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Lodging is a common problem during maize production. Maize harvested at physiological maturity stage in traditional maize production. Previous researches about maize lodging also focused on stalk development process and some stage before the physiological maturation. There was less lodging research after physiological maturity. Mechanical grain harvest usually was carried out two to four weeks after the physiological maturity. Lodging made mechanical grain harvest become difficulty and increased harvest costs, and it also increased grain losses and decreased the grain quality. Maize lodging was a limiting factor in application of mechanical grain harvest technology. This paper reviewed the physiological changes in the maize senescence process and the influences factors on maize lodging, and proposed the measures and suggestions about improving maize lodging resistance during mid and late stage. Analysis showed that, natural senescence of maize from physiological maturity to harvest decreased activity of leaves, stalk and root, and made all of stalk moisture, water-soluble carbohydrate content, hemicellulose content and total structural carbohydrate content decline. These resulted in cell wall thinning, cell gap widening, and stalk strength and disease resistance decrease. The enzymatic activity of PAL, POD and PPO was low, which made the disease resistance decline. The stalk rot pathogen produced cell wall degrading enzymes to decompose cellulose and collapse the cells in stalk. The fungal hyphae flew through the plasma membrane and entered into epidermis cell, cortex and vascular bundle tissue. The stalk rot then increased the speed of stalk dehydration and drying shrinkage, and degraded the pith tissue. Maize stalk became hollow, softening and rot. This decreased stalk quality. Higher grain and full mechanization technologies required high population and delayed harvest to grain dehydration in the field. These accelerated and extension the aging process of maize, further decreased the stalk quality and disease resistance, and increased the lodging risk of maize after physiological maturity. In order to resolve the lodging problem and to accelerate development and promotion of maize mechanical grain harvest technology in China, we suggested that: (1) Theoretical research of maize lodging during late stage should be strengthened; (2) Germplasm creation should be strengthened to breed new maize cultivars with early-maturity, density-tolerant, high rate of grain dehydration, and strong stress resistance; (3) Common methods should be developed to obtain high-quality maize populations and reduce lodging during late stage including constructing a high-quality plow layer, suitable cultivars for grain mechanical harvest, rational close planting, scientific irrigation and fertilization, application of plant growth regulators, and insect-disease prevention; (4) Integration countermeasures should also be established according to ecological conditions in different maize regions.
【Objective】 The high grain dehydration rate and the low grain moisture content at harvest are two ear characters, which can be established for maize mechanical grain harvesting. Ear characters are decided by genes and have close relationship with grain dehydration. This internal relationship and the key ear characters that can characterize the traits of grain dehydration remain unknown, which are of great significance for breeding and screening of suitable varieties. 【Method】 The report researched on a total of 22 main cultivars of summer maize in HuangHuaiHai plain, and their ear characters were divided into 41 parameters covering bract, grain, cob and ear-pedicel. In 2015 and 2016, these parameters were measured and were used in correlation analysis with five grain parameters describing the dehydration rate, including the grain dehydration rate before physiological maturity (GDRbpm), the grain dehydration rate after physiological maturity (GDRapm), the total grain dehydration rate (GTDR), the grain moisture content at physiological maturity (GMCpm) and at harvest (GMCh). 【Result】 These 41 parameters were significantly different between the 22 cultivars, and there were some parameters significantly linked to grain dehydration. The bract length had a significantly negative relationship with GDRapm and a significantly positive relationship with GMCh. The value of “bract length/ear length” had a significantly negative correlation with GDRapm. The ear angle was positively correlated to GTDR at a significant level. The cob moisture content at physiological maturity had significantly positive relationships with GMCpm and GMCh. The grain number per ear was positively correlated to GDRbpm and GTDR at a significant level. The value of “ear length/grain number per row” had significantly positive relationships with GDRbpm, GDRapm and GTDR and had a significantly negative relationship with GMCh. The 100-grain dry weight at physiological maturity was negatively correlated to the grain moisture content at the significant level. There were no significant correlations between the other ear parameters and the five grain dehydration parameters.【Conclusion】 The current cultivars had different ear characters in HuangHuaiHai plain. These parameters contributed to grain dehydration rate, including the shorter bract, the lower moisture content of cob at physiological maturity, the larger ear angle, the fewer grain number per ear, and the smaller grain, which could be used in breeding and screening of mechanical grain harvest cultivars.
