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A field experiment was performed to study the effects of waterlogging on the leaf mesophyll cell ultrastructure, chlorophyll content, gas exchange parameters, chlorophyll fluorescence, and malondialdehyde (MDA) content of summer maize (Zea mays L.) hybrids Denghai605 (DH605) and Zhengdan958 (ZD958). The waterlogging treatments were implemented for different durations (3 and 6 days) at the third leaf stage (V3), the sixth leaf stage (V6), and the 10th day after the tasseling stage (10VT). Leaf area index (LAI), chlorophyll content, photosynthetic rate (Pn), and actual photochemical efficiency (ΦPSII) were reduced after waterlogging, indicating that waterlogging significantly decreased photosynthetic capacity. The chloroplast shapes changed from long and oval to elliptical or circular after waterlogging. In addition, the internal structures of chloroplasts were degenerated after waterlogging. After waterlogging for 6 d at V3, the number of grana and grana lamellae of the third expanded leaf in DH605 were decreased by 26.83% and 55.95%, respectively, compared to the control (CK). Those in ZD958 were reduced by 30.08% and 31.94%, respectively. Waterlogging increased MDA content in both hybrids, suggesting an impact of waterlogging on membrane integrity and thus membrane deterioration. Waterlogging also damaged the biological membrane structure and mitochondria. Our results indicated that the physiological reactions to waterlogging were closely related to lower LAI, chlorophyll content, and Pn and to the destruction of chloroplast ultrastructure. These negative effects resulted in the decrease of grain yield in response to waterlogging. Summer maize was the most susceptible to damage when waterlogging occurred at V3, followed by V6 and 10VT, with damage increasing in the wake of waterlogging duration increasing. [ABSTRACT FROM AUTHOR]

The greenhouse effect caused by global warming was becoming more and more obvious, resulting in increased frequency of high temperature and high humidity, which significantly affected maize productivity. However, it was poorly understood how the interactions of high temperature and high humidity affected leaf senescence, photosynthetic performance and yield of summer maize. Three stress treatments including (a) high temperature stress (T), (b) waterlogging stress (W) and (c) complex stress (T‐W) were set at the third leaf stage (V3), the sixth leaf stage (V6) and the tasselling stage (VT) in 2019–2020 to explore the influence mechanism of complex stress. Each stress treatment period lasted 6 days. Non‐stressed plants served as control. Yield, antioxidant enzyme activity, photosynthetic characteristics, and dry matter accumulation were determined. Our study found that the activity of antioxidant enzymes was significantly decreased, while malonyldialdehyde (MDA) accumulation was increased under each stress treatment. As a result, the photosynthetic characteristics were impaired, manifested in a significant decrease in net photosynthetic rate (Pn), enzyme activities of phosphoenolpyruvate carboxylase (PEPCase) and ribulose diphosphate carboxylase (RUBPCase). The decrease in photosynthetic intensity affected by each stress treatment led to a significant decrease in total dry matter accumulation and grain yield. The most significant effects of waterlogging and combined stresses on yield occurred at the V3 stage, followed by the V6 and VT stages. However, the most significant effects of high temperature occurred at the VT stage, followed by the V6 and V3 stages. Moreover, the compound stress exacerbated damage to leaf senescence and photosynthetic properties of summer maize compared to the single stress of high temperature or waterlogging. [ABSTRACT FROM AUTHOR]

It's well known that the development and distribution of roots could be regulated to obtain deep soil resource and enhance the grain yield by increasing the depth of fertilization, but little is known about whether increasing P fertilization depth can optimize the root distribution to delay leaf senescence, enhance photosynthetic performance and root-shoot coordination or not. We conducted a field experiment that tested the following four placement depths of P fertilization: 5 cm (P 5), 10 cm (P 10), 15 cm (P 15), and 20 cm (P 20). The experiment was designed to explore the regulatory effects of the P fertilization depth on the root growth and distribution, the photosynthetic performance, the root-shoot coordination, the yield formation, the N and P fertilizer utilization of maize plants. We found that deep P