Effects And Mechanism Of Precise-using Nitrogen On The Formation Of Super-high Maize Yield

Maize has been associated with the largest plant area and highest total yield among various cereal crops, contributing to approximately55%of China’s grain output. To study effects and mechanism of precise-using nitrogen on the formation of super-high maize yield, on the experimental fields of key laboratory of crop genetics and physiology of Jiangsu Province (Yangzhou, Jiangsu Province), Population-quality indices of super-high yield summer maize were investigated, and its main physiological mechanism were analyzed. The main results are as follows:1. Super-high yield level of summer maize and parameters of precise-using nitrogenThe yields of four maize hybrids (Xundan20, Suyu30, Suyu20and Suyu29) reached the peak at450kg ha-1nitrogen level, which were13850,13798,15455and16787kg ha-1, respectively. Their optional nitrogen amount was452.7,461.3,463.8and452.8kg ha-1, respectively. With the soil contained1.08g kg-1(Total N)and85.33mg kg-1N(available nitrogen), Grain production per kg N and N utilization efficiency of Suyu20were44.0kg and38.63%, Xundan20’ were47.8kg and35.52%, respectively.2. Dry matter production and photosynthetic characteristics of summer maize under super-high yield conditionsThe objective of this study was to reveal the effects of nitrogen treatments on yield, dry matter production and photosynthetic characteristics of summer maize under super-high yield (≥15000kg ha-1) conditions. An split plot design field experiment was conducted using three maize hybrids Suyu30, Suyu20, Suyu29as materials. Six nitrogen levels which were0,360,405,450,495and540kg ha-1respectively were designed in this study. Results showed:450kg ha-1nitrogen level increased the photosynthetic rate at anthesis stage, decreased magnitude of its decline during filling stage. And the maize population had a higher accumulation rate and a bigger amount of dry materials at450kg ha-1nitrogen level. The results analyzed by Richards model showed that the maximal accumulation rate of dry materials of three maize hybrids appeared at the first10days after anthesis stage and the later the higher yield; Suyu29among three maize hybrids which had the longest active growth period (up to25days after anthesis stage nearly) and the maximal accumulation of practical and theoretical dry materials had the highest yield. After comparing the maximal accumulation of practical and theoretical dry materials, we could know that Suyu20and Suyu29still had the great yield potential.3. Photosynthetic characteristics of summer maize at grain-filling stage under super-high yield conditions.450kg N ha-1materially improved maize yields, increased the net photosynthetic rate(Pn) at anthesis stage and the number of photons that can be captured and transforms the light into energy(particularly at the late stage of grain filling), decreased magnitude of the photosynthetic rate’s decline during filling stage. And the grain yield of summer maize had close relationships with photosynthetic parameters during filling stage, especially in Pn, effective quantum yield of PSII photochemistry ((?)psii), nonphotochemical quenching(NPQ)at the early stage, pigments at the middle and carotenoids (Car) at the late stage of grain filling. The authors accordingly held that the duration of strong photosynthetic capacity at filling stage played a significant role in building a high yield population of maize.4. Morphology characteristics of grain and plant of summer maize under super-high yield conditionsThe statistics results show that a parabolic relationship existed between the yields of three maize hybrids and N rates. The maximum yields turned up at the450N kg ha-1level, which are13798,14531and16787kg ha-1, respectively. The kernel weight per ear, grain length, grain width and the length of internode near ear are increased markedly under the450N kg ha-1, which are239g (take Suyu29for example),12.29mm,10.83mm,20.2°(above),43.3°(middle) and26.1°(below), respectively. The lengths of1st,2nd and3rd internodes and stem diameter are also increased, which are11.1,11.4,11.4and2.35cm, respectively, while the lengths of internodes near ear (7th,8th and9th internodes) are decreased, which are14.3,14.0and15.5cm, respectively. The N level does not have insignificant effect on the grain thickness. The yield and stem diameter show significant or extremely significant positive correlations with the lengths of1st,2nd and3rd internodes, but significant negative with the length of7th internode, and not insignificant with the other lengths of internodes. Therefore, big grain length and width can be used as indicators in breeding super high-yield of maize cultivars. In practical maize production, proper N application can be used effectively to regulate the lengths of1st,2nd,3rd and7th internodes, thus to build up the super high-yield population of maize through enlarged N sink and effective transfer to yield formation.5. Grain and starch granule morphology in superior and inferior kernels of maize in response to nitrogenUnder high density conditions(82500plant ha-1),450kgNha-1materially increased markedly lengths and widths of grains, the number of big starch