Effect of Different Sources and Amounts of Nitrogen on Root Yield and Some Qualitative Characteristics of Sugar Beet

Nitrogen management (N) is one of the important factors in improving root yield and quality of sugar beet (Beta Vulgaris, L). Suitable source and rate of N fertilizer application are crucial to produce a high–yielding, high-quality sugar beet crop. The aim of this study was to evaluate the response of sugar beet to three levels of nitrogen fertilizer including N application based on soil test (125 kg ha-1), 25% less and 25% more than that one and four N sources including Urea (U), ammonium-nitrate (AN) and two delayed-release N sources e.g. Urea soaked with sulfur (domestic production) and sulfur coated urea (SCU). A field experiment was carried out during 2006/2007 and 2007/2008 growing seasons at the Agricultural Experimental Station of Miandoab in West Azerbaijan, Iran. Plots were arranged in a factorial randomized complete block design with three replications. The results revealed that, N rates influenced significantly root and sugar yields and the superiority was to adding 125 kg ha-1 pertinent to soil-based-test rate treatment. N rates did not influence sugar beet response to N sources. The value of mentioned parameters was not affected by N sources. N sources had consistent effects on mineral N (N-NO3 and N-NH4) concentration in the soil. Mineral N content increased with increasing N rates. The highest amount of mineral N contents were measured in N rate applied based on soil test in the form of AN source. The obtained results are recommended by application of N entirely in pre-plant in the form of delayed-release sources or split application in the form of, Urea or AN.