placement did indeed alter the root parameters. In the 20–60 cm soil layer, both the root dry weight and length of P 15 treatment were on average 23.2% higher than those of P 5 treatment. The specific root length and specific root surface area of P 15 treatment were 4.5% and 5.6% higher than those of P 5 treatment. In addition, the P 15 treatment achieved a significantly improved photosynthetic performance over the P 5 treatment: The leaf area index at the R6 stage was 10.2% higher, the leaf senescence index from the R2 to the R6 stages was 31.4% lower, the photosynthetic rate at the R3 stage was 25.9% higher. The P placement depth also optimized the root-shoot coordination: The ratios of root weight to shoot weight, root surface area to leaf area, and root length to leaf area of P 15 treatment were 6.7%, 13.8%, and 12.7% higher than those of P 5 treatment, respectively. Finally, the root P and N uptake efficiency, the photosynthetic P-use efficiency, and the physiological P-use efficiency of P 15 treatment were all significantly higher than those of P 5 treatments. And together these responses had the effect of increasing the mature biomass by 12.5%, and the grain yield by 22.0%. In conclusion, increasing the P fertilization placement depth to 15 cm regulates the growth and development of the root system, which in turn improves the capability of plant to uptake and utilize N and P in the soil, delays the onset of leaf senescence, enhances its photosynthetic performance and biomass accumulation rate, and thus ultimately increases the yield. [Display omitted] • Deep P fertilization optimizes root growth, and root-shoot coordination. • Deep P fertilization delays leaf senescence and improves photosynthetic performance. • Optimized root-shoot coordination improves the grain yield and nutrient use efficiency. [ABSTRACT FROM AUTHOR]

Background: Soil salt stress is a problem in the world, which turns into one of the main limiting factors hindering maize production. Salinity significantly affects root physiological processes in maize plants. There are few studies, however, that analyses the response of maize to salt stress in terms of the development of root anatomy and respiration. Results: We found that the leaf relative water content, photosynthetic characteristics, and catalase activity exhibited a significantly decrease of salt stress treatments. However, salt stress treatments caused the superoxide dismutase activity, peroxidase activity, malondialdehyde content, Na+ uptake and translocation rate to be higher than that of control treatments. The detrimental effect of salt stress on YY7 variety was more pronounced than that of JNY658. Under salt stress, the number of root cortical aerenchyma in salt-tolerant JNY658 plants was significantly higher than that of control, as well as a larger cortical cell size and a lower root cortical cell file number, all of which help to maintain higher biomass. The total respiration rate of two varieties exposed to salt stress was lower than that of control treatment, while the alternate oxidative respiration rate was higher, and the root response of JNY658 plants was significant. Under salt stress, the roots net Na+ and K+ efflux rates of two varieties were higher than those of the control treatment, where the strength of net Na+ efflux rate from the roots of JNY658 plants and the net K+ efflux rate from roots of YY7 plants was remarkable. The increase in efflux rates reduced the Na+ toxicity of the root and helped to maintain its ion balance. Conclusion: These results demonstrated that salt-tolerant maize varieties incur a relatively low metabolic cost required to establish a higher root cortical aerenchyma, larger cortical cell size and lower root cortical cell file number, significantly reduced the total respiration rate, and that it also increased the alternate oxidative respiration rate, thereby counteracting the detrimental effect of oxidative damage on root respiration of root growth. In addition, Na+ uptake on the root surface decreased, the translocation of Na+ to the rest of the plant was constrained and the level of Na+ accumulation in leaves significantly reduced under salt stress, thus preempting salt-stress induced impediments to the formation of shoot biomass. [ABSTRACT FROM AUTHOR]

