Dual Benefits in Yield Enhancement and Grain Desiccation: Irrigation Coupled with Husk Removal Modulates Grain Moisture Dynamics in Maize

Abstract

Grain moisture influences grain number formation during the critical period as well as determining the final grain weight during the grain-filling period in maize (Zea mays L.). To clarify the relationships between grain number, grain weight, and grain moisture dynamics, a 2–year field experiment in a split-plot design was conducted with two irrigation treatments, well irrigation (WI) and no irrigation (NI), and with four husk removal treatments, including no husk removal as control (H₀) and removal of 1/4 (H_1/4), 2/4 (H_2/4), 3/4 (H_3/4), and 4/4 (H_4/4) of the husk layers, respectively. Husk removal reduced the maize grain number, grain dry weight, and yield, and the reductions were larger under no irrigation (33.4–33.5%) than under well irrigation conditions (27.7–33.2%). By contrast, irrigation increased grain water content by 11.1–13.4% and grain dry weight by 6.5–10.4%, regardless of husk removal. Meanwhile, the interactive effects between irrigation and husk removal were significant in grain water content but not in grain yield, reflecting the larger negative effects of husk removal on maize grain yield. In conclusion, husk plays a crucial role in grain number formation during the critical period and grain weight during the grain-filling period, especially in drought conditions, in relation to the trade-offs between yield enhancement and grain desiccation in maize production.

1. Introduction

As an important staple crop worldwide, maize serves as a source of food, animal feed, and bioenergy [1]. Maize yield depends on ear number, grain number, and grain weight, in relation to the genotype and environment [2,3,4]. In the context of climate change, sustainable and efficient water use has become a critical challenge for maize production. The increasing frequency of extreme drought events and erratic rainfall patterns threaten global food security by exacerbating water scarcity in agricultural systems [5]. The grain weight of maize depends on the grain-filling rate and duration, which are determined by the content and concentration of grain water [6].

Grain water status determines grain number and potential grain weight during the critical period in maize (~15 d before silking to ~15 d after silking). Developing climate-resilient strategies that optimize water allocation during this sensitive phase is essential for maintaining yield stability under fluctuating environmental conditions [7]. Grain dry matter accumulation is accompanied by the dynamics of grain water content during the grain-filling period [6,8]. Grain dry weight grows in an S–shaped curve, and grain water content first increases and then decreases until the harvest [9]. The grain-filling rate is closely related to the sink size and sink activity [10,11,12], which is closely related to the maximum grain water content [13]. Grain water concentration also determines the grain-filling duration [5,6]. These physiological linkages highlight the urgent need to reconcile irrigation management with crop architectural adaptations for improved water productivity. As such, water deficit during grain-filling period limits grain filling, even if a large sink capacity is established during the critical period [9,14].

The grain water content of maize depends on the hybrid and growth stage, which is also affected by the external environment, such as air humidity, soil moisture, temperature, and wind speed [12,15]. Climate change amplifies these environmental stressors, necessitating integrated approaches that combine controlled irrigation with protective agronomic practices [16]. Drought impairs grain growth and development, and reduces the transport of assimilates to ear, which reduces grain yield by about 20–48% [14,17]. Further analysis suggests that drought has a directly negative effect on grain water status, which restricts the metabolism of assimilates and reduces the grain-filling rate and duration [16,18,19,20,21]. Irrigation effectively improves the grain-filling rate and duration compared with drought, and increases the grain dry weight and yield [22]. However, excessive reliance on irrigation conflicts with sustainable water resource management, particularly in arid and semi-arid regions. This underscores the need to explore synergistic interactions between limited irrigation and crop morphological modifications.

Ear husk can maintain adequate moisture and temperature conditions for the developing ear, and is an important storage of assimilate [23,24]. Moreover, the number, length, and tightness of husk are related to the grain water content [25]. Modifying husk architecture presents a promising avenue for reducing crop water demand while preserving yield potential, which is a key consideration for climate-adaptive cultivation. Husk removal increases the evaporation from grain and reduces the grain water content at harvest, which facilitates mechanized harvesting and grain storage [12]. However, husk removal also reduces grain yield.

While there are many studies focusing on the relationship between grain water status and grain growth [8,12,14], fewer focus on the effects of irrigation and husk on grain yield in the context of climate-driven water constraints. The main objectives of this study were to explore (I) the response of grain water status to husk removal and irrigation, and (II) the interactive effects between irrigation and husk removal on the grain set and grain yield of maize. By investigating these interactions, this research aims to reveal the associated physiological mechanisms and to establish a framework for the dual optimization of water-use efficiency and maize productivity in the context of climate change. The hypothesis is that the combination of irrigation and husk removal balances yield enhancement and grain desiccation, thereby enhancing maize productivity, which addresses the competing demands of yield security and water conservation in changing climates.

