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Article

Integrated Moderate Stay-Green Hybrids and Optimal Nitrogen Management Improving Maize Productivity and Grain Nitrogen Uptake

by
Yuewen Zhang
1,2,†,
Xiaoyang Zhang
1,2,†,
Xingbang Wang
1,2,†,
Fulin Zhao
1,2,
Yangping Xu
1,2,
Huaiyu Yang
1,2,* and
Wushuai Zhang
1,2,*
1
College of Resources and Environment, Southwest University, Chongqing 400715, China
2
Interdisciplinary Research Center for Agriculture Green Development in Yangtze River Basin, Southwest University, Chongqing 400715, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Agronomy 2025, 15(4), 853; https://doi.org/10.3390/agronomy15040853
Submission received: 18 February 2025 / Revised: 22 March 2025 / Accepted: 26 March 2025 / Published: 29 March 2025
(This article belongs to the Special Issue Exploring Mechanisms and Technologies for Enhancing Nitrogen Efficiency in Maize Production)
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Abstract

:
Investigating the interaction effect of nitrogen (N) management strategies and stay-green types of maize hybrids is essential for enhancing N use efficiency and developing N-efficient hybrids. A field experiment was conducted with five N management treatments (Control, Opt.N*70%, Opt.N, Opt.N*130%, and Con.N) and two stay-green types of maize hybrids (stay-green hybrids: DH605 and ZD958; moderate-green hybrids: XY335 and XY1266) to examine their interaction effects on maize yield, aboveground biomass, and N uptake and allocation. The highest grain yields for moderate stay-green and over stay-green maize hybrids were 12.8 Mg ha−1 and 10.8 Mg ha−1, respectively. Compared to over stay-green hybrids, moderate stay-green hybrids exhibited a significantly higher aboveground biomass and N uptake. Under an optimal N (Opt.N) treatment, moderate stay-green hybrids achieved a 15.8% higher grain yield than over stay-green hybrids. Under the Opt.N*130% treatment, moderate stay-green hybrids had the highest grain N concentration, averaging 13.1 g kg−1. Nitrogen application enhanced N allocation to grains, resulting in a 3.1–7.7% increase in grain N content. Moderate stay-green hybrids with optimal N management exhibited a 1.9% higher grain N content compared to over stay-green hybrids, whereas their vegetative organs had a relatively lower N content except for the Opt.N*130% treatment. Selecting a suitable maize hybrid (e.g., moderate stay-green maturity hybrid, XY335) and optimizing N fertilizer management can enhance grain yield, grain N content, and enhance N absorption and utilization efficiency.

1. Introduction

Maize (Zea mays L.) is the largest crop in China, accounting for 46% of the total planting area among three major grain crops [1]. Nitrogen (N) fertilizer is crucial for improving maize yield and N accumulation [2]. However, the over-application of N fertilizer can not only increase yield continually, but also lead to a waste of N resources [3,4]. The rational application of N fertilizer, which enhances N use efficiency and grain N content [5], is crucial for increasing maize productivity. Moreover, appropriate N-efficient hybrids produce more grain with lower N input and benefit sustainable maize production [6]. Over the previous decades, maize grain yield has steadily enhanced due to genetic and agronomic enhancements [7,8,9,10]. Thus, the exploration of a combination of rational N fertilizer management strategies and appropriate maize hybrids possesses both scientific and practical significance.
Theoretically, the ideal enhancement of maize grain yield depends on the synchronous improvement of the total dry matter accumulation [11] and harvest index [12]. This improvement can be obtained via selecting an appropriate hybrid with a higher biomass and higher partitioning ratio to the ear component, as well as a sufficient N supply during the whole growth stage. Consequently, studying the response of various stay-green maize types to different N management approaches has the potential to facilitate optimal hybrid and N fertilizer matching, thereby enhancing their synergistic effects [13]. Current studies primarily focus on the impact of N fertilizer management on grain yield [14], with limited studies examining the interaction between the N fertilizer application and different stay-green maize hybrids. The grain’s N originates from two primary sources, the direct absorption by roots post-flowering and the translocation of N stored in vegetative organs prior to flowering [15]. During the reproductive stage, proteins in vegetative organs undergo degradation and are translocated to other organs, serving as a N source for grain development [16]. Prior research indicated that the proportion of N stored in vegetative organs (e.g., stem and leaf) before flowering and after remobilization varied based on environmental conditions and genotypes [17]. This remobilized N comprises 45–65% of the total N in grains [18]. Maize must balance maintaining photosynthesis and the remobilization of N from leaves during the grain filling period after flowering, as N transfer and senescence occur simultaneously in its vegetative organs [19]. Research has shown that maize hybrids that possessed favorable traits simultaneously achieved high yields and efficiencies [20]. However, selecting the appropriate combination of precise N management and stay-green type by examining maize productivity performance remains a formidable challenge.
Maize is generally classified into standard and stay-green types based on leaf greenness in the harvest stage, and the green-mature type is further subdivided into moderate stay-green and over stay-green types [21]. A prior study indicated that standard maize exhibited a comprehensive N translocation to its reproductive organs during post-flowering stages; however, an accelerated leaf senescence in later stages results in insufficient photosynthetic products during the grain-filling period, ultimately leading to reduced grain yield [19]. Stay-green maize maintains a prolonged green leaf period during post-flowering stages, exhibits robust photosynthesis, and achieves a high grain yield. However, over stay-green maize retains higher residual N in its vegetative organs after maturity, leading to decreased N use efficiency [21]. Shao et al. [22] demonstrated that moderate stay-green maize hybrids achieved a N transfer efficiency of 57%, whereas over stay-green maize hybrids only reached 28%. Consequently, developing moderate stay-green hybrids is crucial for enhancing the yield and N use efficiency [23]. However, the mechanism, from an organ perspective, underlying both high productivity and high grain N accumulation resulting from an appropriate combination of N management and maize hybrids remains unclear.
In this study, we conducted a field experiment using two stay-green types of maize (with two hybrids each) and five N management models and analyzed the grain yield, accumulation, and distribution of the biomass and nitrogen among maize organs. Our objectives were (1) to explore the appropriate combination of precise N management and stay-green type by examining maize productivity performance; (2) to clarify the mechanism, from an organ perspective, underlying both high productivity and high grain N accumulation resulting from an appropriate combination of N management and maize hybrid selection. We believe this study will provide theoretical support for the breeding of innovative high-yield and high-efficiency maize hybrids.