The appropriate increase of planting densities is the key to the obtainment of high-yield maize (Zea mays L.). However, lodging is a major constraint to limit grain yield under increased planting density in present maize production. Effects of population density on stalk lodging and agronomic traits were investigated using two maize cultivars Denghai 618 (DH618, low stalk with low spike height) and Xianyu335 (XY335, high stalk with high spike height). Four levels of density treatment were imposed by 1.5, 6.0, 7.5, and 9.0 × 104 plants ha−1. Results showed that bending strength, rind penetration strength, maximum bending strength, dry weight, and internode diameter of maize were significantly decreased with the increase of planting density. The change range of XY335 with the increase of planting density was significantly larger than that of DH618, showing a high sensitivity to planting density. In addition, the thickness of cortex and vascular bundle sclerenchyma cells was significantly reduced with the increase of planting density. Compared with 1.5 × 104 plants ha−1, the thickness of the above-ground third internode stem cortex was decreased by 9.64%, 12.72%, and 20.77% for DH618, and 19.26%, 30.49%, and 37.45% for XY335 at 6.0, 7.5, and 9.0 × 104 plants ha−1, respectively. The thickness of vascular bundle sclerenchyma cells at 1.5 × 104 plants ha−1 was decreased by 7.75%, 12.44%%, and 17.89% for DH618, 10.18%, 15.21%, and 24.73% for XY335, compared to those at 6.0, 7.5, and 9.0 × 104 plants ha−1, respectively. Visibly, with the increase of planting density, the thickness of cortex and vascular bundle sclerenchyma cells, and the number of vascular bundles were all significantly decreased, resulting in the increase of lodging rate. However, the extent of variation in these parameters for short-plant height hybrid was less than those for high-plant height hybrid, and the yield of short-plant height hybrid was greater than that of high-plant height hybrid, indicating that short-plant height hybrid has better resistance to lodging with higher yield at higher planting density. Therefore, lodging resistance and yield can be improved through selection and breeding strategies that achieving synergistic development of diameter, dry weight per unit, and cortex thickness in maize basal internodes. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is a nutrient element necessary for plant growth and development. However, excessive inputs of N will lead to inefficient use and large N losses to the environment, which can adversely affect air and water quality, biodiversity and human health. To examine the effects of controlled-release fertilisers (CRF) on yield, we measured ammonia volatilisation, N use efficiency (NUE) and photosynthetic rate after anthesis in summer maize hybrid cultivar Zhengdan958. Maize was grown using common compound fertiliser (CCF), the same amount of resin-coated controlled release fertiliser (CRFIII), the same amount of sulphur-coated controlled release fertiliser (SCFIII) as CCF, 75% CRF (CRFII) and SCF (SCFII), 50% CRF (CRFI) and SCF (SCFI), and no fertiliser. We found that treatments CRFIII, SCFIII, CRFII and SCFII produced grain yields that were 13.15%, 14.15%, 9.69% and 10.04% higher than CCF. There were no significant differences in grain yield among CRFI, SCFI and CCF. We also found that the ammonia volatilisation rates of CRF were significantly lower than those of CCF. The CRF treatments reduced the emission of ammonia by 51.34% to 91.34% compared to CCF. In addition, after treatment with CRF, maize exhibited a higher net photosynthetic rate than CCF after anthesis. Agronomic NUE and apparent N recovery were higher in the CRF treatment than in the CCF treatment. The N uptake and physiological NUE of the four yield-enhanced CRF treatments were higher than those of CCF. These results suggest that the increase in NUE in the CRF treatments was generally attributable to the higher photosynthetic rate and lower ammonia volatilisation compared to CCF-treated maize. [ABSTRACT FROM AUTHOR]

With the extensive promotion of controlled-release urea (CRU), its N-release pattern has been shown to match the crop's N-demand period and improve crop yield by reducing N losses. Nevertheless, the impacts of CRU on summer maize yield, especially on greenhouse gas emissions, have rarely been reported during its long-term use. It is necessary through long-term positioning field experiment with CRU application to investigate the regulatory mechanisms of maize yield formation, nitrogen use efficiency (NUE), ammonia volatilization and greenhouse gas emissions. The long-term fertilizer positioning experiment for ten years, four treatments were performed: polymeric-coated controlled-release urea (CRF, 42% N, 3-months controlled-release period), sulfur-coated controlled-release urea (SCF, 35% N, 3-months controlled-release period), common urea (CCF, 46% N) and no