Context: Long-term no-tillage causes soil compaction and reduces nitrogen (N) use efficiency in maize production in the North China Plain (NCP). Strip deep rotary tillage (ST), which loosens the intra-row soil to 40 cm while retaining inter-row nutrients, may overcome this limitation, but whether it can lower the optimal N rate for high maize yield remains unclear. Objective: This study evaluated whether strip deep rotary tillage (ST) could lower the optimal N rate required for high yield, relative to no-tillage (NT) and rotary tillage (RT). Methods: A 5-year field experiment (with data reported for 2022-2023) with four N application rates (0, 180, 240, and 360 kg N ha(-1)) and three tillage practices (no-tillage, NT; rotary tillage, RT; and strip deep rotary tillage, ST) was conducted to examine soil N availability, root-shoot coordination and yield formation. Results: Across four N rates, RT and ST increased maize yield by 12.3% and 17.9%, respectively, compared with NT. Notably, the optimal N rate for maximum yield shifted from 360 kg N ha(-1) under NT/RT to 240 kg N ha(-1) under ST. In the ST system with 240 kg N ha(-1) (ST-N2), soil bulk density decreased and soil porosity increased in the 20-40 cm intra-row soil layer, accompanied by higher mineral N content in the 0-50 cm soil profile. These changes were associated with improved root growth and greater post-silking N accumulation, which in turn increased leaf area index, dry matter accumulation, and root to shoot ratio at silking (R1) compared with NT and RT at equivalent or higher N rates. Nitrogen recovery efficiency (REN) and physiological efficiency (PEN) were also highest under ST-N2. Partial least squares path modeling (PLS-PM) identified root dry weight as the key hub linking soil improvements to yield gains. Conclusion and implications: In this NCP system, adopting strip deep rotary tillage allows a reduction in the optimal N rate from 360 to 240 kg N ha(-1) without sacrificing yield, providing an evidence-based option for reducing N fertilizer input while maintaining high maize yield in the NCP and similar agricultural regions.

Maize (Zea mays L.) is an important food crop worldwide. Understanding yield-limiting factors is essential for optimizing maize productivity under varying agroclimatic conditions. In this study, the relative contributions of climate, soil, and management factors to yield variation in spring and summer maize across 34 sites in China during 2017-2020 were assessed. Random forest (RF) models explained more than 80% of the yield variation, and SHapley Additive exPlanations (SHAP) and Accumulated Local Effects (ALE) were employed to interpret the effects of key variables. Climate emerged as the dominant driver, accounting for nearly 50% of the total feature importance. For spring maize, solar radiation during the establishment stage (ES) had a strong positive effect, whereas the minimum temperature during the grain-filling stage (GFS) had a negative effect. In contrast, summer maize yield was constrained by elevated nighttime temperatures during ES but benefited from increased growing degree days (GDD) during GFS. Among all the variables, planting density (PD) was consistently important across both systems, and increasing PD represented a direct and effective pathway to enhance yield. The results of the yield component analysis further revealed that the significantly higher kernel number per ear (on average 68 kernels more than summer maize) was the main contributor to the superior performance of spring maize. Climate scenario simulations indicated that, without adaptive management, future warming could reduce spring and summer maize yields by 6.1–11.8% and 5.5–9.1%, respectively. These findings underscore the stage-specific climate sensitivity of maize and support the development of targeted adaptation strategies to sustain yields under future climate change.

Optimizing sowing/harvest dates and tillage regimes can potentially balance grain yield and water use in the winter wheat–summer maize cropping system of the North China Plain (NCP), but their interactive effects remain poorly quantified. A three-year field experiment (2022–2024) was conducted with two cropping systems (traditional sowing/harvest dates, CK; optimized delayed dates, OD) and three tillage practices (no-tillage, NT; rotary tillage, RT; strip deep rotary tillage, ST) during the maize season. Results showed that OD shifted 4.9–5.6% of precipitation from wheat to maize season, increasing soil water depletion in wheat and recharge in maize, thereby expanding soil water storage capacity. ST significantly reduced bulk density in the 0–40 cm layer and increased deep-layer (40–200 cm) soil water content by 5.1–20.8%, enhancing groundwater recharge and reducing annual net groundwater use compared with RT and NT. Under OD+ST, summer maize yield increased, leading to 7.5–8.2% higher annual yield than CK+NT. This integrated practice also reduced soil evaporation and optimized crop transpiration, significantly improving annual water use efficiency (WUE). Principal component analysis confirmed that ST, especially when combined with OD, enhanced deep soil water replenishment and promoted water conversion into transpiration. We conclude that integrating delayed sowing/harvest dates with strip deep rotary tillage synergistically improves precipitation utilization, reduces groundwater depletion, and achieves high yield and WUE, providing a practical strategy for sustainable water management in the NCP and similar water-limited regions.

