Abstract
The experiment was carried out in the private vegetable farm, Somail, Duhok government, during autumn growing season 2015, The aim was to studied the effect of humic acid on growth and yield of three cultivars of summer squash (Cucurbita pepo L.). The experiment was a split plot design within three replicate, in this study was used three concentration of humic acid (0, 25 and 59 mlg/ litter), and three cultivars of summer squash which were (Alexandria F1, Khatoon F1 and Ardendo 174 F1). The data was collected on: fresh and dry weight /plant, number of male, female flowers, sex ratio, length, diameter, weight of fruit, number of fruit /plant and total yield /hectars. The result showed that the consecration at 50mlg/liter of humic acid gave a significant increase in fresh, dry weight /plant, fruit length, number of fruit /plant and in total yield, the cultivar Ardendo 174 F1 gave a significant increase in most traits excepted the sex ratio and fruit diameter. and the interaction between the 50mlg/liter of humic acid and cultivar Ardendo 174 F1 gave a significant increase in fresh, dry weight /plant , female flower /plant , number of fruit /plant and total yield / hectar. The result indicated the a higher positive phenotypic correlation coefficient between the total yield /hectar , fruit weight with most traits .

Key words: humic acid , cultivar , correlation , squash , yield. *Part of M. Sci. Thesis of the second investigator .