granules, surface area and volume, decreased the variance between superior and inferior grains, as a results, improved the sink and yield of maize. Besides, the effect of nitrogen rates on inferior grains was higher than on superior grains, but the yield was most closely related to the size of starch granules of superior grains. What’s more, the distribution of starch granules of superior grains was very different from inferior grains’:superior grains had lower peak values of diameter of starch granules, but had a wider distribution than inferior grains; Starch granules of superior grains which had more polygonal shapes were bigger than inferior grains’, from inferior grains whose surfaces were smooth had sphere shapes. Maybe, this was another major cause of grain filling degree and1000-grain weight increased, which were propitious for increasing the production of maize.6. Changes of grain and starch granule morphology in superior and inferior kernels of summer maize during filling stage.450kg N ha-1materially significantly accelerated the formation of starch grains, prolonged the time of rapid growth of starch granules, and increased the proportion of big and polyhedron starch granules. In the same N treatment, inferior grains should be favorable in big starch granules growth, while starch granules of superior grains grow at the same time. Polyhedron starch granules were found in superior and inferior grains under450kg N ha-120d after anthesis, and starch granules of superior grain was bigger than inferior grains’, while sphere starch granules were found only. But polyhedron starch granules were found in all the treatments, and the difference between superior and inferior grains was minimum under450kg N ha-1than20d after anthesis. Compared with0kg N ha-1,450kg N ha-1materially significantly prolonged the time of rapid growth of starch granules, maybe, this is the main reason of formation of super high yield. 7. Changes of molecular weight distribution and key enzyme activity in composing starch in superior and inferior kernels of summer maize during filling stage.With the grain filling, the activities of four key enzymes (AGP, SSS, GBSS, and SBE) showed a curvilinear change in superior and inferior grains in30d after anthesis with a peak value at20-25d after anthesis. The proportion of lower molecular weight branches of starch of superior grains tapered off with grain filling, while large molecular weight grow increasingly, but no significant changes were observed in molecular weight of inferior grains.450kg N ha-1materially increased markedly4key enzyme activity, decreased magnitude of its decline during filling stage, postponed the time of peak;450kg N ha-1also increased markedly the proportion of middle peak (B and C style branches of amylopectin)of GPC(gel permeation chromatography), accelerated the formation rate of lower molecular weight branches (A style branches) of starch, the effect of nitrogen rates on molecular weight distribution of inferior grains was higher than on superior grains’, and with a peak value at20-25d after anthesis, but had no effect observed markedly on the length of amylose. And there was no big difference observed between the length of amylose of superior and inferior grains.8. Changes of the content of hormone in superior and inferior kernels of summer maize during filling stage.The content of hormone (Z, ZR, GA3, and IAA) showed a curvilinear change in superior and inferior grains in30d after anthesis with a peak value at20-25d after anthesis. High content of hormone (Z, ZR, GA3, and IAA) promoted kernel growth. But content of ABA gradually built up, and content of ethylene decreased gradually. Yield and content of ABA and ethylene showed a negative relationship. Big difference between content of hormone of superior and inferior grains was observed. Compared with superior grains, peak concentrations of inferior grains came5d behindhand, and its decline after anthesis was faster.450kg N ha-1materially increased markedly four key enzyme activity, decreased magnitude of its decline during filling stage, postponed the time of peak.450kg N ha-1materially increased markedly contents of Z, ZR, GA3and IAA, decreased contents of ABA and ethylene. The effect of nitrogen rates on molecular weight distribution of inferior grains was higher than on superior grains’ and with a peak value at20d after anthesis usually. Sum up, it is important to control the hormone contents at20d after anthesis. 9. The relation among nitrogen levels, superior and inferior grains of maize and yieldThe relation among nitrogen levels, yield and superior and inferior grains of maize were closely relative. Compared with superior grains, the super high yield of maize mainly depended on the following respects of inferior grains:smaller variances between superior and inferior grains; bigger lengths and widths of grains, surface area and volume; earlier and more polyhedron starch granules; larger molecular weight and more branches of starch; stronger activity of4key enzymes (AGP, SSS, GBSS and SBE) and higher concent of4hormones (Z, ZR, GA3and IAA); smaller decline of activity of key enzymes and concent of4hormones during late filling stage(20d after anthsis).