Formation And Physiological Characteristics Of High-Yielding Population And Regulation Techniques With Plant Density And Nitrogen Application In Late-Sowing Wheat Following Rice

The middle and lower reaches of the Yangtze River winter wheat region is one of the main areas of wheat production in china.The increase of the yield in wheat following rice contributes a lot to the food security in China.Due to the popularization and application of middle-late maturing rice and postponed maturity,the sowing area suitable for winter wheat was dramatically reduced.The area of late and super-late sowing wheat increased yearly,which seriously restricts the development of winter wheat production.This contradiction is particularly significant in rice-wheat rotation area in Jiangsu province.It has become a hot issue widely focused by crop culture scientists.Lots of effects has been dedicated to study the causes of late sowing,the structure.ecology and the production conditions of planting,variety selection and relevant cultivation techniques,aiming to find a breakthrough in the theory and technology of high yield of late-sowing wheat.A field experiment was conducted to establish different populations by agronomic management under late-sowing condition in the Yanjiang region of Jiangsu?approximately 10 days later for a more suitable sowing date?and super-late sowing condition in the Lixiahe region?more than 30 days for a more suitable sowing date?.The indicators including the yield structure,population characteristics,nutrient utilization patterns,photosynthetic senescence characteristics and physiological mechanisms,and economic profits of high-yielding population of 8000kg·hm^-2 of late-sowing wheat and medium high-yielding population of 6750kg·hm^-2 of super-late sowing wheat were investigated to explored the high-yielding and high-quality cultivation technology system of late-sowing and super-late sowing wheat,providing theoretical and technological support for late sowing and super-late sowing wheat following rice.The main results were as follows:1.Late sowing and super-late sowing wheat following rice varietiesEight wheat varieties?Ningmai 14,Ningmai 19,Sumai 188,Yangmai 16,Yangmai 22,Yangfumai 4,Yangmai 23?were selected to study the adaptation mechanisms under late-sowing condition in the Yanjiang region of Jiangsu and super-late sowing condition in the Lixiahe region.It was recommended to choose Yangmai 23 and Yangfumai 4 for the target yield of 8000 kg·hm^-2 under late sowing condition.Yangmai 23 and Yangfumai 4 showed consistent higher dry matter accumulation,coordinated population structure,and larger leaf area index?hereinafter as LAI?at early growth.Also,the chlorophyll content and net photosynthetic rate after anthesis were significantly higher,which is beneficial to grain filling and imultaneously vest winter wheat with strong lodging resistance.Yangmai 22 and Yangmai 23 were recommended for the target yield of 6750 kg·hm^-2 under super-late sowing condition.Yangmai 22 had a strong tillering ability resulting more panicles.The average yield of Yangmai 22 was 7200.38 kg·hm^-2,with high yield potential and good stability.The two-year average yield of Yangmai 23 was 710⁴.62 kg·hm^-2.The population structures of Yangmai 22 and Yangmai 23 were coordinated throughout the whole growth period,with the observation of earlier grain-filling,higher grain filling rate,rapid completion of grouting,ultimately avoiding high temperature induced maturity.Although Yangmai 16 thrived in early growth stage,and has the characteristics of high grain filling rate,good yield stability and early maturing,the number of spike was difficult to increase under super-late sowing condition,which limits its yield potential.2.The quality characteristics of high-yielding population in late-sowing wheat and medium high-yielding population in super-late sowing wheatUnder late sowing condition,the structural characteristics of high-yielding population(above 8000 kg·hm^-2)were as follows:the number of spikes,grains per spike,1000-grain-weight and total grains were 560×10⁴·hm^-2,39.0?40.0,37.0g and 22000×10⁴,respectively.The main characteristics of the population showed that the ratio of No.of stems and tillers at the tillering,jointing and anthesis stage to No,of ears at maturity were 1.1?1,3,2.3?2.5,1.1?1.2 