In the aim of studding the effect of date and levels of nitrogen fertilization on the seeds yield of summer squash (cv. Mulla Ahmed) ,an experiment was conducted at Vegetable field/ College of Agriculture and Forestry/ Mosul University, during 2007 and 2008 spring growing season.
Results revealed that application of nitrogen fertilizer at fruit set stage gave the highest and significant increase in seed length and diameter ,seeds weight fruit-1 and the total yield of seeds during both seasons ,whereas ,the increase was significant only in weight of 1000 seeds in 2007 season ,and in seed germination in 2008 season, on the other hand , there were non-significant increase in both seasons for number of fruits held for seeds extraction and purity percentage . It was also found that nitrogen fertilization at a level of 320 kg.N.ha-1 was distinguished significantly in fruit weight ,weight of 1000 seeds, seeds weight fruit-1 , seed yield plant-1 and the total yield of seeds during both seasons , but the three levels of nitrogen(80 ,160, 320 N.ha-1 fertilizer did not differ significantly with each other in the growing season of 2007 in number of fruits ,seed diameter and purity %, and in purity % and germination % during 2008 season .The best interaction treatment produced a highest total yield of seeds (2106.8 , 2668.4 kg. ha-1 ) in both seasons respectively , occurred between application of nitrogen fertilizer at flowering stage of 50% plants + 320 kg.N. ha-1 .The total yield of seeds was highly and significant correlated with number of fruits held for seeds , seeds weight fruit-1 ,weight of 1000 seeds ,seed length and diameter in both growing seasons .