Effects of water and nitrogen interaction on photosynthetic characteristics and yield of cucumber in greenhouse

Potosynthetic rate, transpiration rate and water use efficiency at different growth stages and yield of cucumber under different water and nitrogen levels were studied in solar greenhouse to investigate the effects of water and nitrogen interaction on cucumber photosynthetic characteristics and production. The relationship between photosynthetic rate and cucumber yield were analyzed too. The results show that photosynthetic rate and transpiration rate reach the highest in full fruit stage, while water use efficiency in primary fruit stages. Under conventional irrigation, photosynthetic rate and transpiration rate increase with increasing nitrogen rate, and reach the highest under 7 470 m³·hm^-2 irrigation quantity and 1 200 kg·hm^-2 nitrogen rate (W₁N₁₂₀₀), but are not significantly different from those under W₂N₆₀₀ (irrigation quantity 5 190 m³·hm^-2, nitrogen rate 600 kg·hm^-2). Water use efficiency reaches the highest under W₂N₆₀₀, which is 1.08 and 1.24 times of those under W₁N₁₂₀₀ and CK respectively. Water and nitrogen interaction significantly affect cucumber yield and yield components. The optimal treatment is W₂N₆₀₀ with 30% reduction in water and 50% reduction in nitrogen compared with conventional treatment. It yields the highest, 17.06×104 kg·hm^-2. Photosynthetic rate presents a conic relationship with yield, fruit number per plant and average fruit weight respectively, in which the best fitting equation is at the full fruit stage.