【Objective】Pre-silking high temperature is likely to cause large negative impacts on maize yield, which is one of the important factors affecting ear development. This study was aimed to clarify the influence of pre-flowering high temperature on grain yield and ear development process, which was one of great significance for the stable and high yield of maize. 【Method】In this study, heat-resistant maize varieties Zhengdan958 and heat-sensitive maize varieties Lianchuang808 at flowering stage were used as research materials in artificial intelligence greenhouse, and then the influence of different high temperature of 40/30℃ and 35/25℃ on grain yield, ear development, ultrastructure of pollen and filament and photosynthetic characteristics from V9 to silking period were investigated.【Result】High temperature stress from V9 to silking period reduced the ear length, grain number and kernel weight of different genotypes summer maize, which led to a significant decrease in yield. Compared with control (35/25℃), the row grain number of Zhengdan 958 and Lianchuang 808 under high temperature significantly decreased by 22.21% and 24.59%, respectively; The kernel number per ear decreased by 29.85% and 27.80%, respectively; The thousand kernel weight decreased by 24.04% and 17.47%, respectively; The grain yield decreased by 44.98% and 40.88%, respectively. The dry weight of tassel, dry weight of ear, ear length and net photosynthetic rate of Zhengdan958 and Lianchuang808 under high temperature stress from V9 to silking period were significantly decreased 39.42% and 15.60%, 22.50% and15.56%,48.70% and 56.48% compared with control (35/25℃), respectively. The anthesis silking interval (ASI) of Zhengdan958 and Lianchuang808 increased to 7 d and 6 d as a result of delay of silking period rather than tasseling period. High temperature stress had obvious influence on the ultrastructure of maize pollen and filament surface of two maize varieties. Under high temperature stress, the surface of the pollen grain shriveled and collapsed, net vein protuberance and collapsed germinal aperture. At the same time, the filament surface shrank horizontally, the number of filament hair significantly reduced, and almost all residual filament hair lodged on the surface of the filament, which reduced the filament area of accepting the pollen.【Conclusion】High temperature stress from V9 to silking period were more serious on yield formation, photosynthetic characteristics and ear development of Zhengdan958 than Lianchuang808. High temperature stress from V9 to silking period significantly damaged the pollen and filament morphology, inhibited the development of tassel and ear, reduced the photosynthetic capacity, and decreased the kernel number per ear and kernel weight of two maize varieties, which significantly reduced the grain yield of maize. Therefore, the selection of maize varieties in field depended on the period of high temperature stress.
【Objective】Increasing density is one of the important ways to increase the yield of maize, but with the increase of planting density, it will usually cause the colony closure and the decrease of the utilization rate of light energy. Therefore, it is very important to explore and change the planting mode to weaken the negative effects of excessive density on plants and to improve the group canopy structure.【Method】The experiment was conducted in 2018 and 2019. Using Denghai 605 and Zhengdan 958 as test materials, two planting modes of parallel planting and staggered planting were set up under the two density conditions of 67 500 plants/hm2 and 82 500 plants/hm2. The effects of density on summer maize yield and photosynthetic characteristics were expected to explore and to understand the interaction mechanism of staggered planting and density, and to propose a suitable planting model for high-yield summer maize, which provided a certain theoretical basis for the scientific planting model of summer maize.【Result】Increased density reduced the uniformity of the population. The ear leaf net photosynthetic rate (Pn), photosynthetic key enzyme activities, and chlorophyll content were lower than those of low density, and the photosynthetic key enzyme activities decreased more with the growth period under high density. This meant that increasing the density would increase the leaf senescence rate, which was not conducive to plant photosynthesis. Under the staggered planting model, the group uniformity was improved, the angle between stems and leaves was increased, the leaves were more flat, the light energy interception rate was increased, the activity of Pn, photosynthetic key enzymes and chlorophyll content increased, the accumulation of dry matter in the population and the distribution of dry matter to the grain increased, thereby significantly increasing the yield. Staggered planting increased the average yield by 3.8%-6.1% compared to planting of the parallel plant. Staggered planting under the premise of ensuring the number of groups weakened the competition between individual plants within the group for light and temperature resources, ensured the full development of the individual development potential of maize, and enabled the coordinated development of maize groups and individuals.【Conclusion】Staggered planting could significantly improve the group canopy structure, optimize the group’s lighting conditions, enhance its photosynthetic performance and material production capacity, and increase maize yield. Under the conditions of this experiment, comprehensive analysis believed that the stagger planting model under 82 500 plants/hm2 density conditions performs was the best, which could provide a reference for the establishment of a high-yield model of summer maize.