and earing percentage of stem and tillers was 40%,respectively.The dry mass at anthesis,maturity and from anthesis to maturity were 15000 kg·hm^-2,21000 kg·hm^-2 and more than 6200 kg·hm^-2,respectively.The LAI at the stages of booting,anthesis and milky were about 7.0,5.6 and 3.2,respectively and the ratio of grain to leaf?grain number/leaf and grain weight/leaf?were 0.31?0.33cm^-2 per grain and 11.5?11.8 mg · cm^-2,which was conducive to archive high yield.Under the condition of super-late sowing,the structural characteristics of medium high-yielding population(6750 kg·hm^-2)were as follows:the number of spikes,grains per spike,1000-grain-weight and total grains were 510xl×14·hm^-2,36.0-40.0,40.0g and 18500×10⁴,respectively.The main characteristics of the population performed that the ratio of No.of stems and tillers at the tillering,jointing and anthesis stage to No.of ears at maturity were 1.4?1.5,2.6?2.7,1,3?1.4 and earing percentage of stem and tillers was 3 8%,respectively.The dry matter amount at anthesis,maturity and from anthesis to maturity were 13500?14000 kg·hm^-2,19000 kg·hm^-2 and more than 5300 kg-hm"2,respectively.The LAI at the stages of booting,anthesis and milky were about 7.5,5?5.5 and 2.8-3.3,respectively and the grain leaf ratio?grain number/leaf and grain weight/leaf?were 0.25?0.26cm^-2 per grain and 9.2?10.0 mg·cm^-2.3.Nitrogen-accumulation characteristics of high-yielding population in late-sowing wheat and medium high-yielding population in super-late sowing wheatThe ¹⁵N study showed that,under the late sowing condition,soil nitrogen is the main resource for winter wheat during the anthesis and mature stages.The uptake of ¹⁵N was mainly from basal ¹⁵N at anthesis stage,and the absorption proportion of topdressing ¹⁵N was higher than the basal ¹⁵N at maturity stage.¹⁵N was transported from vegetative organs into grains after anthesis,and the transfer of nitrogen was mainly basal ¹⁵N.The topdressing ¹⁵N uptake and the proportion of total nitrogen significantly increased with the density increase in plants at maturity.Under high density conditions,due to the topdressing ¹⁵N transported from vegetative organs into grains,the nitrogen accumulation in grains increased consequently.It was shown that moderately increasing density under late sowing condition was beneficial to increase nitrogen uptake,reduce fertilizer residues in soil,and increase the nitrogen level from vegetative organs into grains.That is to say higher density helps to increase nitrogen fertilizer efficiency.N accumulation amounts?short for NAA?of late sowing high-yielding population(8000 kg-hm^-2)at booting stage,anthesis and maturity were 120.0?130.0 kg-hm^-2,170.0?190.0 kg·hm^-2and 230.0?250.0 kg·hm^-2,respectively.NAA from jointing stage to booting stage and from anthesis to maturity were 50.0?55.0kg·hm^-2 and above 50.0kg·hm^-2 respectively.Except for partial factor productivity of nitrogen fertilizer?PFPN?,other N efficiency indicators such as agronomic efficiency of N fertilizer?NAE?,nitrogen physiological efficiency?NPE?of high-yielding population were not significant difference with medium high-yielding population.NAA in super-late sowing medium high-yielding population(6750 kg·hm^-2)at booting stage,anthesis,maturity,and from anthesis to maturity were 95.0?100.0 kg·hm^-2,170.0 kg·hm^-2,210.0 kg·hm^-2,and 45.0 kg·hm^-2,respectively.N uptake amounts from jointing to booting and from booting to anthesis were 35.0?45.0 kg·hm^-2,70.0?75.0 kg·hm^-2,respectively.NAE and NPE of mediu high-yielding population were higher than medium yielding and low yielding population,the nitrogen transport capacity of the plants was higher.4.Photosynthetic and senescence characteristics in late sowing population and super-late sowing populationThe population of late sowing wheat with 8000 kg·hm^-2 yield had high SPAD values and net photosynthetic rates?Pn?,especially at the milky stage.Chlorophyll concentration and net photosynthetic rate in flag leaves were around 43.0?47.0 and 16.0umol·m^-2·s^-1.The chlorophyll concentration and activities of POD?Peroxidase?,CAT?Catalase?and SOD?Superoxide dismutase?of high-yielding population was higher than medium high-yielding population,MDA?Malondialdehyde?performed oppositely and the difference was more significant with the increase of flowering days.The