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The harvest moisture content (MC) of maize (Zea mays L.) is an important factor affecting industrial processing and harvest quality. However, higher MC levels may escalate drying expenses during production. While augmented plant density has shown potential to enhance maize yield, limited information exists regarding its impact on plant density and MC interaction. This study amassed four year of field trial data from four primary maize ecological areas in China (Longitude: 89°E to 125°E, Latitude: 35°N to 44°N) to examine the relationship between plant density and MC of maize. Our analysis revealed that increasing plant density exerted an effect on the MC of maize. This effect stemmed from a combination of uncertain grain development and premature plant senescence due to overcrowding. We categorized the relationship between plant density and MC into six types: NC-Type (No-changing), I-Type (ever-increasing), L-Type (ever-lessening), V-Type (like the valley), P-Type (like the peak), and W-Type (like a wave). On average, a variation approximately 0.053 % in MC was observed when the plant population changed by 1000 plants/ha. Moreover, different maize varieties contributed to a more substantial variation in MC. Despite the negligible impact of MC variation caused by plant density on grain quality, subsequent harvest management, and industrial production of maize, there was a significant enhancement in maize yield with increased plant density. Thus, increasing plant density presents an opportunity to boost maize output without compromising quality or grain moisture levels.

A high grain moisture content at harvest has been an important problem in the high latitude region of Northeast China, and it is closely related to the genotypes of varieties, local meteorological factors and planting management. However, delayed harvest at a low temperature could not effectively reduce the grain moisture content. In this study, we continuously observed the grain drying during the late stage of different maturing types of maize varieties in Daqing, Heilongjiang Province, China in 2016 and 2017. A two-segment linear model was used to analyze the different stages of the drying processes: 1) Two-segment linear model fitting can divide the grain drying process of all varieties into two separate linear drying processes with different slopes. 2) During the rapid drying stage, the drying was faster at a higher temperature. The rate of slow drying was influenced by air vapor pressure. 3) The moisture content and meteorological factors when the drying rate turns from one stage into the other were not consistent between varieties and years. After entering the frost period, temperatures below 0°C will significantly reduce the rate of grain drying. 4) Due to the short growth period of early-maturing varieties, the drying time was prolonged, and the grain moisture content was lower than that of the mid-late maturing varieties. Local meteorological conditions do not allow the drying of mid-late maturing varieties to achieve a lower moisture content. When the temperature falls below 0°C, the drying rate of grain decreases markedly. Therefore, one feasible way to solve the problem of high moisture content is to replace the early-maturing varieties and implement the corresponding cultivation techniques.

The rate of corn kernel breakage in the grain combine harvesters is a crucial factor affecting the quality of the grain shelled in the field. The objective of the present study was to determine the susceptibility of corn kernels to breakage based on the kernel moisture content in order to determine the moisture content that corresponds to the lowest rate of breakage. In addition, we evaluated the resistance to breakage of various corn cultivars. A total of 17 different corn cultivars were planted at two different sowing dates at the Beibuchang Experiment Station, Beijing and the Xinxiang Experiment Station (Henan Province) of the Chinese Academy of Agricultural Sciences. The corn kernel moisture content was systematically monitored and recorded over time, and the breakage rate was measured by using the grinding method. The results for all grain samples from the two experimental stations revealed that the breakage rate y is quadratic in moisture content x, y=0.0796x2−3.3929x+78.779; R2=0.2646, n=512. By fitting to the regression equation, a minimum corn kernel breakage rate of 42.62% was obtained, corresponding to a corn kernel moisture content of 21.31%. Furthermore, in the 90% confidence interval, the corn kernel moisture ranging from 19.7 to 22.3% led to the lowest kernel breakage rate, which was consistent with the corn kernel moisture content allowing the lowest breakage rate of corn kernels shelled in the field with combine grain harvesters. Using the lowest breakage rate as the critical point, the correlation between breakage rate and moisture content was significantly negative for low moisture content but positive for high moisture content. The slope and correlation coefficient of the linear regression equation indicated that high moisture content led to greater sensitivity and correlation between grain breakage and moisture content. At the Beibuchang Experiment Station, the corn cultivars resistant to breakage were Zhengdan 958 (ZD958) and Fengken 139 (FK139), and the corn cultivars non-resistant to breakage were Lianchuang 825 (LC825), Jidan 66 (JD66), Lidan 295 (LD295), and Jingnongke 728 (JNK728). At the Xinxiang Experiment Station, the corn cultivars resistant to breakage were HT1, ZD958 and FK139, and the corn cultivars non-resistant to breakage were ZY8911, DK653 and JNK728. Thus, the breakage classifications of the six corn cultivars were consistent between the two experimental stations. In conclusion, the results suggested that the high stability of the grinding method allowed it to be used to determine the corn kernel breakage rates of different corn cultivars as a function of moisture content, thus facilitating the breeding and screening of breakage-resistant corn.