Soil compaction has become a serious limitation for further increasing the grain yield of maize (Zea mays L.) in the North China Plain (NCP). However, considerable variability exists among maize hybrids in their grain yield responses to soil compaction. To understand the physiological processes related to the variation of responses among maize hybrids to different soil compaction levels, a two-year field experiment was conducted with 17 maize hybrids and three soil compaction treatments (NC, no compaction with soil bulk density (SBD) of 1.0–1.3 g cm–3; MC, moderate compaction with SBD of 1.4–1.5 g cm–3, and HC, heavy compaction with SBD>1.6 g cm–3) to examine the root and shoot morphological traits, dry matter accumulation, and grain yield. Compared to NC, MC and HC significantly reduced the maize yield by 0.9–26.7% and 5.9–41.1% across the hybrids and years, respectively. Hybrids with high compaction tolerance (H) had greater grain yield than those with middle compaction tolerance (M) and low compaction tolerance (L), particularly under HC. The yield benefits obtained from the H hybrid were enhanced due to better root and shoot growth under HC conditions. Greater root length, root surface area, and root weight, as well as root activity, absorption capacity, and antioxidant capacity for H hybrid was found under HC conditions, and it also showed increased leaf area index and dry matter accumulation. Moreover, the increases in root growth indices for the H hybrid were greater than that of shoot growth, particularly under HC conditions, leading to a greater root/shoot ratio. We conclude that soil compaction impacts maize root and shoot growth differently depending on genotype, and the root growth advantages of the H hybrid were more obvious than shoot growth, which enhanced the yield benefits from the H hybrid under heavy compaction conditions.

Context or problem: In the Northeast China's intensive maize (Zea mays L.) production, reliance on high nitrogen (N) fertilizer inputs elevates risks of residual soil N and environmental losses, yet the long-term N fates remain unquantified. Split application of N fertilizer significantly enhances maize productivity and N use efficiency, but trade-offs between current season N losses and residual N accumulation of basal and topdressing fertilizers are poorly resolved across seasons. Objective or research question: The objectives of this study were to explore the fate of basal and topdressing N in maize production as affected by N application rates and hybrids, especially its distribution in the soil profile and contributions to grain yield. Methods: In this study, a three-year field experiment was conducted in Northeast China with five N rates (0, 100, 200, 300, 400 kg N ha(-1)) and two hybrids (XY335 and WK702). N fertilizers were applied in split applications before sowing (as basal N) and at nine-leaf stage (as topdressing N). The basal and topdressing N were labeled with N-15 in 2020, respectively, to trace the fate during the experimental years. Grain yield, N content of maize and N distribution in the soil profile were investigated in 2020-2022. Results: When N rate increased from 0 to 400 kg ha(-1), grain yield increased from 4.2 to 13.6 t ha(-1) in XY335 and from 4.3 to 12.4 t ha(-1) in WK702. XY335 increased grain yield by 8.3 %-14.3 % than WK702, especially under N rate of 200-400 kg ha(-1). The N-15 content of XY335 was higher than that of WK702 regardless of N rates and N sources. There was no significant difference in N-15 content of maize plant among N rates, except 100 kg ha(-1). In the first year, basal and topdressing N did not differ in content within maize plant regardless of N rates and hybrids. In subsequent years, the content of topdressing N was higher than that of basal N within plant, especially under higher N rates. Grain yields were positively correlated with basal and topdressing N, even when their magnitudes were small (less than 4 kg ha(-1)) in the third year. In term of N fate, basal N reduced N losses in the first year but increased soil residual N and subsequent N losses compared with topdressing N. WK702 reduced N losses by increasing soil residual N, although its plant N uptake was lower than that of XY335. The content of basal and topdressing N reduced with soil depth in the first two year while increasing in the third year. Basal N was higher than topdressing N regardless of soil layers, especially growing WK702. Grain yield exhibited a concave function with soil N content, where the soil N content corresponding to the maximum yield increased in the first two years but decreased in the third year with soil depth. Conclusions and implications: Basal N application significantly reduced seasonal N losses but increased residual N in the soil profile and subsequent N losses, especially under high N rates, compared with topdressing N. Moreover, maize genotypes enhanced the differences in N fate between basal and topdressing N. N-efficiency hybrid increased grain yield and N accumulation, while N-inefficiency hybrid reduced N losses via gains in soil residual N especially in the subsequent years. The findings of this study provide novel insights for optimizing N management to enhance maize N use efficiency and to mitigate N losses, thereby achieving sustainable agricultural development.

