Changes In Yield Capability And Population Structure Of Spring Maize Resulted Of Yield Improvements

The objective of this study was to provide a theoretical basis for maize production research by analyzing the maize yield gain characteristics by analyzing the population structure characteristics and yield capability of spring maize resulted of productivity improvements. Six varieties of maize were selected for the study; each selection is representative of a typical or commonly used maize variety from a specific decade, beginning from the1950's and continuing through each decade into the2000's. Each variety was planted under four different densities (37500,52500,67500, and82500plants ha-1) and four different nitrogen applications (0,150,225, and300kg ha-1) to study the effects on yield gain and Population Structure characteristics. The main results were as follows:(1)The obtained results demonstrated that there was a maize yield Grain yield has increased at a linear rate of120.34kg/ha between the1950's variety and the2000's variety. The effects of maize variety, nitrogen application, and planting density on yield were all significant. Modern Chinese maize varieties had a higher yield advantage. They also displayed the additional potential to acquire higher yield under increased planting densities and nitrogen applications. At the present cultivation levels (planting at67500plants ha-1with225kg ha-1nitrogen application), the contribution types and corresponding yield increase percentages were as follows:genetic improvement,45.37%; agronomic-management improvement,30.94%; and genotype x agronomic-management interaction,23.69%. At high-yielding cultivation levels (planting at82500plants ha-1with300kg ha-1nitrogen application), the contribution types and corresponding yield increase percentages were as follows: genetic improvement,31.30%; agronomic-management improvement,36.23%; and genotype x agronomic-management interaction,32.47%. The contribution of agronomic-management and genotype x agronomic-management interaction to yield increase would be larger with the corresponding management improvement. To further increase maize grain yield in China, researchers should further examine the effects of agronomic-management on maize yield and the adaptation of variety to agronomic-management.(2) The yield components were analyzed, which showed that plant barren ratio was decreased significantly with variety replacement, the plant barren ratio of Baihe was15.99%, and that of Xianyu335and Zhengdan958were0.23%和0.35%, Ear number per mu of modern varieties was increased significantly with increase of density; in this condition, kernel number per ear has increased at a linear rate of2.86grains, thousand kernel weigh has increased at a linear rate of1.194g with variety replacement, the yield was in increased of the combined action of ear number, kernel number and thousand kernel weigh. The increase of ear number was not because of increase of silks number, but because of increase of rate of granulation. Ear number and thousand kernel weigh were decreased with increase of plant density. The decrease of modern varieties' was less than early varieties'.The results of dry matter production and distribution showed that dry matter accumulation was increased with variety replacement, the increase of modern variety Xianyu335was higher than early variety Baihe58.76%. The dry matter accumulation of modern variety after anthesis was increased significantly. Dry matter accumulation of Xianyu335and Zhengdan958were51.59%,53.17%respectively, that of early variety Baihe was46.83%. The harvest index was increased with the yield increase. The harvest index of early variety Baihe was0.41, that of modern variety Xianyu335was0.53. The transfer rate of modern variety dry matter accumulation before anthesis to ear was lower than that of early varieties. The yield of modern variety was increased by producing more dry matter after anthesis. With the increase of density, the dry matter per plant was decreased but population dry matter production was increased, the changeable range of modern varieties was less than that of early varieties.(4) The difference of canopy structure between varieties released in different years. Leaf angle of modern varieties was decreased, the average leaf angle of modern variety Xianyu335was decreased by27.1%than that of early variety Baihe. LOV of modern varieties was increased, the average LOV of modern variety Xianyu335was increased by27.1%than that of early variety Baihe. The upper side leaves of plant became compact, lower part leaves of plant became loose, it was beneficial to transmission and distribution of light. The plan density and LAI of modern varieties with the highest yield were increased, such as suitable planting density of Baihe was37500plant/ha and the LAI of Baihe was3.7, suitable planting density of Zhengdan958was82500plant/ha and the LAI of Zhengdan958was6.2; suitable planting density of Xianyu335was82500plant/ha and the LAI of Xianyu335was6.1; the capacity for the resistance to lodging of modern varieties was improved significantly, Lodging rate of early variety Baihe was12.6%, Lodging rate of modern varieties Xianyu335and Zhengdan958were2.2%,1.1%respectively. Although it was also affected by plant density and nitrogen application, lodging rate of varieties released in different years was mainly determined by the genotype of variety.