2. Materials and Methods

2.1. Experimental Conditions and Treatments

Experiments were performed during maize growing seasons in 2019 and 2020 at Wuqiao Experimental Station of China Agricultural University (37°41′ N, 116°38′ E), Hebei, China. This region has a temperate continental monsoon climate with an average air temperature of 13.3 °C. The soil is a brown loam classified as Chromic Luvisol. Irrigation utilizes shallow groundwater. Daily temperature and precipitation during the maize growth season are shown in Figure 1, and the dates were obtained from a local meteorological station.

Maize hybrid Zhengdan958 (Zheng58 × Chang7-2, without husk leaves) was sown on 30 April 2019 and 26 April 2020 at a plant density of 67,500 plant ha⁻¹. The accumulated temperature requirement to reach physiological maturity for this hybrid is 3081 °C d. The experiment was in a split-plot design with irrigation treatment as the main factor and husk removal as the second factor, including three replicates. Each experimental plot was 21 m² (3 m wide by 7 m long) in size and consisted of five rows of maize spaced 0.6 m apart. Two irrigation treatments were conducted: well irrigation as WI and no irrigation as NI. Irrigation treatment was applied at the blister stage (around 12 days after the silking stage, some starch begins to accumulate in the endosperm) and the irrigation amount was controlled by a water meter at 45 mm each time. The irrigation dates were 13 July, 19 July, and 28 July in 2019 and 11 July, 18 July, and 26 July in 2020 (Figure 1). To prevent water and nutrient transfer, well irrigation and no irrigation were separated by a width of 1.5 m. Five husk removal treatments were conducted: no husk removal as H₀, removing 1/4 of the husk layers as H_1/4, removing 2/4 of the husk layers as H_2/4, removing 3/4 of the husk layers as H_3/4, and removing 4/4 of the husk layers as H_4/4. At the blister stage, husks were carefully peeled down from the top of the ear and then cut off with scissors from the bottom of the ear (Figure 2), during which the ear leaf, ear, and ear shank were not damaged. Efficient nutrient management was adopted in the field. Diseases, pests, and weeds were well controlled by fungicides, pesticides, and herbicides, respectively, during the experiment.

2.2. Plant Sampling and Trait Analysis

The silking time (i.e., when the first silks are visible) of maize was recorded, and plants with the same silking time were labeled. To determine the grain-filling characteristics, three marked ears were sampled from the 5th day after pollination to harvest at 3-day intervals in 2019 and 5-day intervals in 2020. The sampled ears were rapidly enclosed in an airtight plastic bag to prevent water loss. The middle grains of the ear were taken and mixed with tweezers in the lab. Afterwards, six 100-grain samples were selected from the collected grains in each treatment. The grain fresh weight was measured immediately, and the fresh grains were oven-dried at 75 °C to a constant weight to determine the grain dry weight. Water content was calculated by subtracting grain dry weight from grain fresh weight.

The grain-filling process was fitted by the logistic equation (Equation (1)), where W represents the hundred-grain dry weight (g), k represents the ultimate growth mass, a represents the primary parameter, b represents the growth rate parameter, and t represents the accumulated thermal time after silking (°Cd, the base temperature for maize is 10 °C and the day of silking is regarded as t = 0), respectively. The thermal time at the maximum grain-filling rate (Tm, Equation (2)), hundred-grain weight at the maximum grain-filling rate (Wm, Equation (3)), and maximum grain-filling rate (Gm, Equation (4)) were calculated as follows:

$$W=\left({\displaystyle \frac{k}{1+a{e}^{-bt}}}\right)$$

(1)

$$T_m={\displaystyle \frac{\mathit{ln}a}{b}}$$

(2)

$$W_m={\displaystyle \frac{k}{2}}$$

(3)

$$G_m={bW}_m\left(1-{\displaystyle \frac{W_m}{k}}\right)$$

(4)

In order to better describe how grain water content affects grain filling under husk removal, we referred to method [6] and used a bilinear model to fit the dynamic changes of grain water content (Equation (5)). Also, in order to highlight the relationship between grain water content and grain dry weight, we simulated the dynamic change of grain dry weight again using the broken stick model (Equation (6)), which fitted well to both grain water content and grain dry weight, and produced meaningful parameters.

