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In recent years, the frequency and intensity of exposure to heat stress have increased gradually, seriously hampering the production of maize. This paper presents a study designed to analyze how the development, physiology and dispersal of pollen from the heat‐resistant maize variety Zhengdan958 and the heat‐sensitive maize variety Xianyu335 are affected by exposure to heat stress during the tasselling stage. Our results showed That exposure to heat stress significantly increased the antioxidant enzyme activity in pollen. Upon visual inspection of the pollen, we found that the lower water content had given rise to wrinkles in the pollen surface, sunken germination pores, and morphological deformations. In addition, the anther dehiscence process was hindered, resulting in a reduced amount of pollen being dispersed. We also found elevated levels of abscisic acid (ABA), jasmonic acid (JA) and its derivatives, indole acetic acid (IAA) and gibberellin‐3 (GA3) in heat‐pollens, as well as elevated ratios of IAA to ABA and ABA to GA3. Ultimately impaired pollen fertility. Summarizing, our experiment revealed that reduced pollen quantity and quality are significant contributors to fertility losses in summer maize exposed to heat stress at anthesis, and we hope that our analysis of the physiological mechanisms involved can contribute to the development of crop management measures aimed at countering the increasingly detrimental effects of heat stress on the production of summer maize. [ABSTRACT FROM AUTHOR]

Purpose: The developmental status of the male and female spike determines grain number (GN) per ear and yield. A better understanding of the effect of N on male and female spike differentiation and GN formation could help to gain insight into the mechanism of N regulation on yield. Methods: A field experiment was conducted with four nitrogen rates: 0 (N0), 129 (N1), 185 (N2), and 300 kg N ha−1 (N3) with a single summer maize hybrid to determine tassel and ear development and the resulting GN. Results: The expression of key proteins and genes related to fatty acid metabolism of N0 were down-regulated and the tapetum was abnormally degraded. This inhibited the synthesis of long-chain fatty acids (LCFAs) in the tassel and ear. Both pollen and silk development at the mononucleate stage were abnormal and presented as misshapen pollen, uneven silk tube, reduced silk, and poor pollination. Finally, anthesis-silking interval (ASI) was increased and the length of male and female spikes, fertilized florets, floret fertility percentage, and grain set rate were reduced in N0 treatment resulting in reduced GN. N application promoted fatty acid metabolism but N application greater than 185 kg N ha−1 did not increase LCFA of either male or female spike traits. Conclusions: A nitrogen rate of 185 kg N ha−1 was sufficient to promote lipid metabolism, and increase the content of LCFAs. This resulted in normal pollen and silk development, shortened ASI and led to an increase in the number of fertile florets, fertilization percentage, and GN. [ABSTRACT FROM AUTHOR]

Cytokinin is known to be involved in the regulation of plant responses to counteract the adverse effects of stress conditions. This work investigated the effects of exogenous spraying of 6-benzyladenine (6-BA) after water logging for 6 days at the third leaf stage (V-3WL + BA) and the sixth leaf stage (V-6WL + BA) on grain yield and growth of summer maize hybrids DengHai605 (DH605) and ZhengDan958 (ZD958), which are planted most popularly in China. Waterlogging under field conditions delayed the growth process, decreased leaf area index, chlorophyll content and dry matter accumulation, resulted in a significant reduction of grain yield with a decrease of 30.30% and 18.78% under V-3WL (water logging for 6 days at the third leaf stage) and V-6WL (waterlogging for 6 days at the sixth leaf stage) of DH605, 30.39% and 21.38% under V-3WL and V-6WL of ZD958, respectively, compared to the control (CK). By contrast, exogenous application of 6-BA effectively alleviated the adverse effects of waterlogging on summer maize by delaying leaf senescence, increasing chlorophyll content and improving photosynthetic performance. At tasseling stage, the P n of V-3WL + BA and V-6WL + BA in DH605 increased by 9.57% and 8.38%, respectively, compared to that of V-3WL and V-6WL, while the corresponding values for ZD958 increased by 2.96% and 4.05%, respectively. Those responses are conducive to the accumulation of photosynthetic products, increasing grain filling rate, and improving ear character, and then leading to increase grain yield of summer maize. Grain yield of DH605 under V-3WL + BA and V-6WL + BA increased by 15.57% and 12.39%, respectively, compared to that of V-3WL and V-6WL, while the corresponding values for ZD958 increased by 20.05% and 15.32%, respectively. Clearly, spraying exogenous 6-BA could effectively improve grain-filling characteristics and photosynthesis of waterlogged summer maize, resulting in a significant increase of grain yield, compared to water logging treatments. [ABSTRACT FROM AUTHOR]

