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Solar radiation is an important environmental factor affecting maize (Zea mays L.) root and shoot growth and grain yield. This study was conducted in Qitai and Yinchuan, China, in 2018 and 2019. The maize cultivars of XY335, ZD958, and DH618 and planting densities of 7.5 × 104 (D1) and 12 × 104 plants ha−1 (D2) were adopted under shading levels of 15 (S1), 30 (S2), and 50% (S3) with natural light as the control (CK). The results showed that averaging all shading and density treatments over the 2 yr, shading reduced the grain yields of XY335, ZD958, and DH618 by an average of 40.4, 39.2, and 35.6%, respectively, compared with the CK. The effect of solar radiation on the root dry weight was greater than that on the shoot dry weight, which resulted in a decrease in root/shoot ratio with increasing shading level. The quantitative analysis results showed that for every 1‐MJ m−2 decrease in solar radiation, the root dry weight, shoot dry weight, and root/shoot ratio decreased by 0.1938 g m−2, 1.3517 g m−2, and 0.0103 × 10−2, respectively. According to this quantitative relationship, it was helpful to select cultivars and planting density with suitable root characteristics under different solar radiation conditions in different regions. From the aspects of shoot and grain yield, DH618 was more shade resistant, and its root system rapidly adjusted to compensate for shoot growth and yield formation when solar radiation decreased. Such cultivars should be given attention in future production and breeding. [ABSTRACT FROM AUTHOR]

The effects of uniformity in border rows and population structure on the yield of hybrid maize (Zea mays L.) grown at high planting density was studied in field experiments at Qitai Farm (89°34′E, 44°12′N), Xinjiang, China, during 2013 and 2014. The experiments incorporated a planting density of 12.0 plants m–2 and three maize cultivars (M753, LY66, LD565). Border effects and uniformity in the border rows were studied at the silking and maturity stages. Yields of M753, LY66 and LD565 were 16.46, 15.02 and 11.45 Mg ha–1, respectively. Analysis of yield components in border rows indicated that the number of kernels per ear, 1000-kernel weight and yield per plant of M753 stopped decreasing after the second row in the border, whereas those of LY66 and LD565 stopped decreasing after the third row in the border, demonstrating a stronger border effect. The cultivars intercepted >95% of the light, but light transmission was lower for M753 than for LY66 and LD565, which resulted in the highest light interception in the upper canopy layers of M753. Analysis of uniformity in the border rows showed that the uniformity values for plant height, ear height, stem diameter, number of kernels per ear, 1000-kernel weight and yield per plant were higher for M753 than for LY66 and LD565. For the three cultivars, uniformity values could be ranked in the order plant height > ear height > stem diameter. The results suggest that cultivars with weaker border effects and greater uniformity in border rows can produce higher yields when grown at a high planting density. The magnitude of margin effect reflects the density-tolerance of maize cultivars. Uniformity plays an important role in higher maize yield achievement especially under high planting density. The weakest marginal effects and greatest uniformity in border rows were closely related to higher grain yield. [ABSTRACT FROM AUTHOR]

Meeting maize (Zea mays L.) production targets of high grain yields and nitrogen use efficiency (NUE) requires the development of stress‐tolerant cultivars and corresponding cultivation practices that maximize efficiency. Therefore, our objectives were to (i) determine the impacts of N application rate, planting density, and maize cultivar (which have improved with each successive release date) on the N partial productivity factor (PFPN) and N agronomic efficiency (AEN), and to (ii) characterize the responses of maize cultivars indexes to different cultivation conditions. We found that maize PFPN and AEN values were affected by N application, planting density, and cultivar. The PFPN and AEN declined with increasing N but increased with increasing planting density or genetic improvement (i.e. later year of release). The responses of PFPN and AEN to planting density and N application, taken either as single factors or as interacting factors, were greater for recently released cultivars than for older cultivars. The PFPN and AEN values were not automatically associated with maize yields, indicating that the genetic improvements that led to increases in PFPN and AEN were due to unconscious selection. Thus, improvements in NUE resulted from improvements in cultivars' tolerance to planting density stresses and from cultivation practices that employed higher planting densities from the 1950s to 2010. [ABSTRACT FROM AUTHOR]

