effect of amino acid containing organic fertilizers on nitrogen use efficiency and qualitative and quantitative properties of sugar beet

in order to study the effect of organic fertilizers application on increasing nitrogen efficiency and also quantitative and qualitative characteristics of sugar beet, a series of experiments were performed for two years (2008 and 2009) using three amino acid containing organic fertilizers at motahari research station of sugar beet seed institute (sbsi), karaj, iran. four rates of organic fertilizers including control (no organic fertilizer), humiforte, humiforte + fosnutren, and humiforte + kadostim which were applied twice with 40 and 60 days interval after sowing and one per mil concentration, and four rates of n fertilizer including control (no n fertilizer), 30% less than optimum (100 kg/ha), optimum, and 30% higher than optimum level were evaluated in factorial experiment based on randomized complete block design with four replications. results showed that at 0-30 cm soil depth with 15 mg/kg n, 100 kg n level was the optimum level which resulted in 71 and 10.1 t/ha root and sugar yields, respectively. 70 kg/ha n level and humiforte + fosnutren organic fertilizer were placed in high sugar yield group (with 74.5 and 11 t/ha root and sugar yields, respectively). it was also shown that organic fertilizer application led to nitrogen efficiency improvement; however these compounds cannot be completely replaced by nitrogen fertilizer (with 60 and 9.16 t/ha root and sugar yields, respectively). since n fertilizer application may have deleterious effects on environment,  using appropriate organic fertilizers and consequently increased efficiency of nitrogen, may reduce n application.