The effect of partial replacement of nitrate with arginine, histidine, and a mixture of amino acids extracted from blood powder on yield and nitrate accumulation in onion bulb

The effect of replacement of 20% nitrate-N in the nutrient solution by arginine, histidine, and blood powder amino acids on nitrate metabolism and bulb yield of two onion cultivars (Allium cepa L., cvs. Dorrcheh and Valenciana) was investigated. Addition of amino acids into the nutrient solution significantly reduced nitrate accumulation in onion bulb. This decrease was accompanied with lower activity of nitrate reductase (NR) and higher production of ammonium and amino acid in onion bulb. A mixture of amino acids extracted from blood powder was more effective than individual arginine and histidine treatments in decreasing bulb nitrate concentration. Onion plants supplied with amino acids accumulated higher levels of total nitrogen and amino acids in their bulbs compared with those unsupplied with amino acids. Activity of glutamine synthetase (GS) in onion bulb was also increased by amino acids. Application of amino acids significantly enhanced fresh and dry matter yield of onion bulb, although this increase was smaller by histidine in comparison with blood powder amino acid and arginine treatments. According to the results obtained, the mixture of amino acids extracted from blood powder can be used as a source of nitrogen in nutrient solution culture of onion.