| In this study,the common buckwheat-Xinong 9976 was used as the material,and the two-year experiment was carried out in Yulin,Shaanxi Province from 2017 to 2018.Four nitrogen fertilizer treatments were set:N0,N1,N2,N3.The effects of different nitrogen application rates on the growth and development of buckwheat were studied by measuring the changes of SPAD values in the early flowering stage to the maturity stage of buckwheat,the dry matter accumulation of roots,stems,leaves and grains before seeding.The number of stem segments,the number of primary branches,the number of secondary branches,the number of clusters per plant,the weight of 1000 seeds,the number of grains per plant and the yield of plots were performed to explore the optimum nitrogen application rate of high yield of buckwheat in northern Shaanxi and the effect of nitrogen application on buckwheat agronomy traits.We measured the protein,fat,starch,flavonoid content and starch physicochemical properties of buckwheat grain to study the effect of different nitrogen fertilizer dosage on the grain quality of buckwheat.In addition,we determined the adenosine diphosphate glucose pyrolysis enzyme(ADPGPase)and granules in different stages of buckwheat grain combining the activities of starch synthase(GBSS),soluble starch synthase(SSS)and starch branching enzyme(Q enzyme)in order to study the effects of nitrogen on the activities of key enzymes in starch synthesis and the regulation of key enzymes on the structure of buckwheat starch,and synthesis rate.The main conclusions are as follows:Nitrogen application significantly increased the SPAD value of the main stem leaves of buckwheat,reached the highest at 180 kg/hm~2 nitrogen,and delayed the decrease of SPAD value in the late growth stage of buckwheat.The maximum accumulation of dry matter in various organs of buckwheat was significantly increased under various nitrogen treatments,and reached the maximum in 180 kg/hm~2 nitrogen or 270 kg/hm~2 nitrogen treatment.90kg/hm~2 nitrogen or 180 kg/hm~2 nitrogen treatment at the seedling stage and early flowering stage is more conducive to the accumulation of dry matter in various organs of buckwheat.The plant height,primary branch number,secondary branch number and single plant number of buckwheat increased first and then decreased with the increase of nitrogen application rate,reached the maximum at 180 kg/hm~2 nitrogen,and the number of nodes changed in two years.The nitrogen application was significantly greater than the control,but the difference between the nitrogen treatments was not significant.Nitrogen application significantly increased buckwheat yield.In 2017,production under N1,N2,and N3 buckwheat than that under the control increased by 27.78%,38.11%,and 40.00%,respectively.In 2018,the production under N1,N2,and N3 increased by 8.02%,22.15%and 10.60%compared with N0.The soil nitrogen compliance rate and nitrogen fertilizer physiological utilization rate decreased with the increase of nitrogen application rate;nitrogen fertilizer absorption and utilization rate and nitrogen fertilizer partial productivity decreased with the increase of nitrogen application rate in 2017,and were highest under 180 kg/hm~2 nitrogen treatment in2018.With the increase of nitrogen application rate,the crude protein content in buckwheat grains increased continuously,the flavonoid content increased first and then decreased,and the flavonoid content reached the highest in 180 kg/hm~2 nitrogen treatment;the application of nitrogen fertilizer had no effect on buckwheat amylose content,amylopectin content and fat content.Nitrogen application significantly increased the ratio of buckwheat granules to medium granules,reduced the proportion of large granules,and significantly reduced the solubility of 70~90°C buckwheat starch.The results of RVA showed that the gelatinization temperature of buckwheat starch increased under the nitrogen treatment,but the differences between nitrogen treatments were not significant.The peak viscosity,trough viscosity,breakdown viscosity,final viscosity and setback viscosity all decreased with the increase of application of nitrogen.Nitrogen application reduced the retrogradation rate of buckwheat starch paste and slowed the rate of retrogradation;the light transmittance of buckwheat increased with the increase of nitrogen application rate.Scanning electron microscopy showed that nitrogen application had no significant effect on the appearance of buckwheat starch.The activities of ADPGPase,SSS,GBSS and SBE in buckwheat kernels changed with a tendency at a single peak curve.The peak activities of ADPGPase,SSS and GBSS showed after 15 days of flowering,and the peak activity of SBE enzyme appeared in after 10 days of flowering.After 5 days of flowering,nitrogen treatment reduced the activities of ADPGPase,SSS and GBSS enzymes to a different extent or had no significant effect.The application of nitrogen after 10~20 days of flowering significantly increased the activity of ADPGPase,SSS and GBSS enzymes.The highest value appeared under 180 kg/hm~2 nitrogen or 270 kg/hm~2nitrogen treatment.There was no significant difference in the activity of ADPGPase,SSS and GBSS between the two treatments after 25 daysof flowering;the peak activity of SBE occurred after 10 days of flowering,and the treatment of 180 kg/hm~2 nitrogen and 270 kg/hm~2 nitrogen decreased the SBE activity of buckwheat seeds after 5~15 days of flowering.The SBE enzyme activity of buckwheat seeds treated with nitrogen after 20~25 days was greater than that of the control. |