Understanding the water status of specific organs can be helpful in evaluating the life activities and growth conditions of maize. To accurately judge organ growth conditions and thus design appropriate interventions, it is necessary to clarify the true water dynamics of each maize organ. Using multiple maize cultivars with different growth periods, spatio-temporal water dynamics were analyzed here in the leaves, stalks, and ear components. Leaf water content was found to gradually decrease from both the bottom and top of the plant to the middle, whereas stalk water content decreased sequentially from the top to the bottom. Each successively higher node from the bottom of the plant was associated with decreases of 0.99% and 1.27% water content in the leaves and stalks, respectively. The water dynamics in leaves and internodes showed three clear stages: the slow loss, rapid loss, and balance stage. A water content of 60% appeared to be an irreversible turning point for initiation of senescence. Using normalized growth period as a measure, each of the tested cultivars could be assigned into one of two types based on their water dynamics: stay-water or general type. General-type cultivars had a shorter duration with a high water content and a water loss rate approximately twice as high as that of the stay-water type. This may have been related to the leaf senescence characteristics. However, the stay-water trait did not interfere with water dynamics of the ear components. Therefore, it may not be robust to evaluate the kernel dehydration of maize according to leaf senescence conditions due to the weak correlation between kernel water content and leaf senescence characteristics.

Nitrogen fertilizer application is an important measure to obtain high and stable corn yield, and the moisture content of corn grains is an important factor affecting the quality of mechanical grain harvesting. In this study, four different nitrogen fertilizer treatments from 0 to 450 kg ha–1 pure nitrogen were set for a planting density of 12.0×104 plants ha–1 in 2017 and 2018, and 18 different nitrogen fertilizer treatments from 0 to 765 kg ha–1 pure nitrogen were set for planting densities of 7.5×104 and 12.0×104 plants ha–1 in 2019, to investigate the effect of nitrogen application rate on the moisture content of corn grains. Under each treatment, the growth of corn, leaf area index (LAI) of green leaves, grain moisture content, and grain dehydration rate were measured. The results showed that, as nitrogen application increased from 0 to 765 kg ha–1, the silking stage was delayed by about 1 day, the maturity stage was delayed by about 1–2 days, and the number of physiologically mature green leaves and LAI increased. At and after physiological maturity, the extreme difference in grain moisture content between different nitrogen application rates was 1.9–4.0%. As the amount of nitrogen application increased, the corn grain dehydration rate after physiological maturity decreased, but it did not reach statistical significance between nitrogen application rate and grain dehydration rate. No significant correlation was observed between LAI at physiological maturity and grain dehydration rate after physiological maturity. In short, nitrogen application affected the grain moisture content of corn at and after physiological maturity, however, the difference in grain moisture content among different nitrogen application rates was small. These results suggest that the effect of nitrogen application on the moisture content of corn grains should not be considered in agricultural production.