Summer maize is frequently subjected to waterlogging damage because of increased and variable rainfall during the growing season. The application of 6‐benzyladenine (6‐BA) can effectively mitigate the waterlogging effects on plant growth and increase the grain yield of waterlogged summer maize. However, the mechanisms underlying this process and the involvement of 6‐BA in relevant signal transduction pathways remain unclear. In this study, we explored the effects of 6‐BA on waterlogged summer maize using a phosphoproteomic technique to better understand the mechanism by which summer maize growth improves following waterlogging. Application of 6‐BA inhibited the waterlogging‐induced increase in abscisic acid (ABA) content and increased the phosphorylation levels of proteins involved in ABA signaling; accordingly, stomatal responsiveness to exogenous ABA increased. In addition, the application of 6‐BA had a long‐term effect on signal transduction pathways and contributed to rapid responses to subsequent stresses. Plants primed with 6‐BA accumulated more ethylene and jasmonic acid in response to subsequent waterlogging; accordingly, leaf SPAD, antioxidase activity, and root traits improved by 6‐BA priming. These results suggest that the effects of 6‐BA on hormone signal transduction pathways are anamnestic, which enables plants to show faster or stronger defense responses to stress. [ABSTRACT FROM AUTHOR]

The North China Plain (NCP) is typically cropped using a winter wheat–summer maize double cropping system, which has huge potential for straw production. The region also experiences atmospheric pollution caused by straw burning, which has become an important contributor to global warming. The goals of this experiment were to resolve the conflict between soil fertility and greenhouse gas emission when using straw return to the field and to identify the best balance between environmental protection and agricultural production. A randomized block design with three replicates was used. The design included three treatments based on the return of all winter wheat stalks to the field: (1) all summer maize stalks were pulverized mechanically and returned to the field (SR); (2) half of the summer maize stalks were pulverized mechanically and returned to the field (1/2 SR); and (3) all summer maize stalks were fully removed (control: CK). This long-term test was performed for 6 years. Straw returned to the field significantly increased greenhouse gas emissions. The cumulative CO 2 emissions were higher by 32% under SR and by 17% under 1/2 SR compared with CK. The cumulative N 2 O emissions were higher by 28% under SR and 15% under 1/2 SR compared with CK. The greenhouse gas efflux increased with increased amounts of straw returned to the field. Compared with SR, 1/2 SR significantly reduced greenhouse gas emissions, while still ensuring sustainable soil fertility. Additionally, our research showed that the upper part of the corn stalk is better for generating biomass energy than the lower part. This study provides a theoretical basis for using the upper stalk for bioenergy and the lower stalk for direct return to the field for fertilization. Unlabelled Image [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Thousand-kernel weight increased with late harvest, increasing grain yield of summer maize. • Late harvest promoted N accumulation after tasseling and N translocation to grain. • N accumulation played a crucial role in the early and middle period, and N translocation did in the mid-late period. Abstract The farmers are accustomed to harvesting summer maize around September 20, but the maize has not yet reached physiological maturity in the Huang-Huai-Hai region, which is adverse for grain yield and mechanized harvest. In order to explore the effect of harvest date on grain yield and nitrogen utilization of summer maize, two treatment in 2016 (CK and 10d) and four treatments in 2017 (CK, 3d, 6d, 10d) were conducted. The sowing dates of all treatments were June 13, and the harvest dates of CK, 3d, 6d and 10d were September 20, 23, 26 and 30, respectively. We found that grain yield and thousand-kernel weight of 10d significantly increased by 17.4–19.8% and 16.8–19.6%, respectively, compared to CK. And partial factor productivity of nitrogen of 10d was 17.4–19.7% higher than that of CK. The grain nitrogen concentration of 3d, 6d and 10d increased by 5.4%, 9.0%, and 9.3–10.8% compared to CK, which promoted nitrogen harvest index, physiological nitrogen use efficiency and partial factor productivity of nitrogen. The reason why nitrogen utilization efficiency increased was that late harvest promoted nitrogen accumulation after tasseling and nitrogen translocation to grain. The nitrogen translocation of 6d was 10.0% in 2017 higher, and that of 10d was 25.1% in 2016 and 15.3% in 2017 higher, respectively, compared to CK. The nitrogen accumulation of 10d increased by 39.0% in 2016, and that of 3d, 6d and 10d increased by 46.5%, 51.3% and 57.3% in 2017, compared to CK. In conclusion, the thousand-kernel weight increased with the delay of harvest date, resulting in increases in grain yield of summer maize. The late harvest promoted nitrogen utilization efficiency resulting from higher nitrogen accumulation after tasseling and higher nitrogen translocation to grain. The contribution of nitrogen translocation to grain yield appeared in the mid-late period (September 23–30), while the contribution of nitrogen accumulation after tasseling did in the early and middle period (September 20–26). Considering annual production of winter wheat-summer maize, the optimized harvest date for summer maize is 6–10 days later than the conventional pattern in this study, that is the cumulative growing degree-days after tasseling reach 613.2–711.5 °C at least. [ABSTRACT FROM AUTHOR]