correlation analysis showed that chlorophyll concentration net photosynthetic rate significantly correlates with yield.The population of super-late sowing wheat with 6750 kg·hm^-2 yield had high SPAD values and net photosynthetic rates?Pn?,chlorophyll concentration and net photosynthetic rate at the milky stage were around 35.0?37.0 and 14.5 umol·m^-2·s^-1,and the correlation analysis showed that SPAD value are significantly and positively correlated with activities of POD,CAT and SOD,while significant negative correlation with MDA content was observed.The activities of POD,CAT and SOD of medium high-yielding population was higher than low yield population,therefore it helps to delay leaf senescence and prolong the duration of photosynthetic function.5.The characteristics of C/N ratio of flag leaves in high-yielding population in late-sowing wheatThe ratio of soluble sugar to nitrogen?C/N?in flag leaves increased at postanthesis,and the C/N in flag leaves of high-yielding population was lower than other populations on 21 days and 28 days after anthesis significantly.The nitrogen content,activities of nitrate reductase?NR?and glutamine synthetase?GS?in the flag leaves of high-yielding population(8000 kg·hm^-2)were higher than those of medium high-yielding population.The results indicated that the nitrogen production capacity was significantly higher in the high-yielding population(8000 kg·hm^-2).The sucrose content of high-yielding population in flag leaves were lower than medium high-yielding population significantly at anthesis.Sucrose synthesis ability of high-yielding population was upregulated,hence the sucrose content of high-yielding population was significantly higher than that in medium high-yielding population after 14 days postanthesis.The activity of SS and SPS were consistent with the sucrose content.Correlation analysis showed that there was significant positive correlation between SS,SPS activity and sucrose content in flag leaves.6.The characteristics of lodging resistance in late-sowing wheatUnder late sowing conditions,the increase of plant density affected the internode length and plant height,and decreased the weight per unit length of the basal internodes and the accumulation of soluble sugar and lignin in the stem,finally impaired the lodging resistance of wheat.Reducing nitrogen application amount and ratios could effectively reduce the plant height and basal internodes,increase filling degree of basal internodes and key enzyme activity in lignin synthesis and improve lignin content of 2nd basal internode,and effectively enhance lodging resistance.Correlation analysis showed that lodging resistance index had a significant negative correlation with plant height,lodging coefficient,internode length and internode length below ear,the correlation coefficients were-0.64*,-0.94**,-0.92**,-0.70**,respectively,while it significantly and positively correlateed with the dry weight per unit length of 1st and 2nd basal internodes.It was shown that the lignin content in the 2nd internode after elongation for 40 days was significantly and positively associated with lodging resistance index,PAL and TAL activities.Therefore,the cultivation technical combination of late-sowing wheat as planting density 270×10⁴·hm^-2,nitrogen fertilizer 225 kg·hm^-2,nitrogen applied ratios of basis:tillering:Jointing:booting 4:2:1:3 were beneficial to control lodging and achieve high yield.7.High-yielding cultivation measures in late sowing and super-late sowing wheatIt was clarified that significant differences exists between different cultivation measures of late sowing and super-late sowing wheat.The cultivation combination was as follows:planting density 270×10⁴·hm^-2,nitrogen fertilizer 225 kg·hm^-2,nitrogen applied ratios of basis:tillering:Jointing:booting 5:1:2:2 or 4:2:1:3,P and K fertilizers 90 kg·hm^-2.Yangumai 4 and Yangmai 23 could obtain target output above 8000 kg·hm^-2 under late sowing condition in the Yanjiang region of Jingsu.When the cultivation combination was:planting density 330×10⁴·hm^-2,nitrogen fertilizer 225 kg·hm^-2,P and K fertilizers 90 kg·hm^-2,nitrogen applied ratios of basis:tillering:Jointing:booting 5:1:2:2 or 6:0:2:2,Yangmai 22 and Yangmai 23 could obtain target output above 6750 kg·hm^-2 under super-late sowing conditio1 in the Lixiahe region.