the effect of seeding rate (50 , 65 and 80 kg grains / fad.) and nitrogen fertilization level (40 , 60 and 80 kg N / fad) on grain yield, and yield attributes of Sids 1 wheat cultivar under rainfed conditions and newly cultivated sandy soil as well.
The number of spikes/m2 was not significantly affected by seeding rate in the first season, but however, was significantly increased due to the increase of seeding rate up to 65kg/fad. in the second season as confirmed by the combined analysis.
The grain weight/spike, number of grains/spike and 1000-grain weight were not significantly affected by varying the seeding rate in both seasons and their combined. However, the grain yield/fad, as well as the straw and total yields/fad. were significantly increased with each increase of seeding rate up to 80kg/fad. This was observed in harvest and crop indices when the seeding rate was increased from 40 to 80kg/fad.
Regarding N fertilization level, the grain yield/fad. and all its components were significantly increased with each N increment up to the addition of 80kg N/fad. The straw yield/fad failed to respond to the second N increment and hence the harvest index and crop index. The response equations of grain yield/fad. to the increase of N level were of the second order to where the increase of grain yield was diminishing in the two seasons, indicating that a predicted maximum N level of 72.6 kg N/fad. was quite enough to maximize the grain yield to 1022.9 kg/fad. in the first season whereas 84.0 kg/fad. were needed to maximize the grain yield to only 892.9kg/fad. in the second season.
The interaction between the two factors under study was without significant effect on grain, straw and biological yields/fad. The number of grains/spike and straw and biological yields/fad. were significantly affected by the interaction between seeding rate and N level. Under the three seeding rates, any increase in N level was accompanied by a significant increase in the averages of these characters but with different magnitudes.
Wheat grain yield/fad was positively and significantly correlated with most of the studied characters. Path analysis revealed that the main sources of grain yield variation according to their relative importance were number of spikes/m2, number of grains/spike and 1000-grain weight, where the direct and indirect effects of these traits contributed more than 86.89 % from the grain yield variation.