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In maize (Zea mays L.), rational root structure promotes high grain yield under dense sowing conditions. This study was conducted at Qitai Farm in Xinjiang, China, in 2019 and 2021. A traditional wide and narrow row planting method was adopted, with wide rows of 0.7 m and narrow rows of 0.4 m. The cultivars DH618 and SC704, which have grain yield potentials of 22.5 and 15 Mg ha−1, respectively, were selected for study of the root structure and distribution characteristics under high-yield and high-density planting conditions. The highest yield (20.24 Mg ha−1) was achieved by DH618 under a planting density of 12 × 104 plants ha−1. The root structure of DH618 was well developed at that planting density, and the root dry weight (RDW) was 17.49 g plant−1 and 14.65 g plant−1 at the silking and maturity stages, respectively; these values were 7.56% and 11.86% higher, respectively, than those of SC704. At the silking stage, the proportions of RDW at soil depths of 0–10, 10–20, 20–40, and 40–60 cm were 66.29%, 11.83%, 16.51%, and 5.38%, respectively, for DH618; over the 20–60 cm soil layer, this was an average of 4.04% higher than the RDW of SC704. At maturity, the proportions of RDW at soil depths of 0–10, 10–20, 20–40, and 40–60 cm were 61.40%, 11.19%, 17.19%, and 10.21%, respectively, for DH618, which was an average of 9.59% higher than that of SC704 over the 20–60 cm soil layer. At maturity, DH618 roots were mainly distributed in the narrow rows, accounting for 72.03% of the root structure; this was 9.53% higher than the roots of SC704. At silking and maturity, the root weight densities of DH618 were 471.98 g m−3 and 382.98 g m−3, respectively (5.18% and 5.97% higher, respectively, than the root weight densities of SC704). The root lengths of DH618 were 239.72 m plant−1 and 199.04 m plant−1 at the silking and maturity stages, respectively; these were 16.45% and 25.39% higher, respectively, than the root lengths of SC704. The root length densities were 0.58 cm cm−3 and 0.46 cm cm−3 at the silking and maturity stages, respectively, and these were 16.86% and 17.08% higher, respectively, than the root length densities of SC704. This study indicated that the maize hybrid DH618 had a more developed root structure with increased root distribution in the deep soil and narrow rows under high-density planting compared to cultivar SC704, contributing to high grain yield under dense planting. [ABSTRACT FROM AUTHOR]

A quantitative understanding of the factors driving changes in grain filling is essential for effective prioritization of increasing maize yield. Grain filling is a significant stage in maize yield formation. Solar radiation is the energy source for grain filling, which is the ultimate driving factor for final grain weight and grain filling capacity that determine maize yield. Here, we first confirmed the quantitative relationships between grain filling parameters and photosynthetically active radiation (PAR) by conducting field experiments using different shading and plant density conditions and cultivars in 2019 and 2020 in Xinjiang, China. The results showed that with every 100 MJ m−2 increase in PAR, the average grain filling rate (G ave), maximum grain-filling rate (G max), and the kernel weight at the time of maximum grain-filling rate (W max) increased by 0.073 mg kernel−1 day−1, 0.23 mg kernel−1 day−1, and 0.24 mg kernel−1, and the time of maximum grain-filling rate (T max) delayed by 0.91 day. Relative changes in PAR were significantly and positively correlated with relative changes in yield and G ave. With every 1% change in PAR, yield and G ave changed by 1.16 and 0.17%, respectively. From the perspective of grain filling capacity, DH618 was a more shade-resistant cultivar than XY335 and ZD958. It is urgent to breed maize cultivars with low light tolerance and high grain yield in the face of climate change, particularly the decrease in solar radiation. [ABSTRACT FROM AUTHOR]