Nitrogen is an essential element for maize (Zea mays L.). Farmers in developed countries most often apply more N fertilizer than necessary, which reduces N use efficiency (NUE). Improving radiation and N distribution, and thus the NUE of modern maize production systems with high plant density, is of great significance. In this study, field experiments were conducted in 2014 and 2015 in Xinjiang, China, using hybrid maize cultivar DH618 with high density. In addition, a synthesis analysis was conducted using data from 95 publications to observe N characteristics under different yield levels and compare the experimental results with existing studies. The relationship between radiation and N distribution in the canopy of high‐yield maize was also assessed. Nitrogen uptake was significantly correlated with grain yield. However, N uptake per unit grain yield and grain N concentration at maturity decreased as grain yield increased. The positive correlations between radiation and leaf and stalk N concentrations at silking showed that N concentration at silking increased as the height of the canopy layer increased because of increased radiation in the canopy. These results indicate that maize hybrids with erect upper leaves and high post‐silking N uptake can coordinate and optimize the distribution of radiation and N in different canopy layers and thus improve NUE and yield under high‐density production. [ABSTRACT FROM AUTHOR]

High yield is one of the important goals of crop production, and close planting and optimum irrigation systems are important agronomic practices for increasing maize (Zea mays L.) grain yield. However, little is known about the effect of optimal irrigation interval on the photosynthetic rate (Pn) and dry matter accumulation (DM) of closely planted super-high-yield maize under drip irrigation under mulch. Therefore, the objective of this study was to determine the effects of irrigation interval on the leaf Pn, DM, and grain yield of closely planted super-high-yield maize under mulch drip irrigation in the Xinjiang Uygur Autonomous Region, Northwestern China. A field experiment was conducted using three irrigation intervals in 2016—namely, six days (D6), nine days (D9), and 12 days (D12)—and five irrigation intervals in 2017—namely, three days (D3), six days (D6), nine days (D9), 12 days (D12), and 15 days (D15). The Xianyu 335 high-yield maize hybrid was used in the test; the planting density was set to 12×104 plants ha−1, and an optimal irrigation quota of 540 mm was used. The results showed that during the irrigation period, (1) the soil moisture content (SMC), DM, leaf Pn, and grain yield of treatment D6 were higher than for other irrigation intervals, (2) the leaf Pn and stomatal conductance (GS) of the leaves of treatments D3, D9, D12, and D15 were significantly correlated with the SMC of the 0–40 cm soil layer, and (3) the leaf Pn of treatment D6 was significantly positively correlated with SMC in the 0–60 cm soil layer but not significantly correlated with GS. Irrigation treatment D6 was found to maintain high SMC, provide a water environment favorable to the growth of maize, and increase the leaf Pn and DM, and thereby obtain maize grain yield (20.6–21.0 t ha−1). Therefore, an optimal irrigation interval could be beneficial for adjusting soil moisture, leaf Pn, and DM in order to increase maize grain yield with drip irrigation under mulch. [ABSTRACT FROM AUTHOR]

• Increasing crop yields while reducing environmental impacts are a great challenge to ensuring food security and environmental quality. • Increasing plant density appropriately is one of the most effective strategies for increasing maize yield worldwide. • Overuse of nitrogen (N) fertilization on maize is popular and has resulted in excessive N surplus in the soil in China. • Maize yield were increased by 5.59% through increasing plant density without extra N inputs and meanwhile reactive N losses intensity and GHG intensity decreased by 2.2% to 10.2% across China. Increasing crop yields while reducing environmental impacts are a great challenge to ensuring food security and environmental quality for the world agriculture. Increasing planting density appropriately is one of the most effective strategies for increasing maize (Zea mays L.) yield. In China, overuse of nitrogen (N) fertilization on maize has resulted in excessive N surplus in the soil and environmental impacts. To address this challenge we conducted 212 site-year field experiments at two planting densities of 60000 and 75000 plants per ha with the same inputs of N. Results showed that maize yield could be increased 5.59% across China and 10.5%, 2.7%, 5.2% and 10.3% respectively in Southwest (SW), Huanghuaihai (HM), North (NM) and Northwest (NW) maize regions without extra inputs of N. The Life-cycle assessment showed that reactive N loss intensity and GHG intensity decreased by 2.2% to 10.2% across different regions of China, indicating that yield increase could be achieved without extra N inputs and further negative environmental impacts if planting density was increased by 15000 plants per ha under the current condition of excessive N surplus in China. If farmers in China increase maize planting density by 15000 per ha across the whole country the total maize production from the same planting area of 2017 would be 290 Mt which will be close to the expected demand of 315 Mt by 2030 while reducing the environmental impacts of intensive agriculture. [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]