【Objective】 The objectives of this study were to investigate the variation of maize cob mechanical strength and its influence on kernel broken rate to provide a theoretical basis for improving maize harvest quality. 【Method】 Maize cultivars selection experiments were conducted in large area field. The same combine harvester and operating personnel were used in different harvest date to study the variation regularity and influence factors of maize cob mechanical strength during late growth period, to analyze the relationship between cob mechanical strength and kernel broken rate. The cob morphology, moisture content, dry matter accumulation, mechanical strength characters, kernel moisture content, and broken rate were investigated in this research. 【Result】 The results showed that, as harvest date delayed, maize kernel and cob moisture content decreased, and the bending strength of 8 cm and whole cob, and kernel broken rate showed a trend of decrease first and then increase. When kernel moisture content was below 20.1%, kernel broken rate increased exponentially with the increase in cob strength. When kernel moisture content was higher than 20.1%, kernel broken rate increased exponentially with the increase in bending strength of whole cob, and there was no significant relationship between kernel broken rate and bending strength of 8 cm cob. The bending strength was significantly and negatively correlated with moisture content of cob. In contrast, bending strength were significantly and positively correlated with penetration strength, dry weight, dry weight per unit length, and dry weight per unit volume. Path analysis showed that dry weight per unit length had the greatest effect on bending strength of cob. 【Conclusion】 Cob mechanical strength is one of the important factors affecting kernel broken rate in maize grain harvest. The dry matter accumulation and moisture content are important factors affecting the mechanical strength of the cob during late stage.
【Objective】 Nowadays, the higher grain moisture content at harvest limits the popularization and application of the mechanical grain harvesting technology. Maize grain filling process is accompanied by grain dehydration process after pollination, however, the relationship between these two processes remains a challenge. We used different maize cultivars to study the characters of the two processes and the relationships between them, which provided support for breeding and promotion of the harvesting technology. 【Method】 Field experiments were conducted in Xinxiang, Henan in 2015 and 2016. A total of 22 cultivars were studied and the controlled pollination was applied in every cultivar. In 2015, the sampling time was from the 26th day after pollination to November 14th. In 2016, the sampling time was from 11th day after pollination to October 17th. We measured dynamic changes of grain moisture content (MC), moisture (M), dry weight (DW) and fresh weight (FW) before and after physiological maturity to establish the relationships between these indexes and the accumulated temperature after pollination (T) by equations. Based on these equations, the grain dehydration process and the filling process were clarified. Then, we developed the relationship between these two processes by the correlation analysis. 【Result】 Results showed that T had the significant non-linear relationships with MC, M, DW and FW. Among them, the relationship between MC and T of 22 maize cultivars could be described by the Logistic Power regression model. The MC dropped to 28% when the T reached average 1 357°C·d, changing from 1 126 °C·d to 1 646 °C·d between cultivars. The average T was 1 480°C·d for 25% MC, changing from 1 218 °C·d to 1 810 °C·d. Dynamic change of MC could be divided into two stages based on the changes of DW and M. The first stage was from the start of grain growth to the end of linear filling process, in which the decreasing MC was mainly decided by the fast dry matter accumulation. The second stage followed the former ending to the harvest time, in which the decreasing MC was owned to the decreasing M. The correlation analysis showed that there was a significant negative correlation between the MC at physiological maturity and the filling days, and the T from pollination to physiological maturity in 2015 while the relationship was not significant in 2016. There was no significant relationship between the filling rate and the grain dehydration rate before physiological maturity, similar to the grain dehydration rate after physiological maturity and the total dehydration rate. 【Conclusion】 Our study found that the Logistic Power regression model had a good predictive stability to establish the relationship between MC and T. We proposed that MC was decided by the grain filling rate and the grain moisture loss rate respectively at different stages. Thus, breeders should not only pay attention to grain filling characters and maturity time, but also concern about the grain dehydration characters when evaluate suitable cultivars for the harvesting technology.
【Objective】 Yield and production efficiency are two equally important things under the condition of large-scale production. The sowing time and the harvesting time can be prolonged by various combinations of sowing date and different maturity cultivars, thus improving the utilization efficiency of combine machine and the maize production efficiency.【Method】 In this study, three maize cultivars, including KWS9384, Xinyu77 and M751, with different growth stages were selected to monitor the dynamic process of grain moisture content from 2015 to 2017. The predictive relationship model between the grain moisture content and the accumulated temperature (> 0°C) after pollination was established to analyze the key growth nodes of different combinations based on the local meteorological data.【Result】 The results showed that there were significant differences of grain yield and suitable sowing date between cultivars. The early maturity cultivar KWS9384 had a longer time of sowing and harvesting but a lower yield compared with the late maturity cultivars. The late maturity cultivars Xinyu77 and M751 both had higher yields but they needed more time to finish physiological maturity and to dry down grain to meet grain mechanical harvest. The combination plans of late maturity cultivar/early sowing or early maturity cultivar/late sowing could be used to coordinate the relationship between yield and grain moisture content, thus extending the sowing time and the grain harvesting time.【Conclusion】 This paper studied on the suitable sowing time and harvesting time of different maturity cultivars and gave the combination principle of cultivar and sowing date under the background of high yield and high efficiency production. The principle could maximize the utilization efficiency and benefit of combine machine under the specific ecology and production condition. This study provided the new information regarding the relevant researches and application of the maize grain mechanical harvesting technology.