Low light is a type of abiotic stress that seriously affects plant growth and production efficiency. We investigated the response mechanisms of summer maize to low light by measuring the changes in endogenous hormones in the grains and during grain filling in summer maize at different light intensities to provide a theoretical basis for the production and management of summer maize under light stress. We applied different light treatments in a field experiment as follows: S, shading from tassel stage (VT) to maturity stage (R6); CK, natural lighting in the field; and L, increasing light from VT to R6. The shading level was 60%, and the maximum illumination intensity of the increasing light treatment on cloudy days was 1600-1800 μmol m−2 s−1. Compared with the control, shading significantly increased the grain abscisic acid (ABA) content at 5-20 days after pollination and decreased the indole acetic acid (IAA), zeatin riboside (ZR), and gibberellin (GA) contents (P < 0.05). The grain-filling rate decreased under shading conditions. Meanwhile, the grain volume, grain weight, and yield all decreased; the yields in 2013 and 2014 decreased by 61 and 60%, respectively. The grain IAA, ZR, and GA contents were increased by increasing light. The grain ABA content at 5-20 days after pollination did not significantly differ from that of CK (P < 0.05). After 20 days after pollination, the ABA content decreased, the grain-filling rate and the filling duration increased, and the yield increased. However, shading after anthesis increased the grain ABA content and reduced the IAA, ZR, and GA contents. Grain growth and development were inhibited, and the yield decreased. The grain ABA content decreased; the IAA, ZR, and GA contents increased; and the yield increased after increasing light. The results indicate that different light intensities regulated the levels of grains endogenous hormones, which influenced the grain-filling rate and duration, and consequently, regulated grain weight and yield. [ABSTRACT FROM AUTHOR]

Root growth and development of summer maize ( Zea mays L.) is an important process in determining grain yield. In comparison to the information on above ground plant responses only limited knowledge exists on the response of root growth and development to integrated agronomic practices management (defined as a comprehensive management framework consisted of tillage method, plant density, seeding and harvest date, and fertilizer application) under field conditions. Two experiments, integrated agronomic practices management (IAPM) and nitrogen rate testing (NAT) were used to determine the effects on summer maize root system in the course of five years in North China. IAPM consisted of four treatments (CK: local conventional cultivation practices, Opt-1: an optimized combination of cropping system and fertilizer treatment, HY: treatment based on high-yield studies, and Opt-2: a further optimized combination of cropping system and fertilizer treatment). NAT had four treatments of nitrogen rate (0, 129.0, 184.5, and 300.0 kg N ha −1 ).Individual/population root dry weight, individual/population absorption area, surface, volume, and length density of root and grain yield were measured. Roots were sampled per plot at six-leaf stage (V6), tasseling stage (VT), milk stage (R3) and physiological maturity stage (R6). The results from IAPM revealed that Opt-2 significantly increased dry weight, volume, superficial area, and length density of root across the 0–30 cm soil layer of whole growth period. Root active absorption area of Opt-2 exhibited a significant increase in the 0–30 cm soil layer of whole growth period except V6. In compare with root/shoot ratio of CK, this of Opt-2 increased by 14.5% at VT and 16.3% at R6. Results from NAT revealed that N with a range from 0 to 184.5 kg N ha −1 played a positive role in root growth and development. Dry weight, absorbing area of root, and the root/shoot ratio increased as N rate rise within certain limits and then decreased significantly. Dry weight, the proportion of deeply distributed, absorption area, length density of root, and root/shoot ratio increased due to appropriate population, reasonable fertilizer management, and suitable harvest date, which provided sufficient nutrients and moisture to aboveground parts for growth, development, and high grain yield of summer maize. [ABSTRACT FROM AUTHOR]