Improved canopy structure was instrumental in setting maize yield records, and yet it has rarely been examined in China. At Qitai Farm in Xinjiang, we conducted a 4‐year field experiment using China's six highest‐yielding maize hybrids sorted into three yield level groups that were grown at similar growth durations and at optimum densities. The average yield of high‐yield level (HL, 22.3 Mg ha−1) was 7.2% and 24.6% higher than that of medium‐yield level (ML) and low‐yield level (LL), respectively. For each yield level, we measured morphological traits that influence canopy structure and yield. They included plant height, ear height, ear ratio, internode length, leaf numbers, leaf angle, LOV, leaf area, and spatial density of leaf area. Among the preceding morphological traits of the three yield levels, HL's best optimized the canopy structure, as shown by improved light distribution (19.0% light transmission at the ear) and increased light interception per unit leaf area per day (LIPA, 51.7 MJ m−2 day−1) in the canopy. In comparison, light transmission was 12.2% and 15.9% at the ear and the total LIPAs were 37.2 and 29.0 MJ m−2 day−1 at silking for ML and LL, respectively. HL had significantly longer leaf area duration and a higher photosynthetic rate, especially at the grain filling stage, and its total accumulated biomass at maturity was significantly better (by 13.9%) than LL's. HL's harvest index (0.54) was significantly higher than that of ML (0.52) and LL (0.48). HL's radiation and heat use efficiencies were 2.61% and 1.37 g °C−1 day−1 m−2, both significantly greater than those of ML and LL. Therefore, optimum maize plant types can significantly improve canopy structure and increase resource use efficiency and grain yield. [ABSTRACT FROM AUTHOR]

Solar radiation is the energy source for crop growth, as well as for the processes of accumulation, distribution, and transfer of photosynthetic products that determine maize yield. Therefore, learning the effects of different solar radiation amounts on maize growth is especially important. The present study focused on the quantitative relationships between solar radiation amounts and dry matter accumulations and transfers in maize. Over two continuous years (2017 and 2018) of field experiments, maize hybrids XY335 and ZD958 were grown at densities of 4.5 × 104 (D1), 7.5 × 104 (D2), 9 × 104 (D3), 10.5 × 104 (D4), and 12 × 104 (D5) plants/ha at Qitai Farm (89°34′E, 44°12′N), Xinjiang, China. Shading levels were 15% (S1), 30% (S2), and 50% (S3) of natural light and no shading (CK). The results showed that the yields of the commonly planted cultivars XY335 and ZD958 at S1, S2, and S3 (increasing shade treatments) were 7.3, 21.2, and 57.6% and 11.7, 31.0, and 61.8% lower than the control yields, respectively. Also, vegetative organ dry matter translocation (DMT) and its contribution to grain increased as shading levels increased under different densities. The dry matter assimilation amount after silking (AADMAS) increased as solar radiation and planting density increased. When solar radiation was <580.9 and 663.6 MJ/m2, for XY335 and ZD958, respectively, the increase in the AADMAS was primarily related to solar radiation amounts; and when solar radiation was higher than those amounts for those hybrids, an increase in the AADMAS was primarily related to planting density. Photosynthate accumulation is a key determinant of maize yield, and the contributions of the vegetative organs to the grain did not compensate for the reduced yield caused by insufficient light. Between the two cultivars, XY335 showed a better resistance to weak light than ZD958 did. To help guarantee a high maize yield under weak light conditions, it is imperative to select cultivars that have great stay-green and photosynthetic efficiency characteristics. [ABSTRACT FROM AUTHOR]

Understanding the contribution of aboveground dry matter (DM) production and harvest index (HI) to maize grain yield is essential to further improve grain yield to ensure future food growing requirements. In this study, we collected 548 sets of data of DM, HI, and grain yield from a multisite (40 sites) and multiyear (2009–2016) experiment conducted in major maize‐growing regions across China and 615 sets of data from 40 published papers distributed from 1988 to 2018 to assess the performance of DM, HI, and their contributions to grain yield. It was found that the average contribution rate of DM was 73.71%, which was much higher than those of HI (26.28%) across China. For the five different modern hybrids, the contribution rates of DM to grain yield (ranged from 71.36% to 89.10%) were also significantly higher than those of HI (ranged from 10.79% to 28.64%) on a large spatial scale. The significant differences in grain yields between cultivars were mainly due to the differences in HI. Among the four maize‐growing regions, the contribution rates of DM in both NW (57.34%) and NM (64.46%) were higher than those of HI (42.66% and 35.54%, respectively). In contrast, the contribution rates of HI in HM (52.67%) and SW (50.92%) were slightly higher than those of DM (47.33% and 49.08%, respectively). The interregional differences in grain yield were mainly attributed to the differences in DM between regions. Additionally, combining the data of this study and data collected from previous studies, we found that the increase in maize grain yield under lower yield levels (<15 Mg/ha) was mainly attributed to the increase in both DM and HI, while that under higher yield levels (>15 Mg/ha) was mainly dependent on the increase in DM. [ABSTRACT FROM AUTHOR]