nitrogen fertilizer (CK). Results showed that the two coated controlled-release fertilizers significantly increased NUE and dry matter accumulation in summer maize, and ultimately improved grain yield. Compared to CCF, CRF and SCF treatments increased post-silking dry matter accumulation by 16.3% and 13.3%; NUE by 42.3% and 28.9%. The 2-year mean grain yield of CRF and SCF treatment increased 9.0% and 12.4% compared to CCF treatment. CRF treatment significantly increased the NO 3 --N content in 0–60 cm soil layer; while CRF and SCF treatments showed a significantly higher NH 4 +-N concentration in the 0–20 cm soil layer than CCF treatment. Compared to CCF treatment, the CRF and SCF treatments significantly reduced peak ammonia volatilization, and the average cumulative emissions of ammonia volatilization of two years were reduced by 80.8% and 53.2%, respectively. CRF treatment had lower peak of N 2 O emissions but longer N 2 O emission duration than other N application treatments. The two-year average cumulative N 2 O emissions from CRF treatment increased by 49.6%, and SCF treatment increased by 61.1% compared to CCF treatment. Compared to CK treatment, total cumulative CH 4 uptake was 36.1% lower in CRF treatment, 60.9% in SCF and 78.9% in CCF treatment. The higher cumulative N 2 O emissions from CRF and SCF treatment resulted in a significantly higher global warming potential (GWP) than CCF treatment. The two-year mean increase in greenhouse gas intensity (GHGI) was 36.2% for CRF treatment and 44.7% for SCF treatment compared to CCF treatment. Long-term application of coated controlled-release fertilizers could achieve high yields and nitrogen use efficiency. However, there is a risk of increased N 2 O emissions, causing elevated GHGI. In the future, it is necessary to strengthen the research on the comprehensive effects of long-term reduced application of CRU on crop yield and greenhouse gas emissions, in order to promote the wide application of environmentally friendly CRU in the field. [Display omitted] • Long-term application of CRU could achieve sustainable crop yield improvement. • Long-term application of CRU significantly reduced ammonia volatilization and CH 4 emissions. • Long-term application of CRU carried the risk of increased N 2 O emissions, leading to higher GHGI. [ABSTRACT FROM AUTHOR]

How to improve nitrogen (N) efficiency and reduce environmental pollution caused by N loss has attracted much attention. However, limited research has lacked a comprehensive exploration of the effects of applying UAN under the micro sprinkling fertigation on reactive N (Nr), fertilizer efficiency and net benefits including environmental costs, plus associated responses of the microbial metagenome. The aim of this study was to assess the impact of N management practices on maize yield, Nr losses, and soil microbial community composition and function. Urea and urea ammonium nitrate solution (UAN) were used as N sources, and three N application rates (210, 168 and 0 kg N ha−1) and two fertilization methods (micro sprinkling fertigation and traditional fertilization) were set as the three key components. The results showed that micro sprinkling fertigation treatments reduced Nr losses, increased yield and N efficiency. Compared with urea, the total NH 3 volatilization and N 2 O emissions of UAN under micro sprinkling fertigation were decreased by 14.8% and 30.6%, respectively. Furthermore, the N reduction (FU1) treatment promoted plant N uptake, was saved 20% of N by affecting soil NH 4 +- N and NO 3 --N content, compared to that of urea, and it regulated the microbial abundance of N cycle function related to denitrification and N respiration, reduced global warming potential and greenhouse gas emission intensity. N application method, N source and N rate affected the diversity and composition of soil bacterial community, and altered Nr emissions by changing the abundance of functional microorganisms related to N cycle. Overall, improved N management practice was more conducive to increasing maize yield and net income, saving N resources, and reducing the risk of environmental damage. Our results contribute to a comprehensive understanding of the impact of N management on summer maize production, providing an effective N management practice that is conducive to "green agricultural development". [Display omitted] • A field trial was conducted in Huang-Huai-Hai Plain of China to clarify N losses and net income. • The soil bacterial community was changed by fertilization methods and N sources. • Applying UAN under micro sprinkling fertigation improved maize yield and saved N resources. [ABSTRACT FROM AUTHOR]