The maize production sector in the North China Plain (NCP) is facing the dual pressures of having to increase its grain yield and improve its environmental sustainability. Evaluating the yield gap and ascertaining the factors that limit the grain yield might suggest new approaches to address these challenges. The objective of this study was to estimate the yield potential and the yield gap associated with smallholdings in the NCP using a hybrid method; to determine the factors driving the grain yield and corresponding sustainability indicators; and to evaluate to what degree the introduction of scientifically developed high-yield and high-efficiency agronomic practices (HH) to smallholders might help to sustainably narrow the exploitable yield gap. Combined with diagnostic smallholder survey and crop modeling exercise to characterize and decompose yield gaps. With survey data, we assessed the existing variation with respect to various key performance indicators and carried out a number of controlled comparative experiments at farms (HH vs traditional farming practices (FP)) in multiple locations. Our work revealed the total and exploitable yield gap were 4.3 t ha−1 and 1.8 t ha−1 for rainfed summer maize, and 4.4 t ha−1 and 1.9 t ha−1 for irrigated summer maize across the entire NCP, indicating a large potential for yield improvements. The main factors driving the yield from the entire region were the planting density, the fertilization frequency, and the irrigation frequency. It should be noted that farmers whose yield was in the top 25% bracket of the yield distribution also achieved relatively high utilization efficiencies with respect to N, P, and K fertilizers (15%, 16%, and 16% above the average values, respectively) while their profit was 41% above average. Comparative experiments conducted over several seasons support insights from surveys by demonstrating that major gains in grain yield (+30%), the fertilizer utilization efficiency (+37% in N partial factor productivity, +48% in P partial factor productivity, and + 32% in K partial factor productivity) and economic profit (+62%) are achievable through the adoption of HH. Through a hybrid method, our results suggest that agricultural intensification can be achieved in the NCP without having to trade off yield against environmental sustainability. Evidently, smallholders can simultaneously improve their maize grain yield, fertilizer utilization efficiency, and profit by adopting straightforward non-disruptive optimizations of their agronomic practices. [Display omitted] • Mixed-method approach used to decompose maize yield gaps with crop model, diagnostic smallholder surveys, and controlled comparative experiments. • We found a sizeable total yield gap (4.3 and 4.4 t ha−1 for rainfed and irrigated maize) in the NCP, of which 1.8 and 1.9 t ha−1 is exploitable. • Main factors driving yield include the planting density, the N topdressing frequency, and the irrigation frequency. • High-yield farms had greater N, P and K fertilizer use efficiencies and increased economic profit. • Smallholder production could be improved by optimize agronomic practices and without having to trade off yield against environmental sustainability. [ABSTRACT FROM AUTHOR]

Regulation of ridge tillage on yield and growth of waterlogged summer maize hybrids Denghai 605 (DH605) and Zhengdan 958 (ZD958) were investigated in field conditions. Results showed that waterlogging significantly decreased leaf area index (LAI), SPAD value, and biomass, resulting in the reduction of photosynthetic rate, thereby decreased grain yield of summer maize. Grain yields of DH605 and ZD958 were decreased by 38% and 42% respectively, compared to no waterlogging treatment. However, ridge tillage was conducive to alleviate the adverse effects of waterlogging on photosynthetic performance and photosynthetic effective radiation by increasing LAI and SPAD value, and improving canopy structure. At tasseling stage (VT), the light transmittance of ear layer in ridge tillage treatment for DH605 and ZD958 was decreased by 12% and 19%, respectively, compared to that of waterlogging treatment. Visibly, ridge tillage effectively alleviated leaf senescence and the decrease of LAI and chlorophyll content induced by waterlogging, and improved canopy structure, photosynthetic effective radiation, and photosynthesis of waterlogged summer maize, and thus increasing grain yield by 39% and 50% for DH605 and ZD958, respectively, compared to waterlogging treatments. [ABSTRACT FROM AUTHOR]