$$WC=\left[\begin{array}{c}d+et \mathrm{f}\mathrm{o}\mathrm{r} t \le \mathrm{t}\mathrm{h}\mathrm{e}\mathrm{r}\mathrm{m}\mathrm{a}\mathrm{l} \mathrm{t}\mathrm{i}\mathrm{m}\mathrm{e} \mathrm{a}\mathrm{t} MWC \left(TTM\right)\\ d+eTTM-g\left(t-TTM\right) \mathrm{f}\mathrm{o}\mathrm{r} t>TTM \end{array}\right.$$

(5)

$$W=\left[\begin{array}{c}h+i\left(t-GFD\right) \mathrm{f}\mathrm{o}\mathrm{r} t \le \mathrm{g}\mathrm{r}\mathrm{a}\mathrm{i}\mathrm{n} \mathrm{f}\mathrm{i}\mathrm{l}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{g} \mathrm{d}\mathrm{u}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n} \left(GFD\right)\\ h \mathrm{f}\mathrm{o}\mathrm{r} t>GFD \end{array}\right.$$

(6)

where d represents the Y–intercept (g), e represents the initial rate of grain water accumulation (g °Cd⁻¹), and t represents the accumulated thermal time after silking. MWC represents the maximum water content, g represents the rate of water loss from MWC to physiological maturity (g °Cd⁻¹), h represents the ultimate growth mass (g), and i represents the grain growth rate during the effective grain-filling period (g °Cd⁻¹). The dry matter weight at MWC (DMM), grain growth rate before MWC (GBM), and grain growth rate after MWC (GAM) were calculated as the derivative of Equations (5) and (6).

At maturity, 20 ears were randomly harvested from each plot to determine the yield and ear traits. The grain number per ear (GN) was determined by calculating the number of grain rows per ear and the number of grains per row. Both yield and grain weight were expressed in terms of 14% standard moisture. Ear length was the axial distance from the tip to the bottom of ear. The ear barren tip length was the axial distance from the tip to the topmost grain.

2.3. Statistics

The grain yield and relevant grain parameters were analyzed with the analysis of variance (ANOVA) procedure using the general linear mode after the test of normality and homogeneity of variances with SPSS 18.0 (SPSS Inc., Chicago, IL, USA). The differences were compared with Duncan’s multiple range tests at the 0.05 probability level. SPSS 18.0 was used to analyze the correlation and path coefficients of the grain yield and grain related parameters. Sigma Plot 12.5 (Systat Software Inc., San Jose, CA, USA) was used to fit the grain-filling process and the dynamics of grain water content and dry weight. Figures were produced with Sigma Plot 12.5. Spearman correlation coefficient analysis was adopted for the correlation analysis, and the analysis diagram was drawn in R-Project (version 4.5.0) and RStudio (version 2024.12.1+563).

3. Results

3.1. Grain-Filling Characteristics

The dynamics of hundred-grain dry weight with thermal time are shown in Figure 3. Both no irrigation and husk removal slowed down the grain-filling process for maize. On average, across all husk removal treatments, no irrigation reduced the hundred-grain weight at maximum grain-filling rate (Wm), and the maximum grain-filling rate (Gm) decreased by 5.1% and 5.3% in 2019, and 7.9% and 9.8% in 2020, compared to well irrigation (Table S1). Likely, on average across the two water treatments, husk removal slowed the grain-filling process and reduced the Wm by 8.6–24.3% in 2019 and 8.6–25.5% in 2020. Gm of removing 1/4 of the husk layers (H_1/4), removing 2/4 of the husk layers (H_2/4), removing 3/4 of the husk layers (H_3/4), and removing 4/4 of the husk layers (H_4/4) decreased by 7.6%, 12.3%, 16.1%, and 21.1%, respectively, in 2019 and by 7.2%, 9.5%, 13.6%, and 19.5% in 2020, compared to H₀.

The broken stick model was used to fit the dynamics of hundred-grain dry weight and a bilinear model was used to fit the dynamics of grain water content (Figure 4). Hundred-grain dry weight first increased linearly with the thermal time and then remained at a stable level. On average, husk removal reduced the entire grain-filling duration by about 2–10%. Grain water content increased rapidly at first and then decreased slowly with a significantly smaller maximum grain water content in two years. The interaction of year, irrigation, and husk removal had significant effects on the grain water content (

Table 1. Two-way ANOVA test analyzing the effect of year, irrigation, and husk and their interactions on grain- and yield-related parameters.