2. Materials and Methods

2.1. Experimental Site

The field experiment was conducted at the High-Yield and High-Efficiency Modern Agriculture Demonstration Base of the Quzhou Experimental Station, affiliated with China Agricultural University (36.9° N, 115.0° E), Hebei province, China in 2019. This field experiment has been continued for 13 years until the year this study was conducted. The region has a typical temperate monsoon climate, featuring an average temperature of 26.0 °C during the maize season, mean annual precipitation of 437.6 mm, and annual sunshine duration of 2373 h. The typical cropping system in this region is winter wheat–summer maize rotation. The soil type is characterized as calcareous alluvial soil, and the initial basic physical and chemical properties in 0–30 cm soil depth were as follows: organic matter content of 12.6 g kg−1, total N of 0.83 g kg−1, available phosphorus of 7.2 mg kg−1, available potassium of 125 mg kg−1, a pH of 8.3, and bulk density of 1.36 g cm−3.

2.2. Experimental Design

The field experiment employed a two-factor split-plot design with four replicates. Within the main plots, five distinct nitrogen (N) management strategies were applied, while the subplots were utilized for testing four different hybrids. The dimensions of the main plots measured 15 m in width and 20 m in length, whereas the subplots were 5 m wide and 20 m long. The N treatments comprised the following: a control group with no N application (Control), an optimal N management (Opt.N) determined by in-season root zone N management (IRNM) as described by Chen et al. (2011) [24], 70% of the optimal management (Opt.N*70%), 130% of the optimal management (Opt.N*130%), and conventional N management following farmers’ practice (Con.N). In the Opt.N treatment, before planting, 45 kg ha−1 N was used. Between the 6-leaf (V6) and silking (VT) stages, as well as from VT to physiological maturity (R6), the Opt.N application management was determined by deducting the soil nitrate (NO3−-N) levels, as gauged within the root zone (0–60 cm depth for the V6 to VT phase and 0–90 cm for the VT to R6 phase), from the preset N targets of 185 kg ha−1 and 160 kg ha−1 for respective growth periods. Common urea was applied as N fertilizer in this experiment, with a N content of 46%, and its details for basal and topdressing are described in Table 1. Phosphorus fertilizer was applied in the form of superphosphate with 45 kg P2O5 ha−1, and 90 kg K2O ha−1 of potassium sulfate was applied as potassium fertilizer. Both phosphorus and potassium fertilizers were broadcasted to the soil before sowing along with urea. During the V6 and VT growth stages, urea was top-dressed through broadcast application.
These four maize hybrids were divided into two groups based on their stay-green types [21]: moderate stay-green (Xianyu 1266 and Xianyu 335) and over stay-green (Denghai 605 and Zhengdan 958). Xianyu 1266 (XY1266) and Xianyu 335 (XY335) were launched to the market by Pioneer Technology Co. (Beijing, China) in 2014 and 2015, respectively. Denghai 605 (DH605) is a widely grown commercial hybrid in China. Zhengdan 958 (ZD958) is currently the most popular high-yield hybrid employed in the study area [25,26]. The recommended planting density was 90,000 plants per hectare in the area [27]. Four hybrids were sowed on 10 June 2019. Except for the Control treatment, the R1 stage for XY1266 and XY335 occurred on 5 August and for DH605 and ZD958 on 7 August in the N treatments. However, in the Control treatment, due to N deficiency, silking was delayed to 7 August for XY1266 and XY335 and to 9 August for DH605 and ZD958. Harvesting took place at the R6 stage, marked by the appearance of the black layer, on 1 October for all four hybrids. Pesticides were used during the growing season only when necessary to prevent and treat diseases, weeds, and insects.