Soil nitrogen (N) shortage is a problem which affects many developing nations. Crops grown with low soil N levels show a marked decrease in the rate of photosynthesis and this deficiency reduces crop yield significantly. Therefore, developing a better understanding of the mechanisms by which low N levels cause decreased photosynthesis is crucial for maize agriculture. To better understand this process, we assessed the responses of photosynthesis traits and enzymatic activities in the summer maize cultivar Denghai 618 under field conditions with and without the use of N fertilisers. We measured photosynthesis parameters, and compared proteome compositions to identify the mechanisms of physiological and biochemical adaptations to N deficiency in maize. We observed that parameters that indicated the rate of photosynthesis decreased significantly under N deficiency, and this response was associated with leaf senescence. Moreover, we identified 37 proteins involved in leaf photosynthesis, and found that N deficiency significantly affected light-dependent and light-independent reactions in maize leaf photosynthesis. Although further analysis is required to fully elucidate the roles of these proteins in the response to N deficiency, our study identified candidate proteins which may be involved in the regulatory mechanisms involved in reduced photosynthesis under low N conditions in maize. [ABSTRACT FROM AUTHOR]

A field experiment was conducted to study the effects of shading on tassel and ear development and yield formation of three summer maize hybrids Zhenjie 2 (ZJ2), Denghai 605 (DH605), and Zhengdan 958 (ZD958). The ambient sunlight treatment was used as control (CK) and shading treatments (40 % of ambient sunlight) were applied at different growth stages from silking stage (R1) to physiological maturity stage (R6) (treatment S1), from the sixth extended leaf stage (V6) to R1 (treatment S2) and from seeding to R6 (treatment S3). Shading had no significant effect on the time from seeding to shoot emergence (VE); however, subsequent growth and development were delayed with shading beyond this point. The differentiation time of both tassel and ear delayed, and female spike (tassel) floret differentiation, sexual organ formation time, and anthesis-silking interval (ASI) were lengthened. After shading, the total number of floret, silk, and fertilization floret reduced significantly; the number of abortive seeds increased, and the total setting percentage among different treatments showed that CK>S2>S1>S3; and the total setting percentages in S1, S2, and S3 of ZD958 were 44, 72, and 15 % respectively. The total floret number of tassel primordium differentiation, fertility rate, and seed setting rate of florets in S3 treatment was the minimum; kernels per ear decreased seriously and single ear setting percentage was only 16 %; although floret degeneration number of S2 during ear differentiation stages increased and floret fertility rate reduced than that of CK, fertilization flower seed production increased and abortive seed decreased after canceling shading. Aborted kernel of S1 increased and kernel dry weight reduced, resulting in a significant decrease of kernel number per ear and kernel weight, and the grain abortive rate of 40-62 %. In conclusion, shading changed the growth and development process and caused infertility of tassel and ear; tassel branches decreased, reducing pollen vitality and silks differentiation cut down; and grain dry matter accumulation and setting percentage decreased, causing yield reduction. Grain yield and biomass reduced 66, 36, and 93 % compared to the control by shading treatments of S1, S2, and S3, respectively. [ABSTRACT FROM AUTHOR]

Optimizing the canopy nitrogen (N) distribution by matching the available light resources to construct a light-N matching canopy structure of summer maize is important to improve yield and narrow the yield gap (YG). A field experiment with four integrated agronomic management practice systems [a control treatment (T1), an improved management system (T2), a super high-yield management system (T3), and an optimized management system (T4)] was conducted at Da Wenkou Town, Tai'an, China, from June to October in -2018–2020 to study the canopy light and N distribution and photosynthetic N use efficiency of summer maize. The results showed that optimized integrated agronomic management practices could coordinate canopy light and N distributions to increase the yield, thus narrowing the YG between T1 and yield potential by 1.9–5.2 Mg ha-1. In addition, the T4 treatment intercepted more radiation by adjusting the leaf area. Furthermore, the leaf N content of T4 in the middle canopy was significantly increased. The coordination of canopy light and N distributions of T4 was increased significantly, which was conducive to maximizing the use of N and solar radiation and increasing photosynthetic N use efficiency significantly by 9.4–41.4%, compared to that of T1. As a result, the yield of T4 was increased by 37.0% compared to that of T1. And T4 narrowed the YG by 3.4 Mg ha-1. Therefore, the T4 was the best choice for achieving a high-yield and high-efficiency production of summer maize in this study. • Optimized agronomic management improved leaf nitrogen vertical distribution. • Optimized agronomic management increased canopy light interception. • Optimized agronomic management narrowed yield gap by regulating canopy structure. [ABSTRACT FROM AUTHOR]