【Objective】 The aim of this study was to explore the regulatory effects of expanding and shrinking cultivation models under different densities on the yield and population structure of Huang-Huai-Hai summer maize. 【Method】 The high yield maize variety Zhengdan958 was used as experimental material, three kinds of row spacing treatments, such as 60 cm (B1), 80 cm (B2), and 100 cm (B3), and two planting densities of 67 500 plants/hm2and 82 500 plants/hm2, were used to form different cultivation patterns through split zone design in 2018 and 2019. 【Result】 Compared with D1 density, D2 density could significantly increase the population leaf area and photosynthetic potential, improve the light energy utilization of the population, increase the dry matter accumulation of the population, and promote the increase of yield. Under the condition of different planting density, the effect of expansion and shrinkage on population structure was different. Under the density of 67 500 plants/hm2, the effect of expansion and shrinkage on the yield was not significant. Under the density of 82 500 plants/hm2, B2 treatment increased the yield by increasing the number of grains per row and 1000-grain weight, which was 9.45% and 11.48% higher than that of B1 and B3 treatments, respectively. B2 treatment significantly increased the population leaf area index (LAI), delayed the senescence of the middle and lower leaves, increased the photosynthetic potential of the population after anthesis, increased the angle between stems and leaves, and decreased the leaf orientation value. The light transmittance of leaf layer and bottom layer in panicle position increased significantly, the extinction coefficient decreased, the dry matter accumulation increased after anthesis, and the dry matter transfer decreased after anthesis. The results showed that under the condition of high density, the equal row spacing model of 80 cm expansion was beneficial to build an efficient photosynthetic population structure, delay leaf senescence, improve the photosynthetic performance of the population, increase the production and accumulation of dry matter of the population, and thus increase the yield. 【Conclusion】 The high-yield cultivation of summer maize in Huang-Huai-Hai Plain can achieve efficient utilization of light energy and synergistic increase in yield by increasing planting density and appropriate expansion and shrinking of plants. Under the experimental conditions, a planting pattern of 82 500 plants/hm2 with a density of 80 cm is recommended.
【Objective】With the decrease of cultivated land area, the increase of population and the rapid development of social economy, increasing crop yield per unit area is an important way to improve the total grain yield and ensure the food security in China. It is of great significance to explore the way of high efficiency and limiting factors to improve the unit yield. 【Method】 In this study, winter wheat and summer maize were taken as the research objects. In four ecological regions of Shandong province (eastern Shandong, central Shandong, northwestern Shandong and southwestern Shandong), the simulation model and other methods were employed to study yield under different climate and cultivation management conditions in 2008-2017, to put forward quantitative evaluation indicators, to analyze and clarify the main limiting factors affecting resource utilization and yield.【Result】(1) In the growth season of winter wheat in the eastern Shandong, the influencing rates of light and temperature resource, variety, cultivation pattern, water resource and nitrogen resource were 16.96%, 20.68%, 1.39%, 60.97% and 0, respectively, those in central Shandong were 37.72%, 20.16%, 1.57%, 40.55% and 0, and those in northwestern Shandong were 17.90%, 19.11%, 1.20%, 61.79%, 0, respectively; Those in southwestern Shandong were 33.65%, 23.80%, 1.65%, 40.90% and 0 respectively. (2) In the growth season of summer maize in the eastern Shandong, the influencing rates of light and temperature resource, variety, cultivation mode, water resource and nitrogen resource were 49.11%, 9.07%, 10.64%, 31.18% and 0, respectively; In central Shandong, the influence rates of each limiting factor were 56.62%, 10.86%, 11.65%, 20.87% and 0, respectively; In northwestern Shandong, the influence rates of each factor were 43.01%, 18.95% 11.26%, 26.78% and 0; Those in southwestern Shandong were 64.42%, 5.44%, 15.84%, 14.30% and 0, respectively. 【Conclusion】 In the winter wheat growing season, the farmland resources in the eastern and northwestern Shandong were mainly limited by water resource, followed by light and temperature resource and variety, and the cultivation mode and nitrogen resource had little influence. In the central and southwestern Shandong, it was mainly affected by light and temperature resource and water resources, followed by the variety factors. The growth season of maize in the four regions was influenced by light and temperature resource, followed by water resource, and less by varieties and cultivation patterns.
【Objective】In recent years, it is the limitation for summer maize to face the less light radiation during the growing season, and the light deficiency has become the main limiting factor affecting the production of maize. In this study, the row spacing under high density of maize was adjusted appropriately to improve the light in the canopy and the interior of the population and to alleviate the influence of shading caused by high density, so as to lay a foundation for further improving the yield.【Method】This experiment took Zhengdan 958 as the experimental material under field conditions in 2018-2019, and there were two different planting densities, which were 67 500 plants/hm2 and 82 500 plants/hm2, and three row spacing forms (60+60, 80+40, 100+20), with mulching reflective film (FM) and no film treatment (NM). The effects of mulching reflective film and row spacing on light energy utilization and yield of summer maize were studied. 【Result】As the density increases, the maize yield increased. There was no significant difference in the yield of “60+60” and “80+40” row spacing configurations when the density of 67 500 plants/hm 2 was higher than that of “100+20” row spacing configurations under the condition of mulching reflective film and no film. But at 82 500 plants/hm 2 density, the row spacing configuration of “FM80+40” under the mulching treatment could effectively improve the light environment within the population and made the distribution of light energy in the canopy more reasonable, and significantly increase the dry matter accumulation, LAI, canopy light interception rate, Pn and chlorophyll content; Compared with “FM60+60” and “FM100+20” treatments, the two-year average yield of which were increased by 6.6% and 10.8%, respectively. The yield of “NM80+40” row spacing was 5.8% and 8.7% higher than that of “NM60+60” and “NM100+20” row spacing, respectively, and the yield of “FM80+40” was 5.1% higher than that of “NM80+40”.【Conclusion】Under the density of 82 500 plants/hm 2, “80+40” row spacing arrangement supplemented by mulching reflective film could significantly improve the photosynthetic characteristics of summer maize, increase the reflectance of transmitted light at the lower part, and then increase the illumination of the middle and lower part of leaves, prevent premature aging of leaves, and improve photosynthetic capacity. Therefore, this treatment was an ideal cultivation mode to achieve high yield of summer maize