• The LAI was 6.74 at silking, which was 3.35 at maturity for high yield level. • Pre-silking dry matter plateaued at 13.49 Mg ha-1 when grain yield ≥ 17 Mg ha-1. • The proportion of post-silking dry matter was about 70% at yield level of 25.0 Mg ha-1. • HI can be further increased from 0.52 to 0.55 by erect type cultivars and precise field regulation. • Longer post-silking duration and lower dry matter transfer rate are vital for high yield. Feeding a growing population requires improving crop yield without compromising the environment. Maize (Zea mays L.) is the largest food crop in the world. Identifying underlying drivers that increase maize yield is not only important for food security but also high resources use efficiency and environmental sustainability. Dry matter (DM) accumulation and its allocation to kernels are key factors that determine the final maize grain yield. To clarify the characteristics of DM accumulation, and allocation for maize yield breakthrough, data from previous publications from the 1970s to 2020s were collected and analyzed in combination with data from five years' field experiment conducted with six maize cultivars once yielding the highest in China and in all previous publications globally. As grain yield increased from 1.0 to 25.0 Mg ha−1, a longer growth duration was essential, especially post-silking duration. A large but not excessive maximum leaf area index (LAI, 6.74) at silking was needed for crowded populations, and a relatively large LAI (3.35) at maturity was necessary. The pre-silking DM plateaued at 13.49 Mg ha−1 when grain yield exceeded 17.0 Mg ha−1. The proportion of post-silking DM to total DM increased with yield and was about 70% when the yield level was 25.0 Mg ha−1. By contrast, the DM transfer rate decreased with increasing yield. In addition, the harvest index (HI) could be further increased from a steady 0.52 to 0.55 when grain yield exceeded 10.1 Mg ha−1. These innovative findings are of great significance for yield breakthrough and high resources use efficiency. [Display omitted] [ABSTRACT FROM AUTHOR]

The root system connects the plant with the soil, which is a key factor in determining the utilization of soil resources and plant growth potential. Solar radiation can change maize shoot and root growth and affect grain formation. In this study, the effects of different solar radiation conditions on root morphology of three maize cultivars XY335, ZD958 and DH618 and their quantitative relationships were studied by conducting shading experiments. This study was conducted in maize high yield region of Qitai and Yinchuan, China, in 2018 and 2019. The planting densities were 7.5 × 104 (D1) and 12 × 104 (D2) plants ha−1. The shading levels were natural light (CK), shading 15% (S1), 30% (S2) and 50% (S3). The results showed that maize responded to the decreased solar radiation through the increase in ratio of shoot dry weight (SWR) to whole plant dry weight and the decrease in ratio of root dry weight (RWR) to whole plant dry weight. As the solar radiation decreased, the root length density (RLD), root surface area (RSA), average root diameter (ARD) and root length ratio (RLR) decreased, while the specific root length (SRL) increased. With 100 MJ m−2 decrease in solar radiation, the RWR, RLD, RSA and RLR each decreased by 1.47%, 0.5 mm cm−3,0.4 m m−2 and 0. 19 m g−1, respectively. Among the cultivars, the changes of DH618 were the fastest followed by XY335 and ZD958 but DH618 maintained the largest root system under any solar radiation condition. After the decrease of solar radiation, RWR, RLD and RLR were significantly positively correlated with the yield. This indicated that large root systems were conducive to the rapid response to decreased solar radiation and important for achieving stable and high yield. Maize cultivars with these type of root systems should be recommended to better adapt low solar radiation induced by regional variation or climate change. [ABSTRACT FROM AUTHOR]