Abstract: Excessive nitrogen (N) fertilizer application, outdated fertilization techniques, and non-optimal planting patterns are current cultivation problems with summer maize (Zea mays L.) among smallholders in North China. To try to solve those problems, this study examined four integrated agronomic management treatments-MT (FP: traditional farming practices; OPT-1: an optimized combination of cropping systems and fertilizer treatment; HY: treatment based on high-yield studies; and OPT-2: further optimized combination of cropping systems and fertilizer treatment) and four N application rate treatments-NT (0, 129.0, 184.5, and 300.0kgha−1). Maize grain yield and N efficiency were determined under each treatment. Grain yield, yield components, individual/population dry matter weight, N partial factor productivity (PFPN), N use efficiency (NUE), and agronomic efficiency of N (AEN) were measured. Results from the NT revealed no significant increase in grain yield in response to N applied above 184.5kgha−1 and increased yield was achieved by the MT. In MT, the change in sowing method from relay intercropping to direct seeding was effective in avoiding maize rough dwarf virus and in encouraging mechanized production; individual and population dry matter accumulation from the tasseling stage (VT) to physiological maturity stage (R6) increased in response to delayed sowing date and harvesting time; grain yield increased significantly from more ears per hectare due to increased planting density; and high N efficiency was achieved after optimizing fertilization patterns. In this study, OPT-2 obtained 67.0%, 104.0%, and 53.5% higher grain yield, PFPN, and NUE, respectively, compared to FP, achieving high yield and high N efficiency. Furthermore, the low AEN value suggests that further reduction in the N application rate of OPT-2 may be possible. [Copyright &y& Elsevier]

• Controlled-release urea with irrigation affects maize biomass and N accumulation. • Optimum controlled-release urea improved photosynthetic capacity for each irrigation level. • The interaction of irrigation and controlled-release urea on maize yield was significant. Effective irrigation and nitrogen (N) management is crucial for sustainable agricultural development. Controlled-release fertilizer has been widely used to improve N use efficiency and save labor in one-off application. A specially designed soil column and field trial were conducted to investigate the effect of the interaction of irrigation management and nitrogen on yield, N uptake, and photosynthetic characteristics of summer maize. In the soil column experiment, severe water stress (W1) significantly decreased the leaf area index, relative chlorophyll content, and net photosynthesis and delayed maize growth, resulting in significant yield loss. Under mild water stress (W2), increased controlled-release urea (CRN) application counteracted the inhibition of maize growth. Under adequate water condition (W3), the yield and maize growth exhibited no significant difference between CRN 210 and 315 kg N ha–1. In the field experiment, CRN 210 and 315 kg N ha–1 also exhibited similar yield and were significantly higher than common urea 315 kg N ha–1 under conventional irrigation (CI). Under half-reduced conventional irrigation (RI), yields of CRN 315 kg N ha–1 increased by 10.5% and 7.5% compared with that of CRN 210 kg N ha–1 in 2014 and 2015. The interaction between irrigation and CRN could effectively alleviate the adverse effects of mild drought on summer maize by delaying leaf senescence, increasing chlorophyll content, and improving photosynthetic performance during the grain-filling period. These characteristics allowed more water and nutrients for maize plant and ultimately increased the yield. In areas with adequate irrigation conditions, CRN reduced to 210 kg N ha–1 could satisfy maize growth. In mild water stress and half-reduced conventional irrigation area, the CRN rate of 315 kg N ha–1 used by traditional farmers showed superior benefits. [ABSTRACT FROM AUTHOR]