Over three continuous years (2013–2015) of high-yield experiments, maize hybrid DH618 was grown at densities of 12.0 and 13.5 × 10 4 plants ha −1 at Qitai Farm (89°34′E, 44°12′N), Xinjiang, China, and broke the record for the highest yield in China. Therefore, it is considered to have plant characteristics that approach those of the ideotype. In 2014 and 2015, various canopy characteristics were measured. On average, the dry matter gain of hybrid DH618 was 20.0, and 36.5 Mg ha −1 during post-silking and at maturity, a transfer rate from vegetation organs of 8.7%, and harvest index of 0.54. On average, it had a leaf area index of 7.53 at silking, a leaf area of 3.99 × 10 3 and 1.90 × 10 3 cm 2 above and below the ear, and a spatial density of leaf area of 0.17 and 0.08 cm 2 cm −3 above and below ear, respectively. The average light transmissions were 3.7% and 1.1% at the ear and bottom respectively, and the attenuation coefficient was 0.63. The plant height and ear height were about 287 and 113 cm. The average leaf orientation values were 51.9 and 49.2 above and below ear, respectively. These results will be of great significance for ideotype breeding programs and maize yield improving. [ABSTRACT FROM AUTHOR]

Maize production in arid areas of Northwest China is seriously limited by water supply. Conserving irrigation water and increasing water use efficiency (WUE) are effective methods for sustainable agricultural development. The objectives of this study were to optimize irrigation water use, grain yield, WUE, and economic return of super high yield maize in a drip irrigation and plastic film mulch system in Xinjiang. Experiments were conducted in Qitia County, Xinjiang, and included four drip irrigation treatments: T1, 600 mm (CK); T2, 540 mm; T3, 480 mm; and T4, 420 mm. Six density-tolerant maize hybrids were planted in 2014 and 2015. Grain yield and economic return did not significantly change in response to a 10% decrease in irrigation level, whereas evapotranspiration decreased and WUE increased (4.61%–6.66%). High grain yield (15.7–19.1 Mg ha −1 ), WUE (2.47–2.77 kg m −3 ), and economic return (1691.6–2605.7 US$ ha −1 ) were achieved under the T2 treatment. The combined techniques of drip irrigation, plastic film mulching, and increased planting density improved yield. Quadratic relationships were found between irrigation level and grain yield and between irrigation level and economic return. Irrigation level and evapotranspiration were negatively correlated with WUE. Maximum economic return and irrigation level were linearly related with the price of water. Taking into account grain yield, economic return, and ecological effects, an irrigation amount of 540 mm is optimal for drip irrigation–plastic film mulching systems in arid areas. [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]

• Large genotypic barrenness differences were observed as cultivation improved. • Barrenness increments of older cultivars more than those of newer cultivars. • Maize barrenness can be decreased by breeding and better crop management. Genetic improvements have made substantial contributions to maize yield and the direction of these improvements has been influenced by cultivation conditions and climate factors. Maize plant and ear barrenness are important to grain yield so we intensively examined the barrenness responses of 10 maize cultivars, released at various times from the 1950s to 2010s in China, to cultivation improvements in plant density and nitrogen application. We compared the cultivars' responses at 4 nitrogen rates (0, 150, 225, 300 kg ha−1) and 4 plant densities (37,500, 52,500, 67,500, 82,500 plants ha−1) in three (2011–2013) growing seasons. The results showed earless plant rate (EPR), kernel number per ear (KNP), and kernel number per unit area (KN) were significantly affected by nitrogen, plant density, and cultivar. Plant density increases accelerated maize barrenness. EPR increments decreased significantly (about 0.4 % year−1) while the KNP decrements of older cultivars were greater than those of newer cultivars as plant density increased. Plant and ear barrenness decreased as N increased. But EPR decreases and KNP increases showed no significant linear trends with maize cultivars improved. As cultivation improved by increasing density and nitrogen together, differences in plant and ear barrenness between older cultivars and newer cultivars were revealed. Older cultivars were more sensitive to linked density and nitrogen increases. However, for all cultivars, barren plants and ears did not change significantly under contemporary cultivation practices, thus showing that new cultivars adapt well to both high density planting and high nitrogen supplementation. Maize barrenness can be decreased by breeding cultivars that cope well with density stress and by pursuing better crop management in the future. [ABSTRACT FROM AUTHOR]