2.3. Sampling and Laboratory Procedures

At maturity (R6) stage, maize plants within an area of 12 m2 (5 m by 2.4 m, comprising four rows) in the center of each subplot were harvested by hand [23]. Subsequently, the cobs were dried to determine the grain yield. Grain yield was adjusted to standard grain yield (15.5% of water content). Maize plant samples were collected with five plants consecutively sampled from each subplot. These samples were subsequently divided into leaves (upper, lower, and ear leaves), stems (upper and lower stems, relative to the ear leaf), husks, cob, and grains to determine the total aboveground biomass and to analyze their N contents. Rows per ear and grains per row were manually counted to calculate grains per ear. After threshing, the grain weight of 1000 grains was measured in three replicates. All plant samples were dried to constant weight in an oven (HUYUEMING, Shanghai, China) at 70 °C and then sieved through a 1 mm sieve for subsequent laboratory chemical analysis. The nitrogen concentration of each tissue was determined using the Kjeldahl method [28].

2.4. Statistical Analysis

A two-way ANOVA (analysis of variance) model was employed, with N management strategies and maize hybrids as the factors, to evaluate the overall variability in grain yield, biomass, yield components, and N content. The least significant difference (LSD) test at the 0.05 probability level was utilized for post hoc comparisons. All statistical analyses were conducted using SPSS 21.0 software. Data processing and visualization were performed using Microsoft Excel 2019 and Origin 2021, respectively.

3. Results

3.1. Grain Yield and Yield Components

The nitrogen application significantly increased the maize mean grain yields of both stay-green types, by 87–125%, compared to the no N Control (Table 2). There were no further improvements observed with increased N management strategies, compared with the lowest N management strategy (Opt.N*70%) among the N application treatments. The moderate stay-green hybrid XY335 achieved the highest grain yield (12.8 Mg ha−1) under the Opt.N*70% treatment. The grain yield of each over stay-green maize hybrid was significantly lower than that of moderate stay-green maize hybrids under Opt.N*70% and Opt.N treatments. Under the Opt.N treatment, the moderate stay-green maize achieved a mean grain yield of 12.5 Mg ha−1, which was 15.8% higher than the mean of over stay-green types. In the relatively higher N management treatments (Opt.N*130% and Con.N), DH605 had the lowest grain yield among the four hybrids, and the grain yield of over stay-green maize ZD958 had no significant differences compared with the two moderate stay-green maize hybrids.
The nitrogen application significantly increased the rows per ear, grains per row, and grains per ear, compared to the Control (Table 2). There were no significant differences in these three parameters observed in the four N application treatments. The rows per ear of ZD958 was lowest in the Opt.N*130% treatment, and there were no differences among the hybrids in other N application treatments. The hybrid XY1266 achieved the highest grains per row in all N application treatments, which were significantly higher than those of the over stay-green hybrids. A similar trend was observed in the grains per ear. The N management treatments had no significant effect on the 1000-grain weight of both stay-green types of maize. The 1000-kernel weights of moderate-green mature hybrids were relatively higher than those in the moderate stay-green hybrids. The nitrogen application significantly increased the harvest index compared to the Control, and there was no significant difference among the N management strategies. ZD958 had the lowest harvest index under Opt.N*70%, and DH605 and XY335 had lower harvest indexes under Opt.N*130% compared to the other hybrids.

3.2. Biomass Accumulation and Distribution

The nitrogen supply enhanced the aboveground biomass of both moderate stay-green and over stay-green maize hybrids (Figure 1). There were no significant differences in the aboveground biomass among the four N management strategies. Under the treatments of Opt.N*70% and Opt.N, the aboveground biomass of each moderate stay-green maize hybrid was significantly higher than that of each over stay-green maize hybrid. The mean aboveground biomass of over stay-green maize hybrids under the Opt.N*70% treatment was 16.4 Mg·ha−1, which was substantially lower than the mean of the moderate stay-green maize hybrids (21.8 Mg·ha−1). Under the Opt.N treatment, the aboveground biomass of the moderate stay-green maize hybrids reached 21.5 Mg·ha−1, which was 20.6% higher than that of the over stay-green maize hybrids. The aboveground biomass of the over stay-green maize DH605 was the lowest under both the Opt.N*130% and Con.N treatments. In the relatively higher N management treatments (Opt.N*130% and Con.N), the aboveground biomass of over stay-green maize ZD958 had no significant differences compared with the two moderate stay-green maize hybrids.
The average distribution proportion of the biomass in various tissues, ranked from high to low, is as follows: grain > lower stem > upper leaf > upper stem > lower leaf > ear axe > husk > ear leaf. The nitrogen supply increased the proportion of maize grain in all aboveground tissues (Figure 2). The Opt.N treatment increased the percentage point of grain by 12.3 compared to the Control treatment. And similar trends were observed in other N application treatments. The average distribution percentage point of the biomass in the upper leaves of the moderate stay-green maize among all treatments is 1.9 higher than that of the over stay-green maize hybrids, and the lower leaves are 2.9 lower.