Appropriate tillage practice is essential for improving the production of maize (Zea mays L.) under various levels of soil compaction. This study aimed to reveal the underlying process of different tillage practices regulating maize root-shoot growth and yield response to various compaction levels. A two-year field experiment was conducted with two soil compaction levels (light compaction-LC, 1.45 g cm-3; heavy compaction-HC, 1.60 g cm-3) and three tillage practices (no-tillage-NT, rotary tillage-RT, and sub-soiling tillage-ST). HC decreased maize yield by 4.7-24.1 % compared to LC across tillage and years, meanwhile RT and ST significantly increased maize yield compared to NT under various compaction conditions. RT reduced soil bulk density and increased total porosity in the 0-20 cm soil layer compared to NT, while ST also contributed the effects in the 20-40 cm soil layer. As a result, ST exhibited an obvious advantage over RT in improving root length, root dry weight, and root absorption capacity, as well as shoot growth indices, such as photosynthetic parameters, leaf area index, and dry matter accumulation under HC, while it had no advantage under LC. Moreover, the improvement in root growth indices by ST was greater than that of shoot growth, particularly under HC, leading to increased root/shoot ratio. We concluded that both RT and ST could mitigate maize yield reduction from compaction by improving soil properties and root-shoot growth, while the effects of ST were enhanced under heavy compaction.

Context: Ethephon is used worldwide to improve the lodging resistance of maize, especially under high planting density, while limits grain formation. The mechanism of alleviating/eliminating the negative effects of ethephon on grain formation is still controversial. Objective: The purpose of this study was to improve the lodging resistance regulation scheme to explore the effects of combined application of ethephon and synergist on the photosynthetic performance and grain formation of maize population. Methods: Xianyu335 was used as the experimental material at two planting densities (low density, 67,500 plants ha-1, LD; high density, 97,500 plants ha-1, HD) and three chemical regulation modes (CK: clean water; ETH: spraying ethephon at 8th leaf stage; PHS: spraying ethephon at 8th leaf stage and spraying synergist at 11th leaf stage) at each planting density. The experiment assessed photosynthetic performance (chlorophyll, leaf area, net photosynthetic rate, etc.), dry matter, floret growth and development parameters, grain filling parameters, and yield. Results: Under LD conditions, PHS did not significantly increase grain yield. Under HD conditions without lodging, ETH yield decreased by 14.09 %, while PHS yield increased by 12.51 %; under HD conditions with lodging, ETH yield increased by 25.53 % and PHS yield increased by 40.28 %. PHS under HD reduced chlorophylldegrading enzyme activity and increased carbon assimilation key enzyme activity, resulting in 15.02 % and 60.18 % increases in chlorophyll content and net photosynthetic rate, respectively, which promoted dry matter accumulation at physiological maturity by 21.28 %. Moreover, PHS increased the number of fertilized florets by 6.01 % and reduced abortive grains 54.50 %, respectively, leading to a 14.75 % increase in grain number, compared with CK. At the same time, the leaf area index at physiological maturity increased by 29.66 % under PHS. This improvement led to a higher filling rate during the later stages of maize growth and extended the filling period by approximately 8.5 days. As a result, PHS increased grain weight by 6.62 % compared with CK. Conclusions: Compared with CK, PHS significantly enhances the net photosynthetic rate and delays leaf senescence, which increases the number and weight of grains while mitigating grain abortion driven by young ear growth and grain-filling, ultimately promoting grain yield of maize, especially under high planting density. Implications: PHS is a possible management method to achieve the common progress of lodging resistance and grain yield, which will be beneficial in promoting the further improvement of maize yield.

