Formation Mechanism And Regulation Of Super-high-yielding Population In Wheat Following Rice

Wheat populations at two different yield levels in rice-wheat rotation, including high-yield population (8000kg～8500kg·hm-2, hereinafter as HY) and super-high-yield population (9100kg～9400kg·hm-2, hereinafter as SHY), were established by agronomic management on the medium-gluten wheat, Yangmai20(Triticum aestivum L.). From2010to2012, the field experiments were conducted at32combinations of two planting densities (150×104·hm-2and225×104·hm-2), two applications of nitrogen amount (210·hm-2and262.5kg·hm-2), two nitrogen applied ratios of basis:tillering:elongation:booting (3:1:3:3and5:1:2:2), and four nitrogen topdressing stages (flag leaf stage, booting stage, heading stage and anthesis). This study investigated the differences between HY and SHY in grain yield components and population formation indexes. In addition, the characteristics of nutrient accumulation, distribution and utilization, carbon-nitrogen metabolism and photosynthetic were analyzed. By analyzing and evaluating the effects of different cultivation technologies on fertilizer use efficiency, wheat quality and economic profit, the best cultivation technology achieving SHY was proposed. These could provide theoretical and technological support for wheat high-yield and super-high-yield production in the middle and lower reaches of the Yangtze River. The main results are as follows:(1) The results of two testing years consistently showed that, the synchronous increase of number of ears, grains per spike and1000-grain-weight was the key point in achieving SHY. On the basic of right ear number, the synchronous increase in grains per spike and1000-grains-weight was the strategy for achieving SHY. The number of ears, grains per spike and1000-grain-weight of SHY were510±20×104·hm-2,48±1.5and37±2g, respectively.(2) In terms of results, the structural characteristics of SHY were explicit. For SHY, on the basic of suitable stems and tiller dynamics, the ratio of No. of stems and tillers at the beginning of wintering stage to No. of ears, No. of stems and tillers at elongation stage and percentage of effective stems were0.9～1.3,1250×104～1500×104·hm-2and about40%, respectively. The LAI of SHY at the stages of booting, anthesis and maturity were6.5～7.0,5～6and4～4.5, respectively. And post-anthesis LAI was maintained higher as compared with HY. Besides, the moderate increase in dry matter accumulation amount (DMAA) from booting to anthesis, especially the increase in DMAA after anthesis, laid a solid material foundation for the construction of SHY. The DMAA of SHY during the interval from booting to antheis and from anthesis to maturity were2900kg～3600kg·hm-2and7200～7600kg·hm-2, separately. The dry matter amount of SHY at anthesis and at maturity were12500kg～13700kg·hm-2and19500kg～21000kg·hm-2, respectively. The contribution rate of post-anthesis DMAA to yield of SHY was around90%. Coefficient of economics (HI) of SHY was around0.4.(3) The results also showed that N, P and K accumulation amounts (hereinafter as NAA, PAA and KAA) of SHY before elongation were suitable. And during the interval from emergencing to elongation, there were no observable differences in these parameters between HY and SHY. From elongation to anthesis, at anthesis and at maturity, NAA, PAA and KAA of SHY were higher than those of HY. Compared with HY, NAA, PAA and KAA of SHY in grains at maturity were higher. N translocation amount (NTA) of SHY from vegetative organ at anthesis to grain was higher as compared with HY, but P and K translocation amount (PTA and KTA) were relatively suitable. In terms of the two parameters (a) N, P and K amounts producing100kg grain and (b) the use efficiency and harvest index of N, P and K, there were no significant differences between HY and SHY.(4) The mineral nutrition diagnosis indexes for SHY were suggested as follows:NAA at elongation, from elongation to anthesis, at anthesis and from anthesis to maturity were84kg～98kg·hm-2,104kg～117kg·hm-2,195kg～205kg·hm-2,37kg～49kg·hm-2and234kg～246kg·hm-2, respectively. And NTA from total organs were138kg～144kg·hm-2.PAA at elongation, from elongation to anthesis, at antheis, from anthesis to maturity and at maturity were17kg～21kg·hm-2,28kg～31kg·hm-2,46kg～50kg·hm-2,18kg～24kg·hm-2and66kg～74kg·hm-2, respectively. And PTA from total organs were23kg～26kg·hm-2.KAA at anthesis and at maturity were430kg～450kg·hm-2and366kg～408kg·hm-2, respectively. And KTA from total organs was91kg～100kg·hm-2.The N, P and K amount producing100kg grain were2.87kg～3.04kg,0.82kg～0.85kg and4.57kg～4.87kg, respectively. N, P and K use efficiency were32.93kg～34.86kg·kg-1,113.60kg～121.28kg·kg-1and20.56kg～22.02kg·kg-1, respectively. In addition, N, P and K harvest index were0.72～0.77,0.64～0.67and0.095～0.112, respectively.