Study On Differences In Nitrogen Use Efficiency Among Sugar Beet Cultivars And Their Physiological Basis

In this experiment,the high-sugar sugar beet variety（KWS1197）,high-yield sugar beet variety（HI1003）and standard sugar beet varieties（IM1162,SX1511）were used as the test materials,and the field test was adopted under different nitrogen application treatments(N₀,0 kg/hm²N;N₇₅,75 kg/hm²N;N₂₂₅,225 kg/hm²N),measured the dry matter,root shoot ratio,nitrogen accumulation and distribution,nitrogen use efficiency and yield quality of sugar beet varieties at each growth period,analyze the relationship between nitrogen use efficiency differences between varieties and sugar beet yield quality,and explored the physiological basis of nitrogen use efficiency characteristics and differences of different varieties,in order to provide a theoretical basis for rational application of nitrogen fertilizer and nitrogen-efficient sugar beet varieties.The main results are as follows:1.The characteristics of nitrogen uptake and utilization during the growth period of sugar beet showed a unimodal curve,which reached its peak on the early stage of root-tuber growth and sucrose accumulation,the shoot of dry matter allocation of high-yield and high-sugar varieties increased by 4.57%～36.77%compared with the standard varieties under the N₀and N₇₅treatment,and the root shoot ratio of standard varieties was higher than that of high-sugar and high-yield varieties.Under N₂₂₅treatment,the shoot and root nitrogen accumulation of high-yield and high-sugar cultivars was higher than that of standard varieties on harvest period,and the shoot of nitrogen accumulation of high-sugar variety was significantly higher than that of other varieties.2.The leaf area index and nitrirate reductase activity of sugar beet cultivars peaked on root-tuber growth and sucrose accumulation stage,under the treatment of N₀and N₇₅,the leaf nitrate reductase activity,root of sucrose content of standard and high-sugar varieties were higher than high-yield variety,and the nitrate reductase activity was the highest in high-sugar varieties;Under N₂₂₅treatment,the SPAD value and shoot of soluble protein content of high-sugar and high-yield cultivars were significantly higher than those of standard varieties,and the SPAD of high-sugar variety was the highest.3.Under the treatment of N₀and N₇₅during the harvest period,the yield,sugar content and nitrogen utilization efficiency（NUt E）of high-sugar and standard sugar beet varieties were higher than high-yield variety.The nitrogen fertilizer utilization efficiency（NUE）during harvest was the highest in the high-sugar variety,which increased by 58.44%and 71.26%compared with the standard varieties SX1511 and IM1162,respectively.Under N₂₂₅treatment,the high-yield and high-sugar varieties increased by 5.15%～14.06%compared with standard varieties.4.The nitrogen uptake and utilization of sugar beet varieties showed the characteristics of low at seedling stage,highest at foliage rapid growth stage and root-tuber growth and sucrose accumulation,and reduced sugar accumulation period,but the nitrogen uptake and utilization of different types of varieties varied significantly at root-tuber growth and sucrose accumulation stage,showing obvious variety characteristics.Under low nitrogen treatment,NUE was positively correlated with yield and sugar yield during root-tuber growth and sucrose accumulation stage,and NUt E was positively correlated with sugar content during harvest period.Under high nitrogen treatment,NUE was positively correlated with yield and sugar yield during root-tuber growth and sucrose accumulation stage,and nitrogen uptake efficiency（NUp E）was negatively correlated with sugar content at harvest stage.In summary,high-sugar and standard varieties had higher nitrogen utilization efficiency under low nitrogen conditions,and their physiological basis was higher leaf nitrate reductase activity,shoot and root sucrose content.Under the condition of high nitrogen,the yield varieties had a higher nitrogen fertilizer utilization efficiency,and their physiological basis was higher leaf area index,SPAD and shoot of soluble protein content.The root-tuber growth and sucrose accumulation stage is the key period for nitrogen to regulate the quality of sugar beet production.