3.3. Nitrogen Concentration in Different Organs of Maize

The N concentrations in the grain, husks, upper leaf, upper stem, and lower stem of different stay-green types of maize were significantly increased in N application treatments compared to the Control (Table 3). The mean grain N concentration of the four maize hybrids was highest (13.1 g kg−1) in Opt.N*130%, which was significantly higher than the Control and Opt.N*70% treatments, and had no significant differences compared with the Opt.N and Con. treatments. The N concentration in the husks of ZD958 was the highest among the four maize hybrids in the N application treatments. The N concentration in the upper leaf statistically peaked at Opt.N*130%, with a 33.8% increase for moderate-green and a 37.6% increase for over stay-green maize compared to the Control, respectively. Under the Opt.N treatment, the N concentration in the upper leaf of each over stay-green maize hybrid was significantly higher than each moderate stay-green maize hybrid. The mean N concentration in the upper leaf of over stay-green maize hybrids was 6.64 g kg−1, which was 27.7% higher than that of the moderate stay-green maize hybrids. The N concentration in the upper stem was higher than the Control under Opt.N*70%, with a slight but not significant increase when further increasing the N management treatments. In the Opt.N and Con.N treatments, XY335 had the lowest N concentrations in the upper stem. The N concentrations of lower stems in the Opt.N*130% and Con.N treatments had no significant differences compared with the Opt.N treatment, while they were significantly higher than the Opt.N*70% and Control treatments. For the over stay-green maize hybrids, the mean N concentrations in the lower stems ranged from 1.82 g kg−1 to 5.60 g kg−1, while the moderate stay-green maize hybrids ranged from 1.99 g kg−1 to 4.57 g kg−1 under the five N management strategies.
The nitrogen application had no significant effects on the N concentrations of the cob, ear-leaf, and lower leaf of the maize. Among the four hybrids, DH605 achieved the highest N concentrations of the cob in all treatments. Except the Opt.N*70% treatment, the other over stay-green hybrid ZD958 had the lowest N concentrations of the cob. In the Opt.N treatment, the N concentration in the ear-leaf of each over stay-green maize hybrid was significantly higher than each of moderate stay-green maize hybrids. The mean N concentration in the ear-leaf of the over stay-green maize was 10.4 g kg−1, while that of the moderate stay-green maize hybrids was 7.02 g kg−1. For the lower leaf, the N concentrations of ZD958 were lowest among the four hybrids in the Control, Opt.N, and Opt.N*130% treatments. The N concentrations of the lower leaf among the four maize hybrids had no significant differences in the Opt.N*70% and Con.N treatments.

3.4. Aboveground N Content and N Allocation

The nitrogen application significantly increased the aboveground N content of different stay-green types (Figure 3). There was no significant difference among the four N application treatments. The mean aboveground N content was highest under the Opt.N treatment, with the mean for stay-green and moderate stay-green maize hybrids being 159 kg·ha−1 and 180 kg·ha−1, respectively. Under the Opt.N treatment, the aboveground N content of each moderate stay-green hybrid was significantly higher than each of the over stay-green hybrids. The moderate stay-green hybrids XY335 and XY1266 had no significant difference to each other in the four N application treatments, and were significantly higher than ZD958 in Opt.N*70% and DH605 in the Opt.N*130% and Con.N treatments.
After N was supplied, the two stay-green types of maize transferred higher proportions of N to the grain (Figure 4); the N allocation proportions to grain were increased by 3.1–7.7 percentage points. Except for the lower stem, the overall N allocation proportions in nutritional organs were decreased when the N management increased, and the proportion in each nutritional organ was reduced by 4–8%. The proportion of the aboveground N content in the lower stem increased when the N management increased. The reduction proportions in the upper leaf, cob, and ear-leaf were 0.9–1.3, 1.7–3.0, 1.2–1.5 percentage points, respectively. Except for the Opt.N×130% treatment, the mean N allocation proportions to the grain of two moderate stay-green hybrids (83.9%) were 1.9% higher than that of the two over stay-green hybrids (82.1%). The N allocation proportions to the upper leaf of moderate stay-green hybrids were consistently higher than that of the over stay-green hybrids in five treatments. Except for the upper leaf, moderate stay-green hybrids exhibit lower residual nitrogen in each nutritional organ compared to over stay-green hybrids in the four N application treatments.

