17 A. Ali A. Ahmad T. Khaliq J. Akhtar Journal of Animal and Plant Sciences JAPS 20122012/08/01 22 4 1070-1075 1018-7081 NA <p>Planting densities and nitrogen application rates are the major production factors contributing to the final yield of crops especially for sunflower being a non branched plant. Experiments were conducted to assess the effects of planting densities &amp; nitrogen rates and their interaction on growth and yield of two sunflower hybrids during spring season, 2010 and 2011. In treatments, there were two hybrids (Hysun-33 and S-278), two planting densities, 8.33 and 5.55 plants m-2 (20 and 30 cm plant spacing) with three levels of nitrogen (100, 125 and 150 kg N ha-1). The Split split plot design was used for layout of trial. The results showed significant difference for both of the hybrids in all the studied parameters except, number of plants m-2 in both years of experiments. In comparison of hybrids, S-278 was highest for yield and yield components while less in plant height. Averaged overall of both the years of trial, Maximum achene&rsquo;s yield (3.39 t ha-1, 2.80 t ha-1) was recorded for S-278 and Hysun-33 hybrid, respectively. Increasing plant density increased the final achene, s yield whereas, head diameter, 1000- achene&rsquo;s weight and seed yield per plant decreased. The Nitrogen application markedly enhanced growth and yield by affecting plant height, head diameter and thousand achene&rsquo;s weight. The interaction between hybrids x planting densities, and hybrids x nitrogen was significant for plant height, head diameter and achene&rsquo;s yield ha-1 but non- significant for 1000- achene&rsquo;s weight and plant population m-2. Among hybrids the overall yield response of S-278 was highest at plant spacing 20 cm (8.33 plants m-2), with125 kg ha-1 nitrogen application levels in both years.</p> achene, growth, nitrogen, planting densities, yield. Pakistan Agricultural Scientists Forum https://thejaps.org.pk/AbstractView.aspx?mid=2012-JAPS-442