The harvest method of shelling corn (Zea mays L.) kernels in the field decreases labor costs associated with transporting, drying and threshing the crop. However, it was previously found that the kernel moisture content increased after field harvest, which decreased the value of corn kernels. To identify the reasons underlying the increase, we conducted a multiyear and -area trial in the Huang-Huai-Hai Plain, China and performed a staged-harvest test at several phases of kernel dry-down. The test investigated a range of parameters such as the kernel moisture content pre- and post-harvest, the kernel breakage rate, the amount of impurities, and the moisture content of various other plant tissues. An analysis of 411 pairs of pre- and post-harvest samples found that kernel moisture content after harvest was 2.2% higher than that before harvest. In the staged-harvest test, however, a significant increase was only observed when the kernel moisture content before harvest was higher than 23.9%. The increase in post-harvest kernel moisture content was positively associated with the pre-harvest kernel moisture content, breakage rate and impurity rate. Typically, at harvest time in this region, there is a significant fraction of immature crops with a high moisture content, resulting in kernels that are prone to breakage or impurities that ultimately lead to increases in water content after harvest. Therefore, we suggest using hybrids that quickly wither late in the growing stage. Additionally, farmers should delay harvest in order to minimize the pre-harvest kernel moisture content and thus reduce breakages and impurities, thereby improving the quality of kernels after harvest and the efficiency of corn kernel farming in China.

The uneven distribution of solar radiation is one of the main reasons for the variations in the yield gap between different regions in China and other countries of the world. In this study, different solar radiation levels were created by shading and the yield gaps induced by those levels were analyzed by measuring the aboveground and underground growth of maize. The experiments were conducted in Qitai, Xinjiang, China, in 2018 and 2019. The maize cultivars Xianyu 335 (XY335) and Zhengdan 958 (ZD958) were used with planting density of 12×104 plants ha–1 under either high solar radiation (HSR) or low solar radiation (LSR, 70% of HSR). The results showed that variation in the solar radiation resulted in a yield gap and different cultivars behaved differently. The yield gaps of XY335 and ZD958 were 8.9 and 5.8 t ha–1 induced by the decreased total intercepted photosynthetically active radiation (TIPAR) of 323.1 and 403.9 MJ m-2 from emergence to the maturity stage, respectively. The average yield of XY335 was higher than that of ZD958 under HSR, while the average yield of ZD958 was higher than that of XY335 under LSR. The light intercepted by the canopy and the photosynthetic rates both decreased with decreasing solar radiation. The aboveground dry matter decreased by 11.1% at silking and 21% at maturity, and the dry matter of vegetative organs and reproductive organs decreased by 9.8 and 20.9% at silking and by 12.1 and 25.5% at physiological maturity, respectively. Compared to the HSR, the root weights of XY335 and ZD958 decreased by 54.6 and 45.5%, respectively, in the 0–60 cm soil layer under LSR at silking stage. The aboveground and underground growth responses to different solar radiation levels explained the difference in yield gap. Selecting suitable cultivars can increase maize yield and reduce the yield gaps induced by variation of the solar radiation levels in different regions or under climate change.

Yield gap exists because the current attained actual grain yield cannot yet achieve the estimated yield potential. Chinese high yield maize belt has a wide span from east to west which results in different solar radiations between different regions and thus different grain yields. We used multi-site experimental data, surveyed farmer yield data, the highest recorded yield data in the literatures, and simulations with Hybrid-Maize Model to assess the yield gap and tried to reduce the yield gap by matching the solar radiation and plant density. The maize belt was divided into five regions from east to west according to distribution of accumulated solar radiation. The results showed that there were more than 5.8 Mg ha–1 yield gaps between surveyed farmer yield and the yield potential in different regions of China from east to west, which just achieved less than 65% of the yield potential. By analyzing the multi-site density experimental data, we found that the accumulated solar radiation was significantly correlated to optimum plant density which is the density with the highest yield in the multi-site density experiment (y=0.09895×–32.49, P

The most significant problem of maize grain mechanical harvesting quality in China at present is the high grain breakage rate (BR). BR is often the key characteristic that is measured to select hybrids desirable for mechanical grain harvesting. However, conventional BR evaluation and measurement methods have challenges and limitations. Microstructural crack parameters evaluation of maize kernel is of great importance to BR. In this connection, X-ray computed microtomography (μ-CT) has proven to be a quite useful method for the assessment of microstructure, as it provides important microstructural parameters, such as object volume, surface, surface/volume ratio, number of closed pores, and others. X-ray computed microtomography is a non-destructive technique that enables the reuse of samples already measured and also yields bidimensional (2D) cross-sectional images of the sample as well as volume rendering. In this paper, six different maize hybrid genotypes are used as materials, and the BR of the maize kernels of each variety is tested in the field mechanical grain harvesting, and the BR is used as an index for evaluating the breakage resistance of the variety. The crack characteristic parameters of kernel were detected by X-ray micro-computed tomography, and the relationship between the BR and the kernel crack characteristics was analyzed by stepwise regression analysis. Establishing a relationship between crack characteristic parameters and BR of maize is vital for judging breakage resistance. The results of stepwise multiple linear regression (MLR) showed that the crack characteristics of the object surface, number of closed pores, surface of closed pores, and closed porosity percent were significantly correlated to the BR of field mechanical grain harvesting, with the standard partial regression coefficients of −0.998, −0.988, −0.999, and −0.998, respectively. The R2 of this model was 0.999. Results validation showed that the Stepwise MLR Model could well predict the BR of maize based on these four variables.

