Impact of Different Sources of Nitrogen And Water Stress on Onion Plant (Allium cepa L.) Using N-15.

Two field experiments were carried out during the two growing seasons of 2013/2014 and 2014/2015 at the experiential farm at the Nuclear Research Center, Atomic Energy Authority, Inshas, Egypt. These experiments were intended to evaluate the impact of three irrigation intervals, 4, 8 and 16 days under mineral (ammonium nitrate) and organic (Japanese quail manure) nitrogen sources at rates 60, 40, and 26 kg N/faddan on growth and yield of onion plant, in sandy loam soil. The results revealed that irrigation treatments under mineral nitrogen had a significant effect on chlorophyll content, total and bulb dry weights at harvest and also on the biological yield (kg/m(2)). However, total and bulb dry weight and economical yield did not reflect significant differences under different irrigation treatments and nitrogen application at harvest. Total and bulb dry weights at harvest were increased by increasing mineral nitrogen rates and there are no significant differences on chlorophyll content, biological and economical yield. On the contrary, organic nitrogen rates significantly affected the economical yield. The highest mineral nitrogen utilized percentage values were 27.33% for application 26 kg N/faddan compared to the higher and mediate one (19.45 and 12.59%) respectively, while, the highest water use efficiency values were at irrigation by the lowest water treatment (0.28 m(3)/0.6m(2)) for a biological yield as well as economical yield for the same treatment.