CONTEXT: Maize is crucial for global food security. China's Golden Maize Belt is a major maize production area. However, the sustainability of maize production in this region faces challenges from high nitrogen fertilizer application, low utilization efficiency, and severe nitrogen loss. The use of efficiency-enhanced nitrogen fertilizers, such as controlled-release fertilizer and that containing nitrification inhibitor etc. normally increases nitrogen use efficiency, yet this might have limited economic benefits due to high costs although its benefits in term of ecology and human health could be foreseen. OBJECTIVE: This study aimed to evaluate the environmental and economic impacts of efficiency-enhanced nitrogen fertilizers in maize production, further developing a policy framework for sustainable agriculture. METHODS: A split-plot field experiment was conducted with nitrogen fertilizer types as the main plots (including no nitrogen application, application of common urea and application of mixture with 50 % common urea and 50 % controlled-release urea), and nitrification inhibitor as the sub-plots (including no application and application of 3,4-dimethylpyrazole phosphate). Maize productivity, agronomic nitrogen use efficiency, nitrogen-saving potential, greenhouse gas emissions, and eco-economic benefits were measured. RESULTS AND CONCLUSIONS: The efficiency-enhanced nitrogen fertilizers significantly increased maize productivity by 3.1 %-11.4 % and agronomic nitrogen use efficiency by 7.3 %-26.8 % compared with common urea, with the controlled-release urea having a more prominent effect on grain yield. They also significantly reduced global warming potential by 11.0 %-24.7 % and greenhouse gas intensity by 10.2 %-29.1 %. However, the combined application of controlled-release urea and nitrification inhibitor had a subadditive effect on greenhouse gas mitigation. Addition of nitrification inhibitor leads to similar economic input (34.3 versus 34.5 $ ha-1) from the farmer, lower ecological premium paid by the government and the public (105.8 versus 151.0 $ ha-1), and a higher return on investment (4.2 versus 2.5) in maize production compared with controlled-release urea, which is therefore readily acceptable to all parties involved. Although the combined use of efficiency-enhanced nitrogen fertilizers brought ecological benefits of 248.9 $ ha-1, farmers needed economic support from the government and the public of 97.9 and 104.9 $ ha-1. SIGNIFICANCE: This study is novel in comprehensively quantifying the impacts of the efficiency-enhanced nitrogen fertilizers on maize production and greenhouse gas emission, and proposes a cost-sharing policy framework for sustainable agriculture.

Long-term excessive nitrogen (N) application neither increases nor enhances grain yield and N use efficiency (NUE) of maize, yet the mechanisms involving root morphological and physiological characteristics remain unclear. This study aimed to elucidate the mechanisms underlying stagnant grain yield under excessive N application by examining root morphological and physiological characteristics. A 10-year N fertilizer trial was conducted in Jilin Province, Northeast China, cultivating maize at three N fertilizer levels (zero N, N0; recommended N, N2; and high N level, N4) from 2019 to 2021. Two widely cultivated maize genotypes, 'Xianyu 335' (XY335) and 'Zhengdan 958' (ZD958), were evaluated. Grain yield, N content, root morphology, and physiological characteristics were analyzed to assess the relationships between N uptake, N utilization, plant growth, and root systems under different N treatments. Compared to N0, root biomass, post-silking N uptake, and grain yield improved significantly with increased N input, while no significant differences emerged between recommended N and high N. High N application enhanced root length and root surface area but decreased root activity (measured by TTC (2,3,5-triphenyltetrazolium chloride) method), nitrate reductase activity, and root activity absorbing area across genotypes. Root length and root to shoot ratio negatively affected N uptake (by-1.2 and-24.6%), while root surface area, root activity, nitrate reductase activity, and root activity absorbing area contributed positively. The interaction between cultivar and N application significantly influenced NUE. XY335 achieved the highest NUE (11.6%) and N recovery efficiency (18.4%) through superior root surface area (23.6%), root activity (12.5%), nitrate reductase activity (8.3%), and root activity absorbing area (6.9%) compared to other treatments. Recommended N application enhanced Post N uptake, NUE, and grain yield through improved root characteristics, while high N application failed to increase or decreased NUE by reducing these parameters. This study demonstrates that root surface area, root activity, nitrate reductase activity, and root activity absorbing area limit NUE increase under high N application.

Increasing planting density is a management option to improve maize (Zea mays L.) yield; however, soil compaction poses a challenge to this practice by adversely affecting maize growth. This study aimed to understand the physiological processes related to limitations in yield potential of densely planted maize from soil compaction. A two-year field experiment was conducted with two planting densities (low density—LD, high density—HD) and three soil compactions (no compaction—NC, 1.30 g cm−3, moderate compaction—MC, 1.45 g cm−3, and heavy compaction—HC, 1.60 g cm−3). Yield, root and shoot growth traits were measured during the maize growing season. Compared to LD, HD increased maize yield by 22.4–29.1