The accurate evaluation of maize stalk lodging resistance in different growth periods enables timely management of lodging risks and ensures stable and high maize yields. Here, we established five different sowing dates to create different conditions for maize growth. We evaluated the effects of the different growth conditions on lodging resistance by determining stalk morphology, moisture content, mechanical strength and dry matter, and the relationship between stalk breaking force and these indicators during the silking stage (R1), milk stage (R3), physiological maturity stage (R6), and 20 days after R6. Plant height at R1 positively affected stalk breaking force. At R3, the coefficient of ear height and the dry weight per unit length of basal internodes were key indicators of stalk lodging resistance. At R6, the key indicators were the coefficient of the center of gravity height and plant fresh weight. After R6, the key indicator was the coefficient of the center of gravity height. The crushing strength of the fourth internode correlated significantly and positively with the stalk breaking force from R1 to R6, which indicates that crushing strength is a reliable indicator of stalk mechanical strength. These results suggest that high stalk strength and low ear height benefit lodging resistance prior to R6. During and after R6, the coefficient of the center of gravity height and the mechanical strength of basal internodes can be used to evaluate plant lodging resistance and the appropriate time for harvesting in fields with a high lodging risk.

Intraspecific competition is a common phenomenon in agricultural production, and maize is one of the most sensitive grass species to intraspecific competition due to its low tillering ability. This study evaluated and analyzed intraspecific competition in maize, and screened competitive indices that could be used to evaluate intraspecific competition in a maize population. A 2-year field experiment was conducted using the maize hybrid Zhongdan 2 at 12 plant densities ranging from 1.5 to 18.0 plants (pl) m−2. The results showed that the response of single-plant grain yield and dry matter at harvest to increased plant density decreased exponentially and that the harvest index decreased linearly. The response of population-level grain yield to plant density was curvilinear, producing a maximum value at the optimum population density. However, the yielddensity equation agreed well with the Steinhart-Hart equation curves, but not with the quadratic equation curves reported by most previous studies. Competitive indices are used to evaluate competition in a plant population or plant species. The present results show that competitive intensity (CI) and absolute severity of competition (ASC) increased with increasing plant density; however, relative yield (RY) and relative reproductive efficiency (RReff) decreased. The different responses of these indices reflect different aspects of competition. According to the analysis of CI, ASC, RY, and RReff, higher CI and ASC values indicate higher intraspecific competition, whereas higher RY and RReff values indirectly reflect lower intraspecific competition. These competitive indices evaluate not only the intraspecific competitive intensity under different plant densities of the same cultivar but also those of different cultivars under the same plant density. However, some overlap exists in the calculations of ASC, CI, and RY, so one could simply select any one of these indices to evaluate intraspecific competition in a maize population. In conclusion, the present study provides a method to evaluate intraspecific competition in maize populations, which may be beneficial for breeding high-yield maize varieties in the future.

Increasing plant density is an effective way to enhance maize yield, but often increases lodging rate and severity, significantly elevating the risk and cost of maize production. Therefore, lodging is a major factor restricting future increases in maize yield through high-density planting. This paper reviewed previous research on the relationships between maize lodging rate and plant morphology, mechanical strength of stalks, anatomical and biochemical characteristics of stalks, root characteristics, damage from pests and diseases, environmental factors, and genomic characteristics. The effects of planting density on these factors and explored possible ways to improve lodging resistance were also analyzed in this paper. The results provide a basis for future research on increasing maize lodging resistance under high-density planting conditions and can be used to develop maize cultivation practices and lodging-resistant maize cultivars.

