can be lower than 10% (Zhu et al., 2005). Consequently, large
amount of unused nitrogen has been released to the environment
and has led to adverse environmental impacts (Gollany et al., 2004;
Beman et al., 2005), as well as accumulated compounds harmful to
humans in vegetables (Ruiz and Romero, 1999). Therefore, it is very
important to optimize greenhouse crop nitrogen management to
reduce environmental hazards while keeping yield level. For the
optimization of nitrogen management for crop productions, it is
essential to quantify the effects of nitrogen on crop growth process
and yield.