Context: Rainfed agriculture is crucial for global food security, with plastic film mulching a widely adopted practice in this domain. However, the impact of plastic film mulching varies significantly across different crop species. Objective and methods: This study conducted a comprehensive meta-analysis to evaluate the overall effects of plastic film mulching on the yield, water use efficiency (WUE), and nitrogen partial factor productivity (NPFP) of 13 different crop species. Results: Plastic film mulching significantly enhanced crop yield (26%), WUE (33%), and NPFP (26%) compared to non-mulched conditions. However, the promotional effects varied significantly among different crop species, with noteworthy improvements observed in soybean (44%, 41%, and 45%, respectively) and millet (42%, 57%, and 39%, respectively). For China 's major staple crops, plastic film mulching improved the yield, WUE, and NPFP of wheat (29%, 23%, and 27%, respectively), rice (12%, 36%, and 12%, respectively), maize (25%, 29%, and 26%, respectively), and potato (27%, 29%, and 27%, respectively). Regional suitability for plastic film mulching varied among different crops, with rice, maize, soybean, sunflower, linseed, and millet showing increased benefits in cold, semi -arid and arid areas (mean annual temperature (MAT) <= 10(degrees)C, mean annual precipitation (MAP) < 450 mm, and aridity index (AI) < 0.5). Conversely, peanut and wheat performed better in warm, moist and semi -humid regions (MAT > 10(degrees)C, MAP > 450 mm, and AI > 0.5). Moreover, nitrogen fertilizer application influenced the efficacy of plastic film mulching. For soybean, linseed, and millet, the optimal outcome of plastic mulching was observed under low nitrogen application ( <110 kg ha(-1)). For sorghum, sunflower, sweet potato, rice, peanut, potato, and wheat, the optimal outcome of plastic mulching was found under moderate nitrogen application (110 -220 kg ha(-1) ). As for maize, cotton, and oilseed rape, the optimal outcome of plastic mulching was observed under high nitrogen application ( >220 kg ha(-1)), but there was no significant difference between moderate and high nitrogen application. Conclusions: A tailored approach considering specific crop requirements and nitrogen application rates is essential for maximizing the benefits of plastic film mulching across diverse local conditions. Implications: This study offers valuable insights into optimizing crop productivity under plastic film mulching management systems.

Reasonable canopy structure and leaf physiological characteristics are considered as important factors for improving canopy nitrogen (N) distribution by matching the available light resources and thus increasing the grain yield of maize (Zea mays L.). However, the determinants of different maize varieties in light–N matching and grain yields with specific canopy structures and leaf physiological characteristics, as well as the response to the N application rate, remain poorly understood. In this study, we analyzed the relationships between different canopy structures and the enzyme activity and light utilization of spring maize in the field. Two maize varieties (XY335 and ZD958) with different canopy structures were used as the experimental material in a 2-year field experiment from 2014 to 2015, grown under different N inputs of 0, 100, 200, and 300 kg N ha−1 (N0, N1, N2, and N3) at a planting density of 90,000 plants ha−1 in Jilin Province on the Northeast China Plain. The results show that XY335 combined with N3 had a greater leaf angle, upper internode length and number, and upper leaf area index of the upper layer compared with ZD958. Higher N assimilatory enzyme (glutamine synthase (GS), glutamate synthase (GOGAT), and nitrate reductase (NR)) activities in the upper and middle leaves were observed in XY335 compared to ZD958. Furthermore, the light interception and light utilization efficiency of the upper leaves of XY335 increased, especially at higher N application rates, which significantly affected the N translocation post-silking and its distribution in different populations. As a result, the photosynthetic N use efficiency (PNUE) values of the upper leaves (10.4%) and middle leaves (5.2%) of XY335 were higher than those of ZD958, coordinating the canopy light and N distributions and being positively correlated with the maize grain yield. This suggested that the superior canopy structure of the upper layer and N assimilatory enzymes of the upper and middle leaves of this maize variety significantly increased the light interception of the canopy, while the synchronization of light and the N of the upper and middle leaves increased the light and N utilization efficiency of maize, which ultimately increased the grain yield at a high plant density.

To obtain high maize yield (Zea mays L.), nitrogen (N) fertilizer is widely used across the world and has greatly altered soil microbial communities and influenced soil health. Increasing plant density is an effective strategy for increasing maize yield, while variations in soil microbial communities in response to plant density under high N levels have not been well-studied. In Northeast China, maize was grown at low (LD, 67,500 plants ha-1) and high (HD, 90,000 plants ha-1) densities, combined with three N application rates of 0, 200, and 400 kg N ha- 1yr- 1(N0, N200 and N400). Based on a six-year field experiment, key soil microbial characteristics and physicochemical properties of top soils (0-20 cm), as well as yield and vegetative parameters were examined. Compared with that of LD, the maize grain yield of HD increased 10.8 % across N application rates from 2012 to 2017 (P < 0.05), while no significant differences between N200 and N400 were observed. HD significantly increased microbial biomass carbon (MBC), microbial biomass N (MBN), and bacterial and fungal diversity at N400 (P < 0.05). Dominant bacterial phyla across all samples were Proteobacteria, Acidobacteria, Actinobacteria and Thaumarchaeota, and fungal phyla were Ascomycota, Basidiomycota and Zygomycota. Species composition of HD shared more similarity between N200 and N400 than that of LD. HD significantly increased the abundance of Nitrososphaera and reduced the abundance of Pseudomonas and Sphingobium. From LD to HD, ammonia-oxidizing archaea (AOA) gene abundance increased while nirK gene abundance decreased at all N application rates, and ammonia oxidizing bacteria (AOB) and nirS gene abundances decreased at N0 and N400 but increased at N200 (P < 0.05). Shoot biomass and N uptake were positively correlated with MBC and MBN but negatively correlated with microbial community diversity. HD directly increased root biomass and N uptake, then reduced soil N contents (NH4+-N, NO3--N, and TN) and thus positively regulated soil microbial communities. Relative differences of diversity indexes and functional gene abundances between N application rates of HD were significantly lower than those of LD. Overall, our findings indicate that higher plant density of maize could mitigate the adverse effects of N fertilizer overuse on soil microbial communities, thus reconciling maize productivity and black soil health in Northeast China.

