Four experiments for cucumber (cv. Deltastar) crops were carried
out in greenhouses located at Shanghai (32◦N, 121◦E) during
2005 and 2007. In each experiment, cucumber seedlings with the
same size were planted in pots with substrates and irrigated by
drip fertigation. Plants were pruned to a single stem and one flower
(fruit) was kept at each node from the 6th node onwards, and only
one fruit was kept per fruit cluster. Standard commercial crop management
practices (except nitrogen concentration of the nutrient
solution during nitrogen treatment period) were used for growing
cucumber crops.
Different levels of nitrogen treatments and type of substrates
were used in order to create different levels of plant nitrogen status.
Detailed information about the experimental periods, type of
substrates and greenhouses, planting density and levels of nitrogen
treatments is given in Table 1. There were 17 treatments in total
in the four experimental studies (Table 1). To investigate the saturated
nitrogen concentration (of the nutrient solution) for normal
crop growth, 5 levels of nitrogen treatments were used in Exp 1
(Table 1). According to the result of Exp 1, the saturated nitrogen
concentration was determined as 160 mg N L−1. In the following
two experiments (Exps 2 and 3), 4 levels of nitrogen treatments
were used (Table 1). In Exp 4, since pure perlite was used as substrate
in which no nitrogen is available, a level of 120 mg N L−1 (the
standard level of nitrogen concentration of nutrient solution used in
commercial greenhouse cucumber production in China) was added.
Nitrogen treatment at level of 17.5 mg N L−1 in Exp 4 was removed
because it is too low to allow the plants grow long enough for
experimental measurements. All nitrogen treatments, started at
flowering development stage, were conducted through supplying
nutrient solution with different levels of nitrogen concentration.
Detailed information about the nutrient solution is presented in
Table 2