4. Discussion

4.1. Effect of N Management on Yield and Yield Components of Different Stay-Green Types

The stay-green trait of maize affects post-silking N accumulation and remobilization [29]. In this study, moderate stay-green hybrids demonstrated higher yields across all N management strategies compared to the over stay-green hybrids, thus benefiting from the greater remobilization of N. This aligns with the findings of J.R. Kosgey et al. [30]—indicating that hybrids of ‘low stay-green’ rating remobilized more of their pre-silking leaf N to grain, and the grain N content was lower in hybrids with a ‘high stay-green’ rating, where in this study, ‘low’ and ‘high’ are equivalent to ‘moderate’ and ‘over’, respectively. The moderate stay-green hybrid XY335 further enhanced the yield stability under the Opt.N*70% management strategy. Moreover, under the Opt.N*70% treatment, XY335 achieved the highest partial factor productivity of N fertilizers (PFP-N) of 128 kg kg−1, indicating a 171% increase compared to the Con.N treatment (Table S1). This highlights the tremendous potential for reducing N application while maintaining yield stability, which holds significant implications for optimizing the use of expensive N fertilizers in maize production in the North China Plain. Therefore, the combined use of moderate stay-green hybrids with relatively lower N application rates could achieve a higher yield and return on investment (ROI) for local farmers.
The insensitivity of the maize yield and yield components to a 66.7% reduction in N application (Table 1) challenges the conventional paradigm of linear yield–N response relationships, suggesting a decoupling between N input and reproductive success in specific stay-green types. This phenomenon may be rooted in the luxury consumption threshold theory [31], whereas optimized N management strategies (e.g., Opt.N*70%) likely synchronize N availability with critical developmental windows (e.g., silking to grain filling), thereby improving source–sink coordination.
The nitrogen fertilizer did not have significant effects on grain weight but supported a higher number of grains, which in turn led to higher yields (Table 2). The absence of N effects on the 1000-grain weight contrasts with Noor’s findings [32], potentially reflecting genotypic differences in assimilate partitioning strategies. Over stay-green hybrids, despite a prolonged leaf functionality, prioritized vegetative N retention over remobilization—a vestige of their evolutionary adaptation to high-N environments. In contrast, moderate-green hybrids exhibit a ‘just-in-time’ N allocation strategy, channeling photosynthetic products and N reserves preferentially to developing grains through cytokinin-mediated delayed senescence [33]. This aligns with the metabolic scaling theory, where an optimized biomass allocation to upper leaves (3.1~7.7% increase) maximizes the light interception efficiency per unit of N invested, as described by the ‘leaf economic spectrum’ [34]. In previous studies, Messina et al. [35] proposed the concept of “reproductive resilience”, where greater reproductive resilience enhanced the kernels per ear and yield. In this study, stay-green hybrids demonstrated a higher grain yield and kernels per ear (Table 2), which was probably attributed to their stronger reproductive resilience [36]. The more grains per row of the maize ear in moderate-green types likely emerges from auxin-management-dependent floral initiation and reduced kernel abortion rates during early reproductive stages. Crucially, this trait is amplified under N optimization, indicating the epigenetic regulation of inflorescence architecture in response to N signaling—a frontier for future molecular investigations.

4.2. Effects of N Application on Aboveground Biomass and Distribution of Different Stay-Green Types of Maize

The maize grain yield results from a complex process involving biomass accumulation and distribution throughout growth [19]. In this study, N application significantly boosts the aboveground biomass of all tested hybrids (Figure 1), mainly by fulfilling the N demand during silking and grain-filling and by enhancing the photosynthetic capacity and assimilates accumulation. These assimilates, mainly carbohydrates, are crucial for grain development [37]. Some scientists argue that solely increasing the harvest index post-Green Revolution has limited potential [38], emphasizing the need for alternative strategies. A high-yielding maize study showed aboveground biomass was critical [39]. Thus, strategies must focus on enhancing biomass, including photosynthetic efficiency, leaf activity duration, and assimilate partitioning. In summary, a holistic approach to increase maize yield requires optimal N management, like balanced N fertilization, ensuring effective photosynthetic product accumulation and assimilate partitioning [37,38,39].
Our study found that the aboveground biomass in moderate stay-green maize was significantly higher than that in over stay-green maize hybrids (Figure 1), thereby favoring a higher yield formation. These findings are consistent with Noor’s experimental results [32], demonstrating that XY335 exhibited a higher biomass than ZD958. Specifically, the biomass allocation in the upper leaves of moderate stay-green maize hybrids surpassed that of over stay-green maize hybrids, whereas the lower leaves exhibited a relatively lower proportion of biomass. No significant differences were observed in the allocation of other vegetative organs (Figure 2). The results indicated that moderate stay-green maize hybrids allocated a greater proportion of biomass to their upper leaves compared to over stay-green maize hybrids. The strategic allocation and configuration of biomass in the lower leaves of moderate stay-green maize facilitated enhanced accumulation in the upper leaves, subsequently promoting photosynthesis and ultimately resulting in higher yields.

4.3. N Uptake and Allocation of Maize with Different Stay-Green Types Under Different N Management Treatments

This study demonstrated that N application increased both the N content and harvest index in aboveground maize, which was consistent with a previous study [40]. Within optimal N application management treatments, elevating the N supply significantly boosted grain N concentration [41]. However, beyond the optimal N management system, further N additions yielded only marginal, nonsignificant gains in grain N concentration, emphasizing the necessity of site-specific N management to balance yield and grain quality. Notably, moderate stay-green hybrids exhibited a higher N uptake compared to over stay-green types under N application, and were driven by their superior aboveground biomass production despite lower tissue N concentrations in vegetative organs. This paradox aligns with the ‘biomass dilution effect’ theory [42,43], where whole-plant N accumulation outweighs organ-level N concentration differences. Crucially, N partitioning strategies diverged between stay-green types: moderate stay-green hybrids prioritized N remobilization efficiency to grains, whereas over stay-green types accumulated more N in senescing vegetative organs (e.g., ear leaves and upper stems) at maturity. We attribute this disparity to the prolonged photosynthetic activity of ear leaves in moderate stay-green hybrids, which sustains post-anthesis N reallocation—a mechanism supported by Shao’s findings of 55% N remobilization efficiency in moderate stay-green hybrids versus 27% in over stay-green ones [22].
While previous studies focused predominantly on the grain N sink strength [44,45], our work reveals that the N application rate had no significant effect on N residue concentrations in the cob, ear leaves, or lower leaves. The lack of N response in lower leaves likely stems from their premature senescence, reallocating N to metabolically active sinks like ear leaves. These findings address a critical knowledge gap regarding post-harvest N residue dynamics across stay-green types, highlighting that moderate stay-green hybrids (e.g., XY335, XY1266) achieved an enhanced grain N sink capacity without a yield penalty—a synergistic advantage unobserved in over stay-green hybrids (e.g., DH605, ZD958). This underscores the potential of stay-green-driven ideotype selection to mitigate yield–N trade-offs in maize production systems.