• Maize is the most widespread crop under various solar radiation conditions. • Lodging adversely affects maize yields, especially under low solar radiation conditions. • Quantitative relationships exist between solar radiation and indexes of maize stalk lodging mechanical resistance. • Different maize genotypes exhibit different lodging risks in response to different solar radiation levels. Lodging adversely affects maize (Zea mays L.) yields and quality, especially under low sunlight conditions. Here, we investigated the effects of different levels of solar radiation on maize lodging. To study the quantitative effects of different solar radiation on the lodging resistant mechanism of maize stalks, we chose two maize cultivars, Xianyu 335 (XY335) and Zhengdan 958 (ZD958), and grew them in two regions that receive the most abundant solar radiation in Xinjiang and Ningxia China in 2018 and 2019. Maize plants were exposed to different shade levels (15 % (S1), 30 % (S2), 50 % (S3), and natural light as the control (CK)) and different planting densities (4.5 × 104 (D1), 7.5 × 104 (D2), 9 × 104 (D3), 10.5 × 104 (D4), and 12 × 104 (D5) plants ha− 1) to create different solar radiation conditions. The results showed that lodging percentage was significantly negatively correlated with the stalk bending strength (SBS), rind penetration strength (RPS), vertical root pulling resistance (VRPR), dry weight per unit length (DWUL), the cellulose and lignin content and grain yield which significantly decreased with decreasing total intercepted photosynthetically active radiation (TIPAR). Quantitative analysis showed that for every 1 MJ m- 2 reduction in TIPAR, the SBS and RPS decreased by 0.0667 N and 0.075 N, DWUL and the content of cellulose and lignin of maize stalk significantly decreased with decreasing TIPAR, by 0.88 mg cm− 1, 0.3 mg g- 1 and 0.06 mg g− 1, respectively. Lodging percentage was significantly negatively correlated with TIPAR, the lodging percentage increased by 0.17 % with a decrease in TIPAR of 1 MJ m- 2. Comparison of cultivars revealed that the rate of decrease in SBS, RPS, VRPR, DWUL and the cellulose and lignin content were greater for XY335 than for ZD958, indicating that the stalk strength of XY335 was more sensitive than ZD958 to decreasing levels of TIPAR. However, SBS, RPS, DWUL and the cellulose and lignin content of XY335 were higher than ZD938 and the lodging percentage of XY335 was lower than ZD958 which meant that XY335 had a stronger stalk strength to resistance to lodging. This is important for understanding lodging resistance and developing cultivars suited to different solar radiation conditions in different regions, as well as to changing solar radiation conditions induced by global climate change. [ABSTRACT FROM AUTHOR]

The final leaf number is an important morphological characteristic of maize (Zea mays L.) and is therefore an important input parameter in some maize crop models. In this study, field experiments were conducted from 2013 to 2016 at 23 sites across China, which were located between latitudes of 26°30′ and 46°45′ N, focusing on five modern maize cultivars, in order to determine the amplitude of variation in mean leaf numbers between each cultivar, identify differences between the mean leaf numbers of cultivars under different climatic conditions, and clarify the effects of the differences in final leaf numbers on aboveground dry matter (DM) and grain yield. The results showed that the mean final leaf numbers increased in the order of XY335 < NH101 < ZD909 < ZD958 < DH11 among the five cultivars, with the wide distribution ranges of final leaf numbers being 17.0–23.3 (DH11), 16.7–22.3 (ZD958), 16.7–22.0 (ZD909), 16.7–22.3 (NH101), and 17.0–22.0 (XY335) across all locations. In addition, leaf numbers above and below the primary ear showed the same trends with the mean final leaf numbers for the same cultivars. Many climatic factors were found to significantly affect the final leaf numbers across four maize-growing regions in China, and the result of stepwise regression indicated that the influences of photoperiod and temperature, in particular, were greater than other climatic factors for these cultivars. Finally, there were found to be significant and positive relationships between the final leaf number and (1) the maximum leaf area index (LAImax), (2) DM at both silking and physiological maturity, and (3) grain yield for the same cultivars across all locations. The results of this study are of great importance for guiding future trans-regional maize cultivation and further model calibration. [ABSTRACT FROM AUTHOR]