In order to improve the grain yield of food crops, which is necessary to ensure food security, it is crucial to narrow existing yield gaps. Quantitative analyses of crop yield gaps can provide theoretical support for ascertaining the primary cause of these yield gaps, and then it can be used to increase the grain yield. We evaluated the size and characteristics of the summer maize yield gap in the North China Plain by combining crop models, farmer surveys, and farm experiments. We simulated the summer maize population of farmers' yield level, attainable yield level and potential yield level by establishing three cultivation modes: traditional farming practices (FP), established high-yield and high-efficiency practices (HH) and super-high-yield practices (SH), and introduce the cultivation relying solely on the basic soil fertility (BSF) to reveal the impact of environmental and management factors on yield gap. We explored the driving factors causing observed variations of yield gaps through a quantitative analysis of several additional parameters that are commonly used to characterize the efficiency of the maize production process, including the contribution rates of dry matter and harvest index to grain yield, the radiation interception rate and the radiation conversion efficiency. Our results show that the total yield gap based on farmer surveys and crop models was 4.9 t ha-1, accounting for 37% of the potential yield, of which 46% was exploitable. The total yield gap based on the farm experiments was 3.9 t ha-1, accounting for 30% of the potential yield, of which 69% was exploitable. The grain yield of FP significantly positively correlated with the grain yield of BSF, HH and SH. The contribution rates of dry matter and harvest index to grain yield of FP treatment were 45.7% and 54.3%, respectively. With the increase of yield level, the contribution rate of dry matter increased and the contribution rate of harvest index decreased. In summary, we found a sizeable total yield gap in summer maize in the North China Plain, and a considerable part is exploitable. Optimizing integrated agronomic management has a great potential for closing the exploitable yield gap. Narrowing the yield gap requires a synergistic increase in the contribution rate of dry matter and harvest index to grain yield, but a substantial increase in dry matter is more important. At present, narrowing the exploitable yield gap requires synergistic improvement of radiation interception rate and radiation conversion efficiency to increase the dry matter of maize population. In the future, the regulation measures aiming at narrowing the unexploitable yield gap should further focus on improving the radiation conversion efficiency. • Quantification of the exploitable and unexploitable yield gaps for maize in the NCP. • Dry matter and harvest index contributions to maize grain formation depend on the yield level. • Suggestions for improving the productivity of established maize farming practices. [ABSTRACT FROM AUTHOR]

Controlled release urea (CRU) has been widely adopted to increase nitrogen (N) use efficiency and maize production, but the impacts can range widely depending on water availability in the soil. In an experiment using Zhengdan 958 (a popular summer maize hybrid), three levels of water treatments (adequate water condition [W3], which maintained soil moisture at about 75% ± 5% of the soil’s field capacity; mild water stress [W2], which maintained moisture content at 55% ± 5% of field capacity; and severe water stress [W1], which had a moisture content of 35% ± 5% of field capacity) and four levels of controlled release urea fertilizer (N0, N1, N2 and N3 were 0, 105, 210 and 315 kg N ha–1, respectively) were compared in a rainout shelter system with soil. The results revealed that CRU had significant effects on maize yields and N use efficiencies under different water conditions. The mean yields increased with increasing water levels and showed significant differences. Under W1, the accumulation of dry matter and N were limited, and N internal efficiency (NIE) and the apparent recovery efficiency of applied N (REN) decreased with N increases; yields of N1, N2, and N3 were similar. Under W2, the dry matter and N accumulation, as well as the yield, showed an increasing trend with an increase in N application, and the NIE and REN of N3 showed no difference from N2. Under W3, yields of N2 and N3 were similar and they were significantly higher than that of N1, but the agronomic N use efficiency (ANUE), REN, and the physiological NUE (PNUE) of N2 were 54.2, 34.9, and 14.4% higher, respectively, than those of N3. N application beyond the optimal N rate did not consistently increase maize yield, and caused a decrease in N use efficiencies. Highest overall dry matter, N accumulation, and yields were observed with N3 under W2, and those showed no differences with N2 and N3 under W3. Under this experimental condition, the CRU of 210 kg ha–1 was optimized when soil moisture content was 75% ± 5% of field capacity, but an N rate of 315 kg ha–1 was superior when soil moisture content during the entire growing season was maintained at 55% ± 5% of field capacity. [ABSTRACT FROM AUTHOR]