【Objective】Dense planting is one of the main measures to improve the high yield cultivation of maize, and density has a significant effect on the formation of maize starch. Therefore, this study analyzed the granule size distribution and viscosity parameters of different types of spring maize kernels under different increasing density conditions for improving the quality of maize starch. 【Method】 The field experiments were conducted at the Gongzhuling experimental base in Jilin province in 2019 and 2020.In the present experiments, eight main maize varieties in Northeast China, such as Xianyu 335, Zhengdan 958 and Nonghua 101, etc,were selected as experimental materials, and two planting densities of 67 500 and 97 500 plants/hm2 were set. The granule size distribution and viscosity parameters of starch in different treatments were measured by diffraction particle size analyzer and viscosity analyzer, and the relative quality of maize was measured by near-infrared analyzer, and the correlation analysis was conducted to clarify the effects of increasing density on the granule size distribution and viscosity parameters of endosperm starch in spring maize.【Result】The results showed that with the increase of planting density, maize grain yield and starch content increased significantly, and the increase of density significantly increased the volume, surface area and number percentage of large（＞17 μm）starch granules, while the opposite trend was observed in the volume, surface area and number percentage of small（＜3 μm） starch granules. It could be seen that with the increase of planting density, the volume and number percentage of small starch granules in maize kernels decreased significantly, and the volume and number percentage of large starch granules increased, indicating that increasing density was beneficial to the increase of the volume ratio of large starch granules, that is, increasing density promoted the accumulation of starch and increased the number of large starch granules and the formation of individual volume. At the same time, it was found that the peak viscosity, trough viscosity, breakdown and final viscosity of maize starch were significantly increased after increasing density. The results of correlation analysis showed that the starch content, yield and viscosity parameters of maize grain were negatively correlated with the volume percentage of small starch granules, significantly or extremely significantly negatively correlated with the volume percentage of medium（3-17 μm） starch granules, and significantly or extremely significantly positively correlated with large（＞17 μm） starch granules.【Conclusion】Increasing planting density could increase maize grain yield, starch content and its viscosity parameters by mainly affecting the granule size distribution of endosperm starch, namely increasing the proportion of large starch granules and reducing the proportion of small and medium-sized ones.

To explore the effects of drip irrigation modes on starch content and the activities of starch synthesis-related enzymes in spring maize at different grain positions in the irrigation area of the Xiliaohe Plain, the characteristics of starch accumulation and changes in the activities of adenosine diphosphate glucose pyrophosphorylase (AGPase), bound starch synthase (GBSS), and soluble starch synthase (SSS) at different grain positions were studied using ‘Nonghua 101’ as the test variety under mulch and shallow burial drip irrigation in 2019 and 2020. The results showed that the yield of shallow burial drip irrigation increased by 5.0% and 4.7% compared with mulch drip irrigation, and the 1000-grain weight increased by 7.4% and 6.9% from 2019 to 2020, in which grains in the middle ears improved by 7.7% and 4.1%, and in and upper ears by 10.8%, and 9.8%, respectively. The starch content, accumulation amount, and activities of synthesis-related enzymes of kernels located in different positions of spring maize ear were the lower part > the middle part > the upper part; the content and accumulation amount of starch under the two drip irrigation modes had little difference in the early stage, which were more advantageous in the upper part of the ear under shallow drip irrigation in the later growth stage. The activities of AGPase, GBSS, and SSS of shallowly buried drip irrigation were all higher than those of mulch drip irrigation in the late grain filling stage. The time to reach the maximum rate of starch accumulation in the middle and upper grains of the ear of the shallow burial drip irrigation was longer than that of the mulch drip irrigation, in which the active starch accumulation period was also longer, especially in the upper grains. The time to the maximum accumulation rate was delayed by 5.38 days, the average accumulation rate increased by 0.2836 mg·g−1·d −1, and the final starch accumulation increased by 16.6%. Path and correlation analysis showed that the time to reach the maximum rate, the average accumulation rate, and the maximum accumulation rate had a great influence on the final starch accumulation. Starch synthesis-related enzymes activities were significantly positively correlated with the starch accumulation rate, which showed that the activity of starch-related enzymes in the kernels located in the middle and upper parts of the ear at the late grain filling stage was strong under shallow drip irrigation. The active accumulation period of starch was also longer, the time for the accumulation to reach the maximum rate was delayed, and the average accumulation rate was high, which was one of the reasons for the increase in grain weight and yield under shallow drip irrigation compared with mulch drip irrigation.