Increasing planting density is an important practice associated with increases in maize yield, but densely planted maize can suffer from poor light conditions. In our two-year field experiments, two morphologically different cultivars, ZD958 (less compact) and DH618 (more compact), were planted at 120,000 plants ha−1 and 135,000 plants ha−1, respectively. We established different leaf area index (LAI) treatments by removing leaves three days after silking: (1) control, no leaves removed (D0); (2) the two uppermost leaves removed (D1); (3) the four uppermost leaves removed (D2); (4) the leaves below the third leaf below the ear removed (D3); (5) the leaves of D1 and D3 removed (D4); (6) the leaves of D2 and D3 removed (D5). Optimal leaf removal improved light distribution, increased photosynthetic capacity and the post-silking source-sink ratio, and thus the grain yield, with an average LAI of 5.9 (5.6 and 6.2 for ZD958 and DH618, respectively) for the highest yields in each year. Therefore, less-compact cultivars should have smaller or fewer topmost leaves or leaves below the ear that quickly senesce post-silking, so as to decrease leaf area and thus improve light distribution and photosynthetic capacity in the canopy under dense planting conditions. However, for more compact cultivars, leaves below the ear should senesce quickly after silking to reduce leaf respiration and improve the photosynthetic capacity of the remaining top residual leaves. In future maize cultivation, compact cultivars with optimal post-silking LAI should be adopted when planting densely. [ABSTRACT FROM AUTHOR]

Coordination between source and sink is vital for the final maize grain yield planted under high density. To clarify the source and sink characteristics of high yield potential (22.5 Mg ha-1), a four-year field experiment was conducted at Qitai Farm in Xinjiang, China. At silking, the maximum leaf area indexes were 5.8, 7.5, and 6.2 for cultivars of high yield level-1 (H1), high yield level-2 (H2), and high yield level-3 (H3) with yield increase of H1 < H2 < H3, which were 2.2, 4.6, and 3.9 at maturity, respectively. The H3 biomass was significantly higher than those of H1 and H2 during post-silking, and the H2 and H3 total kernel numbers were significantly higher than H1's, although H2 had a significantly higher harvest ear number. While H3's kernel size was not the largest of the three levels, H3 had a significantly higher thousand kernel weight. The grain filling analysis showed that H1 and H3 had shorter lag period durations (D1) than H2, and H3 had a longer maturation drying period duration (D3) than the other groups did. However, H1 and H3 had significantly higher grain filling rates than H2 in the lag period (D1), and H3's was the lowest in the maturation drying period (D3). Also, H3's maximum grain filling rate was significantly higher than H2's, and H3 had significantly higher biomass/kernel number and kernel weight/leaf area ratios than H1 and H2 did. Based on our findings, three high yield levels were classified into three source-sink types: (1) H1: small source and weak productivity, small sink and short maturation drying period duration (D3); (2) H2: large source but weak productivity, large sink but slow grain filling start, and low maximum grain filling rate; (3) H3: small source but strong productivity, large sink, fast grain filling start, long maturation drying period duration (D3), and high maximum grain filling rate. We achieved an actual high yield of 22.4 Mg ha-1 for H3, which was also the highest yield in China. Therefore, hybrids with H3-type source and sink characteristics should be selected in the future for high-yield cultivation under dense planting. • Maize yield level of more than 22.5 Mg ha-1 has small source and strong biomass productivity under high density. • Large sink with more population kernel number and higher thousand kernel weight are vital for high yield maize. • Fast grain filling start, higher maximum grain filling rate and longer maturation drying period duration are essential. [ABSTRACT FROM AUTHOR]

