Research On Maize?Zea Mays L.? Ideotype And Canopy Structure With Yield Potential Of 22.5 T Hm^-2

There were abundant solar and thermal resources at Qitai Farm?89°34?E,44°12?N?in Xinjiang,China.Total of 300 maize cultivars were used for high yield exploration in the latest 15 years with sufficient water and fertilizer to avoid stress,however,yields of different cultivars showed great difference and the highest grain yield was more than 22.5 t hm^-2,and some of them were less than 15.0 t hm^-2 with a yield gap of more than 50%.In this study,we selected six cultivars with highest yield in latest 10 years to study the plant type and canopy structure,N uptake and distribution in the canopy as well as the optimum LAI,the main results were as follows:1.Maize hybrid DH618 had obtained the highest yield in 2013,and was selected for field experiments to study the plant and canopy structure at 120,000 plants hm^-2 and 135,000 plants hm^-2 in 2014 and 2015.With the study of canopy structure,our results primarily explicited the canopy characteristics of plant type and canopy structure as follows:the dry matter gain was 20.0 and 36.5 t hm^-2 during post-silking and at maturity,the average transfer rate from vegetation organs was 8.7%,and the average harvest index was0.54 in the two experiment years.The average maximum LAI was 7.53 at silking,the leaf area was3.99×10³ cm² and 1.90×10³ cm² above and below the ear,and the spatial density of leaf area was 0.17cm² cm^-3 and 0.08 cm² cm^-3 above and below ear,respectively.The average light transmissions were 3.7%and 1.1%at the ear and bottom,respectively,and the average attenuation coefficient was 0.63.The plant height and ear height were about 287 and 113 cm.The average leaf orientation values were 51.9 and 49.2above and below ear,respectively.2.We selected maize cultivar DH618 with yield potential of 22.5 t hm^-2,and using data from previous publications to observe N characteristics under different yield levels and compare the experimental results with existing studies.The relationship between radiation and N distribution in the canopy of high-yield maize was also assessed.With the study on the relation of light and nitrogen in the canopy,we found that nitrogen uptake was significantly correlated with grain yield.However,N uptake per unit grain yield and grain N concentration at maturity decreased as grain yield inceased.The positive correlations between solar radiation and leaf and stalk N concentrations at silking showed that N concentration at silking increased as the height of the canopy layer increased because of increased solar radiation in the canopy.These results indicate that maize hybrids with erect upper leaves and high post-silking N uptake can coordinate and optimize the distribution of solar radiation and N in different canopy layers and thus improve yield and NUE under high-density.3.Six maize hybrids?SC704,ZD958,LY66,XY335,DH618 and MC670?with highest yield in different years in China were selected for the study of morphological traits,the results showed that the plant height and ear height decreased significantly,respectively,as well as the ear ratio?0.35-0.36?.Leaf angle above ear?15.0°-17.6°?and below ear?30.5°-32.4°?,leaf area per plant and LAI at silking decreased significantly.Leaf number above ear,average internode length above ear,SDLA and,the LOV above ear,LAI at maturity increased significantly,respectively.Light transmission at the bottom of the canopy?3.2%-3.8%?and transmission at the ear?18.6%-19.4%?also increased with the increase of yield potential.With these changes in morphological traits,there was better light condition above ear in high yield potential hybrids under high density.Based on this,we put forward the parameters of maize ideotype with yield potential of 22.5 t hm^-2,which provided references for ideotype breeding.4.To create populations with different leaf area index,different number of leaves were removed under high density after silking by using two cultivars with different plant type,ZD958?compact?and DH618?more compact?.The results showed that optimum leaf removal could increase maize grain yield,the leaves were redundancy under high density.The average LAI was 5.9?5.6 for ZD958 and 6.2 for DH618?in the treatments with highest grain yield in the two years.The light distribution,photosynthesis rate,stomatal conductance,dry matter especially post-silking dry matter accumulation had greater increase for cultivar ZD958 than DH618 after leaf removal.In the future maize breeding,compact cultivar should have smaller leaf area of topmost leaves or less number of leaves above ear or quickly senesced lower leaves after silking to decrease leaf area to improve light distribution in the canopy,however,for the more compact cultivar,leaves below ear should be senescent quickly after silking to reduce leaf respiration.