In maize, inferior grains (IG) located on the upper part of the ear have poor grain filling process compared to superior grains (SG) located on the middle and lower parts of the ear. This difference limits satisfactory yield and quality; however, the underlying molecular mechanisms remain unknown. Here, using the isobaric tag for relative and absolute quantification (iTRAQ) technology, the proteomes of IG and SG during early and middle grain filling stages were investigated. In total, 4720 proteins were identified in maize grain and 305 differentially accumulated proteins (DiAPs) were detected between IG and SG. These DiAPs were involved in diverse cellular and metabolic processes with preferred distribution in protein synthesis/destination and metabolism. Compared to SG, DiAPs related to cell growth/division and starch synthesis were lag-accumulated and down-regulated in IG, respectively, resulting in smaller sink sizes and lower sink activities in IG. Meanwhile, impediment of the glycolysis pathway in IG may lead to reduce energy supply and building materials for substance synthesis. Additionally, reactive oxygen species (ROS) homeostasis and the defense system were disturbed in IG, which might lead to reduce protection against various environmental stresses. The present study provides new information on the proteomic differences between IG and SG, and explains possible molecular mechanisms for poor grain filling in IG. [ABSTRACT FROM AUTHOR]

Excising the upper leaves strata of maize crops cultivated at high stand densities could possibly optimize canopy architecture to achieve enhanced canopy apparent photosynthesis, a more favorable distribution of 13 C-photosynthates to grain, and ultimately higher grain yields. To test this hypothesis, we conducted a leaf removal experiment in 2012 and 2013 growing seasons in Shandong, a province in the North China Plain. Jinhai5, a corn cultivar planted widely across China, was grown at a density of 105,000 plants ha −1 until 3 days after silking (DAS), when plants were subjected to the removal of the uppermost and next leaves (S 2 ), the four uppermost leaves (S 4 ) or the six uppermost leaves (S 6 ), with no leaf removal as control (S 0 ). In the S 2 treatment we found a longer duration of canopy apparent photosynthesis (CAP) and green leaf area index (LAI), higher total dry matter weight at physiological maturity as well as greater harvest index (HI) compared to the control, whereas those in the excessive leaf removal treatments (S 4 and S 6 ) declined substantially. In addition, modification of the number of leaves above the ear leaf led to different patterns of allocation of 13 C-photosynthates. Excising two leaves promoted the distribution of 13 C-photosynthates to grains, while that allocation decreased in the S 4 and S 6 treatments, which can be interpreted as a result of increased retention of 13 C-photosynthates in the stem and ear bracts. Plants in S 2 treatment displayed a yield advantage under high plant density due to higher kernel weight and more harvested ears. Relative to control, plants in the S 2 treatment had 15% and 12% higher grain yields in 2012 and 2013, respectively. However, the removal of four or six leaves at the very early grain filling period, when kernel sink capacity is being established, caused a marked reduction in yields due to decreased both kernel number per plant and kernel weight, despite a relatively higher biomass availability per kernel. In conclusion, excising two leaves (the uppermost and next leaves) of maize crops cultivated at high plant density delayed leaf senescence, enhanced canopy photosynthesis and dry matter accumulation, leading to a higher post-silking source–sink ratio with its positive impact on kernel weight and higher grain yield. [ABSTRACT FROM AUTHOR]