• The maize height morphological traits showed wide variations across China. • The mean internode length mainly contributed to the variation in plant height. • The mean internode length below the ear resulted in the variation in ear height. • Photoperiod and minimum temperature mainly affected the maize plant and ear height. • The maize plant height significantly affected aboveground dry matter and grain yield. Maize (Zea mays L.) height morphological traits (i.e., plant height, ear height, and ear ratio) are important parts of maize plant type structure and have played an important role in the improvement of maize lodging resistance and historical increases in grain yield. In this study, field experiments were conducted from 2013 to 2016 at 23 sites in China between 26°30′–46°45′ N latitude and 81°19′–130°16′ E longitude. Five common cultivars and one planting density (6.0 × 104 plants ha−1) were used to determine the amplitude of variation in maize height morphological traits for the same cultivars and the differences in maize height morphological traits between different cultivars. The results elucidated that the main factors affecting maize height morphological traits and characterize the responses of aboveground dry matter (DM) and grain yield to differences in plant height over a wide range of environmental conditions. The findings showed that for cultivars Denghai 11 (DH11), Nonghua 101 (NH101), Xianyu 335 (XY335), Zhengdan 958 (ZD958), and Zhongdan 909 (ZD909), plant heights ranged from 233.1 to 395.3, 240.7–389.6, 246.0–370.0, 201.8–327.3, and 199.1–346.7 cm, respectively, ear heights ranged from 93.2 to 186.0, 64.6–146.5, 70.5–170.0, 71.1–168.3, and 66.2–150.7 cm, respectively, and ear ratios ranged from 0.33 to 0.49, 0.26–0.47, 0.26–0.49, 0.35–0.54, and 0.32–0.50, across all sites and years. Furthermore, the mean internode length and mean internode length below the primary ear were found to be the main contributors to the differences in plant height and ear height, respectively. Additionally, the results of stepwise regression indicated that both plant height and ear height were mainly affected by photoperiod and minimum temperature but the major climatic variables influencing ear ratio varied among different cultivars. Moreover, a linear model showed that, for every 10 cm increase in maize plant height, the DM at silking, DM at physiological maturity, and grain yield increased by approximately 0.41 t ha−1, 0.87 t ha−1, and 0.38 t ha−1, respectively. [ABSTRACT FROM AUTHOR]

• Genetic gain in yield was 111.4 kg ha−1 year−1 from the 1980s to 2010s in China. • Global gain in yield potential was 559.3 kg ha−1 year−1. • Breeding contribution to potential yield was 18.0 % under an optimal environment. • Breeding effect reduced the leaf angle above ear and ear ratio significantly. • Breeding effect increased the photosynthetic capacity significantly. The potential grain yield of maize increased tremendously from the 1980s to 2010s, as did the optimal plant density. However, cultivars were always bred in different environments owing to the varied eras in which they were created. To analyze the effect of genetic improvement on maize grain yield and related traits, we selected six hybrids from different eras for a detailed field study without water and fertilizer stress in 2017 and 2018 at Qitai Farm (89°34′E, 44°12′N), Xinjiang, China. The hybrids were selected based on the highest yields recorded in different years from 300 maize cultivars that had undergone 15 years of field testing. The maximum yield gap was approximately 20 % under the density with maximal yield measured from cultivar SC704 (the oldest cultivar) to DH618 and MC670 (the most recent cultivars) during the two experimental years. The global gain in yield potential was 559.3 kg ha−1 year−1 or 3.4 % with year of release (YOR−1). The genetic gain in grain yield was 111.4 kg ha−1 year−1 (0.62 % YOR−1) during the experimental years. The genetic contribution to potential grain yield was 18.0 %. Further analysis on the genetic progress of phenotypic traits showed that the leaf angle above ear decreased significantly by 0.26° year−1 (1.1 % YOR−1), which optimized the light distribution in the canopy and significantly improved the radiation use efficiency (RUE, 0.0286 g MJ−1 year−1 or 0.9 % YOR−1). The ear ratio decreased significantly by 0.0034 year−1 (0.71 % YOR−1). Other morphological traits did not change significantly with the year of release, indicating that the breeding of maize cultivars from the 1980s to 2010s primarily focused on the leaf angle above ear and ear ratio in phenotype. For the physiological traits, the leaf area duration (LAD) increased by 0.4097 m2·d year−1 (1.1 % YOR−1), and the photosynthetic rate at maturity significantly increased by 0.268 μmol CO 2 m−2 s−1 year−1 (3.7 % YOR−1), which finally significantly increased the total biomass by 0.285 Mg ha−1 year−1 (0.96 % YOR−1) and harvest index (HI) by 0.0021 year−1 (0.45 % YOR−1). Therefore, 18.0 % of the increased yield potential from the 1980s to 2010s was contributed by breeding under an optimal environment, among which the leaf angle above ear, ear ratio, LAD, photosynthetic capacity at maturity, biomass accumulation and HI played an important role for this genetic contribution. [ABSTRACT FROM AUTHOR]