Effects Of Mid-stage Nitrogen Regulation On Yield And Quality Of Japonica Rice With Good Taste Quality And Its Physiological Mechanism

With the adjustment of China's agricultural industrial structure,accelerating the process of high-quality rice production has become the future development direction.In recent years,a variety of high-quality rice varieties have been introduced in the breeding field,among which the japonica rice with good taste quality represented by Nangeng 9108 and Nangeng 5055 in jiangsu province were excellent.However,due to the lack of systematic research and clarification on the rational fertilization of such new varieties,the japonica rice with good taste quality can neither be high yield nor high quality.The regulation of nitrogen fertilizer at middle growth stage is the key link of rice cultivation which has important influence on rice yield,quality and nitrogen utilization.Therefore,we conducted the experiment which set different application timing of panicle fertilizer in mid-stage for clarifying the characteristics and mechanism of yield and quality formation of japonica rice with good taste quality under different nitrogen fertilizer regulation,and exploring the law of fertilizer demand of high yield and high quality.The appropriate mid-stage nitrogen regulation for coordinating the yield and quality and increasing N utilization of japonica rice with good taste quality was summarized,and reasonable theoretical guidance for the cultivation of high yield and quality was provided.Field experiments were conducted in rice seasons at the modern agricultural park in Haian city,Jiangsu province,an off-campus experimental base of Yangzhou University during 2017 and 2018.The representative japonica rice varieties Nangeng 9108 and Nangeng 5055 in Jiangsu province were selected.Nine mid-stage nitrogen regulation measures was set,no panicle fertilizer was applied,and panicle fertilizer was applied once at emergence of the top-sixth-leaf,the top-fifth-leaf,the top-fourth-leaf,the top-third-leaf,the top-second-leaf and the top-first-leaf of the main stem,and panicle fertilizer was applied twice equally at emergence of the top-fifth-leaf and top-second-leaf,the top-third-leaf and the top-first-leaf of the main stem,as well as no nitrogen fertilizer was applied during the whole growth period as control treatment,respectively as N1,N2,N3,N4,N5,N6,N7,N8,N9,NO.The differences of rice yield and photosynthetic material production characteristics,rice quality characteristics,nitrogen and carbon metabolism characteristics,and grain starch physicochemical characteristics under different mid-stage nitrogen regulation measures were systematically compared.The main results were as follows:1.About yield and its components:Compared with N1 without panicle fertilizer,applying panicle fertilizer significantly increased the total spikelets and filled-grain percentage,then increased yield.With the delay of the application timing of panicle fertilizer,the panicle number of the two varieties decreased gradually,the filled-grain percentage and 1000-grain weight increased,the number of grains per panicle and yield increased first and then decreased,presented a parabolic trend,and reached the maximum value under the N4 treatment,i.e.panicle fertilizer was applied once at emergence of the top-fifth-leaf of the main stem.When panicle fertilizer was applied in batches,N8 treatment,i.e.panicle fertilizer was applied twice equally at emergence of the top-fifth-leaf and top-second-leaf of the main stem could stabilize the number of effective panicle and promote the big panicle,and showed higher yield then treatments that panicle fertilizer was applied once time.The maximum yield of two varieties treated with N8 was 37.2%-45.5%higher than that of N1,and 4.3%-4.8%higher than that of N4.Therefore,applying panicle fertilizer can significantly increase the total spikelets and yield by increasing the number of grains per panicle.The number of grains per panicle and the total spikiness were significantly increased and the filled-grain percentage and 1000-grain weight were maintained at a high level on the basis of sufficient effective panicle number when panicle fertilizer was applied twice equally at emergence of the top-fifth-leaf and top-second-leaf of the main stem,which increased rice yield.2.About dry matter accumulation and photo synthetic production:Compared with N1 without panicle fertilizer,applying panicle fertilizer in the first three stages could increase the number of tillers after jointing and leaf area index(LAI)at jointing stage.The effective and high-efficiency LAI at heading stage and LAI at maturity stage could be significantly improved by applying panicle fertilizer,and the dry matter accumulation at the two stages could be increased.When panicle fertilizer was applied once time,with the delay of the application timing,the number of panicle per unit area decreased gradually and the productive tiller percentage increased.LAI at jointing stage was increased by fertilization earlier treatment.The