To explore the response of summer maize leaf senescence, photosynthetic characteristics, and yield to the depth of one-time base application of controlled-release urea, which provides a theoretical basis for the light and simplified production of summer maize. Seven treatments were set up with Zhengdan 958 as the material under field conditions, including no nitrogen fertilizer (CK), surface spreading (DP0), furrow application depth of 5 cm (DP5), 10 cm (DP10), 15 cm (DP15), 20 cm (DP20), 25 cm (DP25). The results showed that under the same nitrogen application rate, there are significant differences in the effects of summer maize leaf senescence and photosynthetic characteristics with the increase of fertilization depth, and DP10 and DP15 have the best effects. The LAI of DP10 and DP15 increased by 5.1% and 5.5% compared to DP0 at tasseling stage, and chlorophyll content increased by 6.8% and 7.3% in 10 days after tasseling. Compared with DP0, superoxide dismutase (SOD) increased by 13.1% and 10.5%, the content of soluble protein increased significantly, while the content of malondialdehyde (MDA) decreased by 9.8% and 10.8%, respectively. In addition, Pn and Gs of the ear-leaf significantly increased by 13.9%, 16.5%, and 26.1% and 31.9% at tasseling stage, respectively, over DP0, while Ci decreased by 22.3% and 26.4%, respectively; meanwhile, the photochemical quenching (qP) and quantum yield (ΦPSII) of the reaction center of photosystem II (PSII) of the ear-leaf were significantly improved, the non-photochemical quenching (NPQ) was significantly reduced. The yield of DP10 and DP15 heightened significantly; two-year average value increased by 5.7% and 6.0% compared with DP0; the kernels per spike and 1000-kernels weight increased by 4.8%, 5.2%, and 4.1%, 5.2%, respectively. Comprehensive analysis of LAI, chlorophyll content, various protective enzyme activities and MDA, soluble protein content showed that 10–15 cm is the appropriate fertilization depth when the nitrogen application rate of controlled-release urea is 225 kg N per hectare. In consequence, optimizing fertilization depth of controlled-release urea as a simplified fertilization mode could improve the nitrogen utilization efficiency and obtain higher yield in summer maize, which provides technical support for large-scale application of controlled-release urea. [ABSTRACT FROM AUTHOR]

• A moderate nitrogen rate ensures appropriate nitrogen content in leaves. • An appropriate nitrogen content in leaves affects grain yield formation by adjusting spike differentiation. • The leaf-N status influences spike differentiation through N accumulation and transport. Spike differentiation plays a pivotal role in maize (Zea mays L.) yield formation. However, it is unclear if leaf-N status affects yield formation by modifying spike differentiation. To understand how the spike differentiation is affected by leaf N content, as affected by the N rate, a field experiment was conducted. The experiment consisted of four N rates: N0 (0 kg N ha–1), N1 (129 kg N ha1), N2 (184.5 kg N ha−1), and N3 (300 kg N ha−1). At zero (N0) or low (N1) N rate, N stress significantly reduced the leaf N content of summer maize, which in turn reduced the N accumulation and N transfer from leaves to spike during spike differentiation, compared to the moderate N rate (N2), especially at the tassel-floret and ear-spikelet differentiation stage (FT-SE). So the reproductive growth was delayed by 2–4 days under N0 and N1, abortive florets of the ear were increased by 28.2–166.2 %, and the anthesis-silking interval was lengthened by 2–4 days, compared with N2, which reduced the kernel set and subsequently the silk and grain number per ear. Appropriate N rate (N2) could increase N metabolism-related enzymatic activities and increase the content of glutamine (Gln) and asparagine (Asn) in leaves, which in turn increased N transfer to spike to promote spike differentiation and decrease abortive florets. Finally, the silk and kernel set under N2 were increased, which resulted in an increased in grain number per ear and yield by 3.5–27.4 % and 13.1–41.8 %, respectively, compared with N0 or N1. However, the excessive N rate (N3) demonstrated a threshold, which no longer promoted spike differentiation. Moreover, leaves had an N-absorption peak at the FT-SE, and the N content positively correlated with the total numbers of silks and florets per ear. The efficient absorption of N at the FT-SE was beneficial to increase floret fertility. Collectively, a moderate N fertilizer rate (around 185 kg N ha−1) assured appropriate N accumulation in leaves and N transfer to spike, improved spike development and increased floret fertility, grain number and yield. [ABSTRACT FROM AUTHOR]