5. Conclusions

This study highlights the critical interaction between N management strategies and maize stay-green types in shaping yield and N content. Moderate stay-green hybrids (e.g., XY335) demonstrated a superior yield and N content under optimized N management, with reduced nitrogen input, which is attributed to the enhanced biomass allocation to photosynthetically active upper leaves and the efficient nitrogen remobilization to grains. In contrast, stay-green hybrids retained more N in vegetative organs at maturity, showing lower adaptability under N reduction. These results emphasize the necessity of aligning hybrid stay-green types with precise N management strategies. The findings advance N-efficient maize breeding and precise fertilization practices by linking physiological traits to agronomic outcomes. The results suggest that local farmers should effectively maintain yield stability and enhance their ROI by adopting the moderate stay-green hybrid XY335 and further reducing nitrogen fertilizer application rates. Future work should unravel the genetic and physiological drivers of biomass partitioning and N translocation, while validating these dynamics across diverse environments to support scalable, sustainable maize production systems.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agronomy15040853/s1, Table S1: The partial factor productivity of nitrogen fertilizer (PFP-N) among treatments and hybrids.

Author Contributions

Conceptualization, Y.Z. and X.W.; methodology, X.Z. and F.Z.; software, X.W. and Y.X.; formal analysis, Y.Z. and X.Z.; investigation, X.Z., F.Z. and X.W.; resources, H.Y. and W.Z.; data curation, Y.X. and F.Z.; writing—original draft preparation, Y.Z. and Y.X.; writing—review and editing, Y.Z. and X.W.; supervision, H.Y. and W.Z.; project administration, H.Y. and W.Z.; funding acquisition, W.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Key Research and Development Program of China (2023YFD1900600, 2022YFD1901505) and the earmarked fund for China Agriculture Research System (CARS-02).