effective and high-efficiency LAI and leaf area ratio at heading stage presented a parabolic trend,then reached the maximum value under N4.The decreasing rate of leaf area in grain-filling stage decreased gradually.Therefore,N2 and N3 treatments,i.e.panicle fertilizer was applied once at emergence of the top-sixth-leaf and the top-fifth-leaf of the main stem,showed a faster decay rate.The dry matter accumulation at heading stage and mature stage,and the dry matter accumulation from jointing to heading stage and from heading to maturity stage increased first and then decreased,then reached the maximum value under N4 When panicle fertilizer was applied in batches,the effective and high-efficiency LAI at heading stage,the dry matter accumulation at heading stage and maturity stage were all the largest in N8,which were significantly larger than that of N4.The total dry matter accumulation of two varieties at N8 increased by 31.6%?35.7%compared with N1,and increased by 3.4%?4.4%compared with N4.Therefore,panicle fertilizer was applied twice equally at emergence of the top-fifth-leaf and top-second-leaf of the main stem or applied once at emergence of the top-fifth-leaf,which could improve rice population structure,effectively reduce the peak seedling,improve the productive tiller percentage,effectively reduce the decreasing rate of leaf area,at the same time keep higher LAI at the heading stage and mature stage,thus improve group photosynthetic capacity,promote dry matter accumulation and transportation,increase total biology yield and then increase rice yield.3.About rice quality:Compared with N1 without panicle fertilizer,applying panicle fertilizer significantly increased the indicators of processing quality namely the rates of brown rice,milled rice and head milled rice of the two varieties,decreased the indicators of appearance quality namely the chalkiness rice percentage,chalkiness area and chalkiness degree.Also it decreased the amylose content,and increased the protein content and gel consistency.While increased the hardness,it also reduced the appearance,viscosity,balance degree and taste value.When panicle fertilizer was applied once time,with the delay of the application timing,all indicators of processing and appearance quality increased,the amylose content of the two varieties decreased,while the protein content and gel consistency gradually increased.In addition to the hardness,the appearance,viscosity,balance degree and taste value all showed a decreasing trend.When panicle fertilizer was applied in batches,the processing quality of the N8 is inferior to that of the N9,while the appearance and cooking quality are superior to that of the N9.The the rates of head milled rice and protein content of two varieties at N8 increased by 3.0%?10.3%and 14.8%?16.5%respectively compared with N1 treatment.Therefore,applying panicle fertilizer nitrogen and delaying the application could improve the processing quality of rice,significantly improve the nutritional quality,but reduce the taste quality.Application of panicle fertilizer would improve the rice appearance quality,but delaying the application of panicle fertilizer nitrogen will lead to a drop in it.Applying panicle fertilizer at about the emergence of the top-fifth-leaf of the main stem is a more balanced fertilization scheme4.About nitrogen metabolism characteristics:Compared with N1 without panicle fertilizer,applying panicle fertilizer increased nitrogen content and nitrogen uptake at the heading stage and the mature stage,significantly increased the nitrogen accumulation from jointing to heading stage and from heading to mature stage,increased N translocation amount in leaves and N increase in panicle after heading.When panicle fertilizer was applied once time,with the delay of the application timing,nitrogen content at the heading stage and the mature stage increased,nitrogen uptake presented a parabolic trend,then reached the maximum value under N4.The nitrogen accumulation from jointing to heading stage and from heading to mature stage,nitrogen apparent use efficiency(NAPE),nitrogen physiological use efficiency(NPE),nitrogen agronomic use efficiency(NAGE)and partial factor productivity of applied nitrogen(PFP)increased at first and then decreased,then reached the maximum value under N4.N translocation amount in leaves and stem and N increase in panicle after heading presented a parabolic trend too.The N apparent translocation rate and N translocation conversion rate of stem decreased gradually.When panicle fertilizer was applied in batches,nitrogen uptake at the heading stage and the mature stage,nitrogen accumulation after jointing,and NAPE,NPE,NAGE were all the largest in N8,which were significantly larger than that of N4.The total nitrogen uptake of two varieties treated with N8 increased by 37.9%-42.3%compared with that in N1,and increased by 3.7%?6.0%compared with that in N4.Therefore,applying panicle fertilizer could increased nitrogen content and nitrogen uptake at heading stage and mature stage,and nitrogen accumulation after