Maize is the staple food of China, produced on 33.6% of the total arable land. In this context, an effective strategy to enhance maize yield is essential to meet the demand without expanding the cultivation areas. Maize yield can be increased by two key measures: plant-row space optimization and nutrient management. However, in traditional maize cultivation practices, fertilizer utilization by plants is inefficient. We therefore performed a manipulative experiment over two years (2018–2019), applying four treatments: (I) linear planting with nitrogen fertilization at 10 cm depth (CK), (II) linear planting with nitrogen fertilization at 20 cm depth (LD20), (III) zigzag planting with nitrogen fertilization at 10 cm depth (ZD10), and (IV) zigzag planting with nitrogen fertilization at 20 cm depth (ZD20). The aim of this study was to examine the influence of deep nitrogen fertilization and zigzag planting alone and in combination with root distribution, soil properties, canopy structures, and maize yield. Our results showed that all improved maize cultivating strategies (LD20, ZD10, and ZD20) increased the root length density up to 10–30 cm depth of soil layers compared to CK. Similarly, deep nitrogen fertilization increased the photosynthesis rate and leaf area duration after the silking stage. The leaf orientation value of the middle and upper canopies increased in zigzag planting compared to linear planting. It also increased the dry matter accumulation of medium leaves, leaf area duration, and dry matter accumulation after the silking stage. The maize yield was highly increased in ZD20 followed by ZD10, LD20, and the least by CK (traditional cultivating practices) in both years. Our study suggests that zigzag planting provides a higher yield than linear planting. Additionally, deep nitrogen fertilization in zigzag planting significantly increases the population resource utilization rate and yield by optimizing the root–canopy structures. Row spacing and nitrogen fertilization were found to be essential to enhance crop yield by influencing root growth and canopy efficiency.

Root morphology is an important factor determining nitrogen (N) uptake by plants, which might be affected by the extent of N application. The processes associated with root morphogenesis of spring maize in response to N application rates remain poorly understood. In this study, both field and pot experiments were conducted to explore the effect of zero-N (N0), optimized-N (N180), and high-N (N360) on root morphology, anatomical structure, and N accumulation in spring maize. N application rates affected root length and surface area, and its endogenous hormone contents. The largest difference in total root length and surface area among the three N rates was found at the silking stage: the total root length and surface increased by 51.36% and 42.58% under N180 and by 7.8% and 30.14% under N360, respectively, compared with N0, and the root/shoot ratio and root bleeding sap significantly increased under N180 and N360 compared with N0. The auxin and jasmonic acid levels of roots under N180 and N360 were higher than N0. N application rates also affected root microstructure and ultrastructure. Compared with N0, the proportions of root aerating tissue under N180 and N360 were decreased by 32.42% and 11.92% at silking. The root tip cell structure was damaged under N0, and intact under N180 and N360. Moreover, the 15 N allocation proportions to root and grain under N180 and N360 were increased compared to N0. Grain yields under N180 and N360 increased by 20.44% and 16.6% compared with N0, respectively. It can be concluded that optimized-N application decreased root aerated tissue and thus improved root length and root surface area through regulating auxin and jasmonic acid levels and affected N uptake and grain yield of N-efficient spring maize variety.