Competition is a common phenomenon in agriculture production. Research on the relationship between competitive ability and crop yield is extensive, but the results have been inconsistent. Few studies have focused on the relationship between population competitive intensity and yield of maize (Zea mays L.) cultivars. The main objective of this study was to determine if a consistent relationship exists between maize yield and competitive ability. A two-year field experiment was conducted, employing a de Wit replacement series design. When two maize cultivars were grown in a mixture, yield was reduced for the modern cultivar and increased for the older cultivar. In each replacement series, per plant level yield of each cultivar, and population level yield of the mixture, decreased with increasing proportion of the older cultivar. Competitive ratio (CR) reflected differences in competitive ability of the three maize cultivars. In each replacement series, population competition pressure (PCP) increased with increasing proportion of the older cultivar, indicating that the older cultivar was a strong competitor. Biomass yield, grain yield, harvest index, thousand-kernel weight, and kernel number per plant, were negatively correlated with PCP. Our results demonstrated that inter-cultivar competition affects maize productivity, and increasing PCP will decrease translocation of assimilates to grain and, ultimately, reduce yield. Therefore, there is a negative correlation between population competitive intensity and yield performance in maize, breeders should develop a communal ideotype that would not perform well in competition in future.

In 2010, Chinese maize yields increased from 961.5 kg ha−1 in 1949 to 5 453.8 kg ha−1. This increase is the result of genetic improvements, an increase in nitrogen application, and refinement of planting densities. The objective of this study was to provide a theoretical basis for maize production research by analyzing the maize yield gain characteristics. 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 the 1950s and continuing through each decade into the 2000s. The selections and their corresponding decade were as follows: Baihe, 1950s; Jidan 101, 1960s; Zhongdan 2, 1970s; Yedan 13, 1980s; Zhengdan 958, 1990s; and Xianyu 335, 2000s. Each variety was planted under four different densities (37 500, 52 500, 67 500, and 82 500 plants ha−1) and four different nitrogen applications (0, 150, 225, and 300 kg ha−1) to study the effects on yield gain characteristics. The obtained results demonstrated that there was a maize yield increase of 123.19% between the 1950s variety and the 2000s variety. 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 at 67 500 plants ha−1 with 225 kg ha−1 nitrogen application), the contribution types and corresponding yield increase percentages were as follows: genetic improvement, 45.37%; agronomic-management improvement, 30.94%; and genotype× agronomic-management interaction, 23.69%. At high-yielding cultivation levels (planting at 82 500 plants ha−1 with 300 kg ha−1 nitrogen application), the contribution types and corresponding yield increase percentages were as follows: genetic improvement, 31.30%; agronomic-management improvement, 36.23%; and genotype × agronomic-management interaction, 32.47%. The contribution of agronomic-management and genotype × 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.

Experiment was conducted at the Gongzhuling Experimental Station of Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Jilin Province, China, during 2009–2010. Six representative varieties of maize (Baihe in the 1950s, Jidan 101 in the 1960s, Zhongdan 2 in the 1970s, Yedan 13 in the 1980s, Zhengdan 958 in the 1990s, and Xianyu 335 in the 2000s) were each planted under two different densities (52 500 and 82 500 plants ha−1) and two different nitrogen application levels (150 and 300 kg ha−1). Root characteristics and distribution among soil layers were studied by the field root digging method. The results showed that root mass increased with the process of the growth and development of the plant, and it peaked at kernel filling stage, and decreased at maturity due to the root senesces. Root mass of different maize varieties from the 1950s to 1980s had a trend of increase, while it decreased for the modern varieties. Root length and root surface areas had the similar changing trend. The study suggested that early maize varieties may have root redundancy, and reducing root redundancy may be a direction for variety improvement for high yield. Root characteristics were affected by nitrogen application level and density; modern varieties were more suitable for higher fertilizer application level and density conditions. Root characteristics distribution among soil layers decreased by an exponent equation, but the regression coefficients of different varieties were different. Though the root length density (RLD) of every soil layer of different varieties also decreased by an exponent equation, there were large variations of RLD in every part of a layer.