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

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Figure 1. The aboveground biomass of two stay-green types under different N management treatments. The two stay-green types are over stay-green types (DH605 and ZD958) and moderate stay-green types (XY335 and XY1266). The N management strategies included Control = no N; Opt.N*70% = 70% of optimal N; Opt.N = optimal N; Opt.N*130% = 130% of optimal N; and Con.N = conventional N management following farmers’ practice. The optimal N management was determined by the in-season root zone N management. The means followed by same letters are not significantly different among the four hybrids (lowercase) or five N management treatments (uppercase) at p < 0.05 according to the LSD.
Figure 1. The aboveground biomass of two stay-green types under different N management treatments. The two stay-green types are over stay-green types (DH605 and ZD958) and moderate stay-green types (XY335 and XY1266). The N management strategies included Control = no N; Opt.N*70% = 70% of optimal N; Opt.N = optimal N; Opt.N*130% = 130% of optimal N; and Con.N = conventional N management following farmers’ practice. The optimal N management was determined by the in-season root zone N management. The means followed by same letters are not significantly different among the four hybrids (lowercase) or five N management treatments (uppercase) at p < 0.05 according to the LSD.
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Figure 2. The aboveground biomass distribution of each hybrid under different N management treatments. The N management treatments included Control = no N; Opt.N*70% = 70% of optimal N; Opt.N = optimal N; Opt.N*130% = 130% of optimal N; and Con.N = conventional N management following farmers’ practice. The optimal N management was determined by the in-season root zone N management.
Figure 2. The aboveground biomass distribution of each hybrid under different N management treatments. The N management treatments included Control = no N; Opt.N*70% = 70% of optimal N; Opt.N = optimal N; Opt.N*130% = 130% of optimal N; and Con.N = conventional N management following farmers’ practice. The optimal N management was determined by the in-season root zone N management.
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Figure 3. The aboveground nitrogen content in each hybrid under different N management treatments. The N management treatments included Control = no N; Opt.N*70% = 70% of optimal N; Opt.N = optimal N; Opt.N*130% = 130% of optimal N; and Con.N = conventional N management following farmers’ practice. The optimal N management was determined by the in-season root zone N management. The means followed by same letters are not significantly different among the four hybrids (lowercase) or five N management strategies (uppercase) at p < 0.05 according to the LSD.
Figure 3. The aboveground nitrogen content in each hybrid under different N management treatments. The N management treatments included Control = no N; Opt.N*70% = 70% of optimal N; Opt.N = optimal N; Opt.N*130% = 130% of optimal N; and Con.N = conventional N management following farmers’ practice. The optimal N management was determined by the in-season root zone N management. The means followed by same letters are not significantly different among the four hybrids (lowercase) or five N management strategies (uppercase) at p < 0.05 according to the LSD.
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Figure 4. Aboveground nitrogen distribution of each hybrid under different N management treatments. N management treatments included Control = no N; Opt.N*70% = 70% of optimal N; Opt.N = optimal N; Opt.N*130% = 130% of optimal N; and Con.N = conventional N management following farmers’ practice. Optimal N management was determined by in-season root zone N management.
Figure 4. Aboveground nitrogen distribution of each hybrid under different N management treatments. N management treatments included Control = no N; Opt.N*70% = 70% of optimal N; Opt.N = optimal N; Opt.N*130% = 130% of optimal N; and Con.N = conventional N management following farmers’ practice. Optimal N management was determined by in-season root zone N management.
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Table 1. Fertilization amount and time of different nitrogen management treatments during maize season. N management strategies included Control = no N; Opt.N*70% = 70% of optimal N; Opt.N = optimal N; Opt.N*130% = 130% of optimal N; and Con.N = conventional N management following farmers’ practice. Optimal N management was determined by in-season root zone N management.
Table 1. Fertilization amount and time of different nitrogen management treatments during maize season. N management strategies included Control = no N; Opt.N*70% = 70% of optimal N; Opt.N = optimal N; Opt.N*130% = 130% of optimal N; and Con.N = conventional N management following farmers’ practice. Optimal N management was determined by in-season root zone N management.
TreatmentTotal Nitrogen Rate
(kg ha−1)		Pre-Sowing
(kg ha−1)		V6 Stage
(kg ha−1)		VT Stage
(kg ha−1)
Control0000
Opt.N*70%103.631.551.121.0
Opt.N14845.073.030.0
Opt.N*130%192.458.594.939.0
Con.N2501001500.0
Table 2. Grain yield and yield components of over stay-green and moderate stay-green maize hybrids under different N applications. N management treatments included Control = no N; Opt.N*70% = 70% of optimal N; Opt.N = optimal N; Opt.N*130% = 130% of optimal N; and Con.N = conventional N management following farmers’ practice. Optimal N management was determined by in-season root zone N management. Means followed by the same uppercase letter are not significantly different between five N management treatments, and the same lowercase letter were not significantly different between four hybrids at p < 0.05 according to LSD. ** and * indicate significant difference at p < 0.01, 0.05 levels, respectively, and NS indicate no significant difference.
