Effects of potassium on sugar, vitamin C, nitrate contents and their relevant enzymes of cucumber in solar-greenhouse

In order to explore the affecting mechanism of potassium on cucumber quality and provide a scientific and (rational) fertilizer practice for cucumber planting, the effect of potassium fertilization on main quality and their correlative enzymes of cucumber in solar-greenhouse were studied. The test crop was Jinyou No.1 and 5 application rates of K (K2O 0, 300, 600, 900, and 1200 kg/ha) were set up in this experiment. The result indicated that both the soluble sugar content and SPS activity of fruit and leaves of cucumber increased when application rate of K2O was in 300900 kg/ha scope. However, when 1200 kg/ha K2O was applied,both of them showed a drop tendency. There was a positive correlation between the soluble sugar content of fruits and SPS activity of leaves and fruits, but no obvious correlation between sugar content and SPS activity of leaves was found. When 300900 kg/ha K2O were applied, Vc content of fruits were higher than that of CK. The APX activity decreased in leaves while increased in fruits. Both in leaves and fruits, the (nitrate) content decreased with the increase of K2O. The NR activity of leaves were relatively higher, and increased with the increase of K2O application when the application rate of K2O was in the scope of 0900 kg/ha, however, it (decreased) markedly when 1200 kg/ha K2O was applied. The NR activity of fruits was quite low, and there were not obvious differentia among different treatments.