| Sugar beet is an important raw material for sugar,and also an important economic crop in the arid and cold regions of China.However,drought and water shortage in such areas is one of the main factors limiting the increase in sugar beet yield.Over the years,in order to achieve high yield,farmers have severely exceeded the standard for nitrogen fertilizer application,resulting in a continuous decline in sugar content.How to maximize the fertilizer utilization efficiency of water and nitrogen is an urgent problem to be solved in the sustainable development of sugar beet production.The drip irrigation under plastic mulching technology is a widely used water-saving irrigation method.It can increase the yield and quality of crops by saving water,increasing temperature,squeezing grass and increasing fertilizer utilization ratio.Therefore,this cultivation pattern was used in the experiment to study the effect of water and nitrogen coupling on physiological performance,yield and quality of sugar beet in Liangcheng County,Inner Mongolia for two consecutive years from 2016 to 2017,so as to reveal the physiological effects of water and nitrogen coupling on sugar beet growth and provide scientific basis for the management of water and fertilizer with high yield and quality of sugar beet.The research results were as follows:1.With drip irrigation under plastic mulch,the yield increased first and then decreased with the increase of irrigation volume at the same nitrogen level.At the same irrigation level,the yield did not change with the increase of nitrogen amount below 225 kg/hm2,and then decreased.The results of the two-year experiment showed that the root yield and sugar yield reached the maximum when the irrigation amount was 13501427 m3/hm2and the amount of nitrogen application was 150179.22 kg/hm2.2.With drip irrigation under plastic mulch,in the root and sugar growth period,the leaf area index,the net photosynthetic rate and the dry matter accumulation all increased with the increase of irrigation volume at the same nitrogen level;at the same irrigation level,the above three photosynthetic indexes did not show the same change rule with the change of nitrogen applecation.During the sugar accumulation period,the root-shoot ratio was decreased with the increase of irrigation and nitrogen amount.The light use efficiency was higher when irrigated three times and the amount of nitrogen fertilizer was 150179.22 kg/hm2.Leaf area index and Net photosynthetic rate during the root and sugar growth period can be used as physiological indexes for high-yield sugar beet.3.With drip irrigation under plastic mulch,leaf water potential of sugar beet was controlled between-0.38-0.23 MPa in leaf fast growth stage and root and sugar growth period,and was-0.45-0.38 MPa in the sugar accumulation period,the sugar beet could obtain high yield both in root weight and sugar content.There was no significant difference in plant water content among different treatments.The stomatal conductance and transpiration rate of sugar beet leaves were affected little by nitrogen application,and increased with the increase of irrigation amount.The water consumption of sugar beet increased but the irrigation water use efficiency decreased with the increase of irrigation amount.Leaf water potential can be used as physiological indexes for irrigation in leaf fast growth stage and root and sugar growth period.4.With drip irrigation under plastic mulch,the activity of nitrate reductase?NR?,glutamine synthase?GS?in the leaves and nitrogen,phosphorus and potassium absorption all increased with the increase of irrigation and nitrogen amount,and the former two metrics were maximum in leaf fast growth stage.The activity of GS in root was maximum in the period of root and sugar growth.With the increase of nitrogen amount,nitrogen fertilizer absorption and utilization rate,nitrogen partial productivity,the physiological utilization and agronomic utilization of nitrogen fertilizer were all decreased.5.A regression model was established for the coupling of water and nitrogen and yield and quality in sugar beet with drip irrigation under plastic mulch.The regression model for the yield and the nitrogen application amount and the irrigation volume was:Y=-0.127N*N+44.355N–0.004 N*W+10.797W–0.004 W*W.According to the simulated optimization method,the optimal irrigation volume and nitrogen supply amount were1193.591227.5 m3/hm2 and 162.09167.58 kg/hm2 respectively.The regression model for sugar content and nitrogen supply amount and irrigation volume was:Y=17.17–7.48*10-6N*N+1.91*10-3N–1.65*10-6 N*W–1.19*10-3W–4.1*10-7 W*W.The optimum irrigation volume and nitrogen application amount were 535.33555.08 m3/hm2 and133.07145.06 kg/hm2 respectively.The regression model for the sugar yield and the amount of water and nitrogen was:Y=-0.027N*N+10.058N–0.002 N*W+1.336W–0.0005 W*W.The suitable amount of irrigation water and nitrogen application were1045.691084.11 m3/hm2 and 153.12158.21 kg/hm2 respectively. |
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