Table 2. Grain yield and yield components of over stay-green and moderate stay-green maize hybrids under different N applications. N management treatments included Control = no N; Opt.N*70% = 70% of optimal N; Opt.N = optimal N; Opt.N*130% = 130% of optimal N; and Con.N = conventional N management following farmers’ practice. Optimal N management was determined by in-season root zone N management. Means followed by the same uppercase letter are not significantly different between five N management treatments, and the same lowercase letter were not significantly different between four hybrids at p < 0.05 according to LSD. ** and * indicate significant difference at p < 0.01, 0.05 levels, respectively, and NS indicate no significant difference.
TreatmentHybridGrain Yield (Mg ha−1)Grain Rows per EarGrains per RowGrains per Ear1000-Grain Weight (g)Harvest Index
ControlDH6055.41 ab B13.5 a B18.4 a B248 a B276 ab A0.46 ab B
ZD9584.33 c13.3 a15.8 b211 b262 b0.45 ab
XY12664.93 bc12.4 ab16.6 ab206 b280 a0.42 b
XY3356.41 a11.8 b18.7 a222 ab286 a0.49 a
Opt.N*70%DH6059.63 b A16.0 a A 25.7 c A411 b A281 b A0.57 a A
ZD9588.56 c14.5 a26.2 c380 c263 c0.53 b
XY126612.2 a14.7 a31.9 a468 a294 a0.58 a
XY33513.3 a14.7 a29.6 b435 ab313 a0.58 a
Opt.NDH60511.2 b A15.7 a A27.8 c A435 b A290 a A0.59 a A
ZD95810.3 b14.7 a26.2 c386 c290 a0.57 a
XY126612.9 a15.1 a33.9 a511 a285 a0.59 a
XY33512.1 a14.4 a31.4 b453 ab293 a0.57 a
Opt.N*130%DH6059.32 b A15.2 a A26.2 c A398 c A302 a A0.56 b A
ZD95811.8 a14.6 b29.8 b434 b270 b0.60 a
XY126613.2 a16.3 a32.8 a536 a279 ab0.60 a
XY33511.8 a15.0 ab29.0 bc435 b308 a0.56 b
Con.NDH6059.68 b A16.1 a A23.3 c A374 c A277 a A0.56 a A
ZD95810.5 ab15.4 a27.9 b430 b282 a0.57 a
XY126611.4 ab15.3 a31.8 a486 a276 a0.57 a
XY33511.8 a14.8 a29.4 ab436 ab306 a0.56 a
Variance analysis ANOVA
Hybrid (H) *****NSNS
Fertilizer Amount (F) ********NS*
H × F *NS**NSNS
Table 3. Nitrogen concentration in organs of different hybrids under different N management treatments. N management treatments included Control = no N; Opt.N*70% = 70% of optimal N; Opt.N = optimal N; Opt.N*130% = 130% of optimal N; and Con.N = conventional N management following farmers’ practice. Optimal N management was determined by in-season root zone N management. Means followed by the same uppercase letter are not significantly different between five N management treatments, and the same lowercase letter were not significantly different between four hybrids at p < 0.05 according to LSD. ** and * indicate significant difference at p < 0.01, 0.05 levels, respectively, and NS indicate no significant difference.
Table 3. Nitrogen concentration in organs of different hybrids under different N management treatments. N management treatments included Control = no N; Opt.N*70% = 70% of optimal N; Opt.N = optimal N; Opt.N*130% = 130% of optimal N; and Con.N = conventional N management following farmers’ practice. Optimal N management was determined by in-season root zone N management. Means followed by the same uppercase letter are not significantly different between five N management treatments, and the same lowercase letter were not significantly different between four hybrids at p < 0.05 according to LSD. ** and * indicate significant difference at p < 0.01, 0.05 levels, respectively, and NS indicate no significant difference.
TreatmentHybridg kg−1
GrainCobHusksEar LeafUpper LeafLower LeafUpper StemLower Stem
ControlDH60510.6 a C2.03 a A3.71 a B8.25 a A4.93 a B1.68 ab A0.87 a B1.75 a C
ZD95810.2 a 1.34 c3.26 a7.23 a4.65 a 1.34 b0.85 a1.89 a
XY126611.2 a 1.80 ab3.64 a7.74 a4.67 a1.80 a0.84 a2.08 a
XY33510.6 a 1.77 b2.99 a6.93 a4.47 a1.77 ab0.81 a1.90 a
Opt.N*70%DH60512.6 a B1.20 a A3.37 b A8.53 a A5.52 a A1.20 a A0.87 a AB3.25 b BC
ZD95812.3 a 1.18 a4.71 a9.31 a6.36 a1.18 a1.04 a4.35 a
XY126611.4 a 1.54 a3.60 ab8.14 a5.41 a1.54 a0.90 a2.73 b
XY33511.8 a 1.10 a3.52 b6.93 ab5.21 a1.37 a0.85 a3.00 b
Opt.NDH60513.5 a AB2.37 a A4.10 b A10.2 a A6.77 a A1.84 a A0.96 ab AB3.76 b AB
ZD95812.6 a 1.31 c5.16 a10.5 a6.52 a1.05 b1.07 a4.84 a
XY126612.2 a 1.57 bc3.77 b7.70 b5.30 b1.19 ab0.93 ab3.25 b
XY33512.6 a 1.69 ab4.19 ab6.35 b4.57 b1.41 ab0.82 b3.51 b
Opt.N*130%DH60514.3 a A1.69 a A4.18 ab A9.75 a A6.60 a A1.44 a A0.90 a A3.95 b A
ZD95812.5 b 0.92 b4.62 a9.93 a6.59 a0.86 b1.08 a5.52 a
XY126611.9 b 1.78 a4.18 ab6.97 a6.17 a1.78 ab0.93 a4.04 b
XY33513.5 ab 1.44 ab3.77 b7.87 a6.06 a1.44 a0.90 a4.10 b
Con.NDH60512.9 a AB2.37 a A4.38 a A9.36 ab A5.87 b A2.11 a A1.01 a A5.12 b A
ZD95812.9 a 1.31 b4.76 a11.0 a7.71 a1.31 a1.15 a6.07 a
XY126612.3 a 1.57 b3.65 b7.24 b5.69 b1.57 a1.01 a4.38 b
XY33512.9 a 1.69 ab3.76 ab7.45 b5.12 b1.69 a0.95 b4.75 b
Variance analysis ANOVA
Hybrid *****NS******
Fertilizer ****************
H × F NSNSNSNSNS**NS**
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Zhang, Y.; Zhang, X.; Wang, X.; Zhao, F.; Xu, Y.; Yang, H.; Zhang, W. Integrated Moderate Stay-Green Hybrids and Optimal Nitrogen Management Improving Maize Productivity and Grain Nitrogen Uptake. Agronomy 2025, 15, 853. https://doi.org/10.3390/agronomy15040853

AMA Style

Zhang Y, Zhang X, Wang X, Zhao F, Xu Y, Yang H, Zhang W. Integrated Moderate Stay-Green Hybrids and Optimal Nitrogen Management Improving Maize Productivity and Grain Nitrogen Uptake. Agronomy. 2025; 15(4):853. https://doi.org/10.3390/agronomy15040853

Chicago/Turabian Style

Zhang, Yuewen, Xiaoyang Zhang, Xingbang Wang, Fulin Zhao, Yangping Xu, Huaiyu Yang, and Wushuai Zhang. 2025. "Integrated Moderate Stay-Green Hybrids and Optimal Nitrogen Management Improving Maize Productivity and Grain Nitrogen Uptake" Agronomy 15, no. 4: 853. https://doi.org/10.3390/agronomy15040853

APA Style

Zhang, Y., Zhang, X., Wang, X., Zhao, F., Xu, Y., Yang, H., & Zhang, W. (2025). Integrated Moderate Stay-Green Hybrids and Optimal Nitrogen Management Improving Maize Productivity and Grain Nitrogen Uptake. Agronomy, 15(4), 853. https://doi.org/10.3390/agronomy15040853

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