(5) Soluble sugar content, nitrogen content and soluble sugar to nitrogen ratio (hereinafter as C/N) dynamics in SHY plants were analyzed. Compared with HY, from the beginning of wintering stage to elongation, soluble sugar content and nitrogen content in SHY plants were higher, and C/N was relatively suitable. From booting stage to anthesis, soluble sugar content and nitrogen content in SHY plants were higher. After anthesis, SHY plants could accumulate more carbon. But at maturity, C/N in SHY plants was lower as compared with HY.The carbon-nitrogen nutrition diagnosis indexes for SHY were suggested. At the stages of booting, anthesis, milk-ripe and maturity, soluble sugar content were14.56%～16.78%,14.52%～16.82%,10.59%～11.23%and1.62%～1.76%respectively, nitrogen content were1.55%～1.64%,1.47%～1.57%,1.28%～1.30%and1.15%～1.20%, respectively, and C/N were9.37～10.25,9.80～10.69,8.29-8.77and1.41～1.48, respectively.(6) Flag leaves photosynthetic and senescence characteristics of SHY were clarified. Compared with HY, SPAD reading, photosynthetic rate (Pn) and the activities of SOD, POD and SOD in flag leaves after anthesis were higher, but MDA content was lower. These differences between SHY and HY were more significant at grain-filling stage (from the14th to28th day after anthesis). At grain-filling stage, in flag leaves of SHY, SPAD reading and Pn declined slower, the activities of SOD, POD and SOD were higher, and MDA content was lower as compare with HY.(7) A preliminary cultivation technology achieving SHY was developed. There were four cultivation technical combinations achieving SHY. The best was the combination of planting density225×104·hm-2, nitrogen amount210kg·hm-2, nitrogen applied ratio of basal:tillering: jointing:booting3:1:3:3and topdressing nitrogen at flag leaf stage, which could achieve SHY in different climatic type year. The other combinations could achieve SHY only in normal climatic year, i.e., combination of planting density150×104·hm-2, nitrogen amount262.5kg·hm-2, nitrogen applied ratio3:1:3:3and topdressing nitrogen at booting stage, and combinations of planting density225×104·hm-2, nitrogen amount262.5kg·hm-2, nitrogen applied ratio3:1:3:3and topdressing nitrogen at flag leaves stage or booting stage.The SHY cultivation technology system was established as follows. The suitable seeding date is around1st November. The seeds are sown at a planting density of225×104·hm-2by drill sowing, with a line spacing of30cm and a seedling depth of3cm～5cm. The applied amount of N, P and K are kept at210kg·hm-2,126kg·hm-2and126kg·hm-2, respectively, with an nitrogen application ratio of3:1:3:3at the stages of basal, tillering, jointing and booting. The fertilizer at the stages of basal, tillering, jointing and booting should be applied before sowing, at the4th leaf stage, at the remaining leaf age of2.5, and at the flag leaf stage or booting stage. Half amount of P and K is applied before sowing, and the remained half is applied at the remaining leaf age of2.5. (8) Fertilizer use efficiency, grain quality and economic profit of SHY technology were also evaluated. Among32combinations in the experiments, the best combination achieving SHY (planting density225×104·hm-2, nitrogen amount210kg-hm-2, nitrogen applied ratio3:1:3:3and topdressing nitrogen at the flag leaf stage) was generally better. In consequence, for SHY best combination, nitrogen agronomic efficiency (NAE) and nitrogen fertilizer use efficiency (NUE) were highest, and utilization efficiency (NUTE) and nitrogen harvest index (NHI) were generally high. The SHY cultivation technology didn’t severely affect grain processing quality and flour pasting parameters. Grain protein content, wet gluten content and flour yield, flour trough viscosity, peak time and pasting temp were even increased. Compared with other combinations, the SHY best combination could achieve the highest economic profits at a relatively low total cost.