2006 Volume 52 Issue 2 Pages 101-105
Ammonium nitrogen or nitrate nitrogen fertilizer was applied to alfalfa seedlings at nitrogen concentrations of 10, 20, 30 and 40ppm to investigate the effects of the chemical form and concentration of nitrogen fertilizer on root system development. The plant dry weight, taproot length and total root length in the ammonium group were significantly greater than the corresponding values in the nitrate group, at nitrogen concentrations up to 20ppm. There were no differences in these characters between the two groups at nitrogen concentrations of 30 and 40ppm. In contrast, the specific root lengths of the taproot and lateral roots were higher in the ammonium group than in the nitrate group at concentrations up to 20ppm, but the reverse took place at concentrations of 30 and 40ppm. These findings indicate that the higher growth-promoting effect of ammonium nitrogen as compared with nitrate nitrogen is lost at nitrogen concentrations exceeding 30ppm, and that development of root branches is promoted by high concentrations of nitrate.
