Light-response characteristics of photosynthesis of drip-irrigated sugar beet under different nitrogen fertilizer managements

Effects of two split application ratios of nitrogen fertilizer (R1: half of the total nitrogen fertilizer was applied on 13 June, and the rest was applied on 1 July; R2: two equal amounts of N fertilizer accounting for 70% of total were applied on 15 June and 1 July, respectively, and the rest was applied on 1 August) and three N fertilizer application rates (75, 150, and 225 kg ha-1) on chlorophyll content, photosynthetic characteristics, and root yield of sugar beets were studied. The results showed that with N fertilizer application rates of 150 and 225 kg ha-1, R2 treatment significantly decreased light-compensation point, but increased light-saturation point and actual photochemical efficiency at the storage root development compared to R1 treatment. The R2 treatment with the N fertilizer application rate of 150 kg ha-1 significantly increased sugar yield by 5-29% compared to other treatments.