【Objective】The aim of this study was to explore the effects of different drip irrigation modes on starch accumulation and starch synthesis-related enzyme activities of spring maize, so as to provide a physiological basis for the understanding of the yield formation process in maize under the water-saving conditions.【Method】Using maize variety Nonghua 101 as the experimental material, a sub-plot design was selected for this experiment, and two irrigation modes were chosen as the main plot, including mulched drip irrigation (MDI) and shallow drip irrigation (SBDI), and the irrigation amount as the sub-plot included three irrigation levels (W1: 1 440 m3·hm-2; W2: 1 800 m3·hm-2; W3: 2 160 m3·hm-2, which equaled to the amount of 40%, 50% and 60% of the traditional irrigation, respectively). The amount and time of drip irrigation was conducted at the ratio of 1∶2∶2∶3∶2 for seedling stage to jointing stage, jointing stage to big bell mouth, big bell mouth to silking stage, silking stage to milk stage, and milk stage to harvest stage, respectively. The corn kernels were taken at every 7 days from 20 days after silking. The content of total starch in maize kernel was determined by acid hydrolysis DNS method. The starch synthase activity assay kit was used to determine the activity of adenosine diphosphate glucose pyro phosphorylase (ADPase), bound starch synthase (GBSS), and soluble starch synthase (SSS). On basis of that, the maize grain yield, characteristics of starch accumulation, and the changes enzyme activity of ADPase, GBSS and SSS were investigaged.【Result】There was no significant difference between effective panicle number and grain number per panicle of the two irrigation modes, and the 1000-grain weight and grain yield in shallow drip irrigation was lower than that of mulched drip irrigation under the treatment of W1, but no significant difference were found under the treatment of W2. The grain yield and 1000-grain weight in shallow drip irrigation were 5.7% and 8.4% higher in grain yield, and 11.9% and 12.1% higher in 1000-grain weight than that in mulched drip irrigation under treatment W3 in 2019 and 2020, respectively. The results of variance analysis showed that irrigation amount, drip irrigation mode and the interaction between irrigation amount and drip irrigation mode had a significant effects (P<0.01 or P<0.001) on 1000 grain weight, and the interaction between years, irrigation amount and drip irrigation mode had a significant effects (P<0.01 or P<0.001) on grain yield. Considering the content and accumulation of starch in grain, the shallow drip irrigation were both lower than that of mulched drip irrigation of W1, and W2 was lower than mulched drip irrigation in 20 days after silking, while no significant difference in 55 days after silking; W3 was lower than mulched drip irrigation in 41 days after silking, while higher than in 55 days after silking. Under the three irrigation amounts, the active accumulation period of starch in grain under shallow drip irrigation was longer than that of mulched drip irrigation, and the time for grain starch accumulation to reach the maximum rate was later than that of shallow drip irrigation. Active accumulation period of starch had the highest influence coefficient on the final accumulation of starch, then was the time of maximum rate. The starch accumulation rate in the late growth stage was highly correlated with the total starch accumulation in grains (P<0.001) and the yield (P<0.01). The activity of ADPase, GBSS and SSS in shallow drip irrigation were lower that of mulched drip irrigation in 20-27 d after silking, while the difference was reducing along with the maize growth; The three enzyme activity were higher under W3 than that of mulched drip irrigation at 48 days after silking, and also under W1 and W2 at 55 days after silking. Except no relationship of accumulation rate of grain starch and activity of ADPase under W1, the accumulation rate of grain starch showed a significantly positive relation with the activities of ADPase, GBSS and SSS under other treatments.【Conclusion】With the 60% of the traditional irrigation amount in shallow drip irrigation, it showed a higher activity of ADPase, GBSS and SSS at the late filling stage and a longer active starch accumulation period, also enhanced the ability of starch accumulation and increased 1000-grain weight, and possessed the highest maize grain yield. The shallow drip irrigation could increase the activity of the maize starch synthases, enhance the ability of starch accumulation, then increased grain weight and yield, and finally reached the purpose of water-saving and efficiency-improvement.

Soil total nitrogen is critical for crop productivity and related to agricultural managements. However, the effects of different fertilizer applications on soil total nitrogen storage are not well understood. To quantify soil total nitrogen storage under different fertilizer management practices and explore the effects of climate, soil texture, experimental duration, and cropping system on soil total nitrogen storage in China, we conducted a meta-analysis of 67 fertilizer management strategies from experiments conducted over a period of at least three years. This meta-analysis included 854 observations of changes in soil total nitrogen stock (TNS) under no fertilizer application (control, CK), chemical fertilization with nitrogen, phosphorus, and potassium (CF), CF plus straw retention (CFS), and CF plus manure addition (CFM) relative to initial soil TNS. The CFM and CFS treatments increased soil TNS, and the CFM treatments increased soil C/N ratio the most. The longer the experimental duration, the greater the increase in soil TNS in the CF, CFS, and CFM treatments. Soil texture and crop type significantly affected the changes in soil TNS. The experimental duration, initial soil TNS, soil C/N ratio, and cropping system had significant linear correlations with the change in soil TNS. Temperature and precipitation were not correlated with soil TNS. Results of random forest modeling indicated that the most important factor affecting changes in soil TNS was experimental duration (positive correlation), followed by initial soil TNS (negative correlation). The CFM treatments had the largest increase in soil TNS under various conditions. We recommend promoting CFM to improve soil fertility in farmlands globally.