Effects Of Water And Nitrogen Coupling On Physiological Characteristics And Water-Nitrogen Use Efficiency Of Cucumber In Solar Greenhouse

For the problem of low water-nitrogen use efficiency in the protected cucumber production, we studied the effects of alternate fertigation on the growth, photosynthesis, yield, quality and water-nitrogen use efficiency of cucumbers.'Jinyou No.35'cucumber was chosen as the test cultivar. The experiment utilized the split-plot design with drip irrigation as main plots and nitrogen as subplots. The main plots was drip irrigation (conventional drip irrigation and alternate drip irrigation), the subplots was nitrogen (no nitrogen 0 kg/hm2; low nitrogen 450 kg/hm2; high nitrogen 900 kg/hm2). So there were six treatments in total. The chief results are showed as follows:1. The alternate fertigation decreased the plant height and stem diameter of cucumbers significantly, but the root growth characteristics and root activity were increased significantly. The alternate drip irrigation with low nitrogen improved the length and diameter of cucumber root, and increased root activity significantly.2. Compared to conventional drip irrigation, the alternate drip irrigation and nitrogen can improved the content of leaf pigment. The alternate drip irrigation reduced the leaf stomatal conductance, resulted in the reduction of leaf transpiration. There was no significant difference of net photosynthetic rate (Pn). Under the alternate drip irrigation with low nitrogen, Fv'/Fm1, OPS II, ETR were the highest, and the NPQ was the lowest. Through the analysis of JlP-test, AN1 enhanced performance of photosystem II, and electron transport.3. The alternate drip irrigation improved SS activity and increased the content of sucrose and reducing sugar. The conventional drip irrigation increased SPS activity and starch content. Nitrogen fertilizer improved SS and SPS activity, and increased the content of sucrose and reducing sugar. The content of starch decreased with increasing amount of nitrogen. The nitrogen metabolism enzymes in the alternate drip irrigation treatment were better than that of the conventional drip irrigation. The nitrogen fertilizer improved the content of total nitrogen and protein nitrogen. The SS and SPS activity, nitrogen metabolism enzymes activity were the highest under AN1, and the sucrose, reducing sugar, total nitrogen and protein nitrogen of stem and leaf were better than others.4. The water and nitrogen movement of the conventional drip irrigation soil migrated mainly vertically, but it migrated mainly laterally under alternate drip irrigation which reduced the leakage of water and nitrogen into deep soil. The alternate drip irrigation resulted in higher content of nitrate nitrogen than conventional drip irrigation from 0 to 40 cm soil layer. The content of nitrate nitrogen increased with increasing amount of nitrogen. AN1 significantly increased the activity of urease, phosphatase and hydrogen peroxidase enzymes of soil.5. For the quality of cucumbers, the content of nitrate and soluble protein under the same irrigation levels significantly increased with the increasing of nitrogen. However, the content of VC and soluble sugar increased at first and then decreased. Under the same nitrogen levels, the quality of cucumber fruit under the alternate drip irrigation was better than that of the conventional drip irrigation. The soluble sugar and VC content were higher than others under ANi, and the content of nitrate was lower. Principal component analysis showed that the quality of cucumber fruit was the best under AN1.6. Compared to conventional drip irrigation, the amount of irrigation water under the alternate drip irrigation decreased by almost 50%, but the average of water use efficiency increased by 79% in spring crop and 176% in autumn crop. There was no difference of yield between treatments or a little decline under alternate drip irrigation. The agronomy use efficiency of nitrogen (ANUE) declined with the increasing of nitrogen. Under the alternate drip irrigation, the low nitrogen was beneficial to achieve higher yield and ANUE. Under the conventional drip irrigation, high nitrogen (N2) increased the yield by only 0.9% than CNi, but the ANUE decreased by 37% in the spring crop.In conclusion, the alternate drip irrigation with low nitrogen can optimize coupling effect of water-nitrogen; improve water-nitrogen use efficiency significantly, which can be used as a water-nitrogen management mode for cucumber cultivation in solar greenhouse.