heading.Panicle fertilizer was applied twice equally at emergence of the top fifth-leaf and top-second-leaf of the main stem,which could ensure the nitrogen uptake before jointing,increase the nitrogen accumulation after jointing and the total nitrogen uptake at mature stage,at the same time promote the nitrogen translocation amount after heading,which was conducive to the improvement of yield and nitrogen utilization efficiency.5.About Carbon metabolism characteristics:With the application of panicle fertilizer and the delay of application timing,the concentration of NSC in leaves and stem decreased gradually during the whole grouting stage.The soluble sugar and starch concentration,and the C/N ratio in all organs decreased gradually at heading stage and mature stage.The proportion of NSC accumulation in panicle at heading stage and mature stage increased first and then decreased.The accumulation amount of NSC in stem at heading stage and mature stage,the NSC translocation amount and translocation rate of stem after flowering of the two varieties were all increased first and then decreased,and reached the maximum value under the N4 treatment.The soluble sugar and starch concentrations in the leaves were negatively correlated with brown rice rate,milled rice rate,head milled rice rate,gel consistency and protein content,but positively correlated with amylose content.The correlation between soluble sugar concentration in stem and rice quality was basically consistent with soluble sugar in leaf.The concentration of starch in stem was negatively correlated with brown rice rate and milled rice rate,but positively correlated with amylose content.Therefore,applying panicle fertilizer nitrogen and delaying the application will reduce the NSC content and C/N ratio of each organ of the plant,and can improve the processing quality and nutrition quality,but will reduce the cooking quality.Applying panicle fertilizer at about the emergence of the top-fifth-leaf of the main stem can increase the proportion of NSC accumulation in panicle,and the accumulation of NSC in the stem,as well as the NSC translocation amount and translocation rate of stem after flowering,which good for yield increase.6.About morphological structure and physicochemical properties of starch:With the application of panicle fertilizer and the delay of application timing,the values of D[3,2](surface area weighted mean diameter)and D[4,3](volume mean diameter)increased gradually,the proportion of small-and medium-sized starch granules presented increasing trend,whereas that of large-sized granules decreased gradually.The starch crystal type was not changed under different mid-stage nitrogen regulation measures,but the relative crystallinity increased gradually,and the apparent amylose content decreased,and the swelling power and water solubility gradually increased with the application of panicle fertilizer and the delay of application timing.In addition to the gradual increase of gelatinization enthalpy,the onset temperature,peak of gelatinization temperature,conclusion temperature,retrogradation enthalpies and retrogradation percentage all decreased.The peak viscosity,trough viscosity,final viscosity,breakdown viscosity and setback viscosity all decreased gradually,and the pasting temperature remained relatively stable between treatments.Therefore,applying panicle fertilizer nitrogen and delaying the application will reduce the content of large-sized granules,improve the relative crystallinity,the swelling power and water solubility,reduce the apparent viscosity of rice flour,increase the enthalpy of starch gelatinization,which resulting in the cooking quality decreased.Above all,the mid-stage nitrogen regulation for the influence of japonica rice with good taste quality is multifaceted and complex.The increase of the nitrogen accumulation after jointing,the total nitrogen uptake at mature stage and nitrogen use efficiency,the increase of the N translocation amount in stem and leaves after heading,the increase of the accumulation of NSC in the stem,the NSC translocation amount and translocation rate of stem after flowering,are the important mechanism characteristics of high yield in japonica rice with good taste quality under reasonable mid-stage nitrogen regulation.The relatively balanced carbon and nitrogen metabolism,the appropriate C/N ratio,the higher apparent viscosity of rice flour and the smaller relative crystallinity and enthalpy of gelatinization of rice starch are the mechanism characteristics of high quality in japonica rice with good taste quality.From the perspective of realizing the relative coordination between high yield and high quality,as well as the efficient use of nitrogen fertilizer,it is best to ensure panicle fertilizer application,and it should be applied twice equally at emergence of the top-fifth-leaf and top-second-leaf of the main stem.But if you consider simplify work times and pursue the eating quality,it should be applied once at emergence of the top-fifth-leaf of the main stem or slightly ahead of that.