Abstract:

In this experiment，we used one-year-old apple rootstock（Malus hupehensis Rehd.）as
materials and 15N labeled tracer technique as tool，to investigate the effect of using each nitrogen forms in
different time by the index of N utilization and loss. The results showed that in the treatment of 17 May，
the biomass of plant，which was treated with inorganic nitrogen（NH4
+-N and NO3
--N），was obviously
higher than the others. Under the treatment of ammonium nitrogen and nitrate nitrogen，the 15N utilization
rate of plant reached its maximum 13.68% and 13.25%，which were significantly higher than the 5.25% of
organic nitrogen. The loss of nitrification and ammonia volatilization was also stay low，such as the loss of
NO3
--N through ammonia volatilization，was only account for 1.83% of the nitrogen applied. Under the
treatment of 15 July，the utilization ratio of inorganic nitrogen decreased significantly，but it had hardly effect on the index of utilization ratio and ammonia volatilization loss under the treatment of organic
nitrogen. Therefore，using NH4
+-N and NO3
--N in 17 May is an effective measure to ensure the growth of
plant and high level of nitrogen utilization，and when they are applied in 15 July，reasonable collocation of
organic nitrogen can reduce the loss of nitrogen efficiently.

Key words: nitrogen forms, soil, N absorption, N loss