Indicator (Sample Size)	Year (Y)	Irrigation (I)	Husk (H)	Y × I	Y × H	I × H	Y × I × H
Grain water content (720)	** 1	**	**	NS	**	**	NS
Grain dry weight (720)	NS	*	**	NS	NS	NS	NS
Ear length (60)	*	*	NS	*	NS	NS	NS
Grain number (60)	**	**	**	*	NS	NS	NS
Thousand-grain weight (60)	**	**	**	NS	*	NS	**
Grain yield (60)	**	**	**	NS	NS	NS	NS

Note: ¹ NS indicates no significance at 0.05 level, and * and ** indicate significance at 0.05 and 0.01 levels, respectively.

). The thermal time after silking was 240.6 °Cd and 314.4 °Cd, respectively, in 2019 and 2020 when the maximum water content (MWC) appeared in no irrigation treatment, 20–25 °Cd smaller than in well irrigation treatments. The MWC of no irrigation decreased by 14.2% and 9.9% in 2019 and 2020, respectively, compared to well irrigation. Correspondingly, the grain dry weight at MWC decreased by 21.5% in 2019 and 11.9% in 2020, and the grain growth rate before and after MWC also decreased by 15.1% and 5.6% in 2019 and by 11.7% and 8.9% in 2020, respectively (Figure 4 and Table S2). No irrigation increased grain water concentration at MWC in 2019 and 2020 (Table S3). Compared with H₀, husk removal significantly reduced MWC, with H_4/4 exhibiting the largest reductions in both years (24.5% in 2019 and 22.3% in 2020). The grain growth rate before MWC (GBM) reduced by 7.8–25.9% in 2019 and 5.6–17.7% in 2020, compared to H₀. The grain growth rates after MWC (GAM) in husk removal treatments were also significantly smaller than that in H₀ (Table S2).

3.2. Grain Yield and Its Components

The grain yields of maize varied significantly under well irrigation and no irrigation conditions, and the average grain yield of no irrigation decreased by 13.8% and 10.5%, respectively, compared to well irrigation in 2019 and 2020 (Figure 5A). In well irrigation, on average the grain yield of husk removal decreased by 8.4–27.9% in 2019, and 7.9–33.0% in 2020, compared to no husk removal (H₀), respectively. In no irrigation, on average the grain yield of husk removal decreased by 7.2–33.0% in 2019 and by 8.1–33.8% in 2020. Year, irrigation, and husk removal had significant effects on grain yield. However, the interaction of year, irrigation, and husk removal had no significant effects on grain yield (Table 1).

On average, across all husk removal treatments, the grain number (GN) and thousand-grain weight (GW) of no irrigation decreased by 9.4% and 6.0% in 2019 and 5.2% and 4.3% in 2020 compared to well irrigation, respectively (Figure 5C,D). In well irrigation, the GN of husk removal was 1.7–7.5% lower than that of H₀ in 2019 and 3.3–17.5% lower than that of H₀ in 2020. The GW of husk removal decreased by 3.1–18.3% in 2019 and by 3.4–15.5% in 2020, with H_4/4 exhibiting the largest reductions. In no irrigation conditions, the GN of husk removal was 4.1–15.9% and lower than that of H₀ in 2019 and 3.8–16.9% lower than that of H₀ in 2020. The GW of husk removal decreased by 1.0–20.4% in 2019 and by 4.5–18.0% in 2020. Year, irrigation, and husk removal all had significant effects on GN and GW (Table 1). However, the interaction of year, irrigation, and husk removal had no significant effect on GN. Husk removal increased the barren tip length, and husk removal had no significant effect on ear length (Figure 5B).

3.3. Relationship Between Grain Water Content, Grain Dry Weight, and Yield

The path coefficient analysis quantified the contributions of GBM and GAM to GW (Figure 6). GBM contributed significantly to GW (p = 0.609 *) under well irrigation conditions and GAM contributed significantly to GW (p = 0.554 *) under no irrigation conditions. Grain filling ended when the grain water content reduced to 32.5%, and grain water reduction was significantly correlated with grain dry weight reduction. Furthermore, yield reductions were significantly negatively correlated to the difference between GBM and GAM (Figure 7).

During the early grain-filling period, grain water content (GWC) was significantly positively correlated with the GN and GW, with the correlation coefficient ranging from 0.701 to 0.989 (p < 0.05) (Figure 8). GW was significantly positively correlated with the thermal time at the maximum grain-filling rate (Tm), Wm, Gm, MWC, GBM, and GAM (Figure 9). GBM and GAM had significantly positive correlations with MWC (p < 0.001).

4. Discussion

Husk removal reduced the maize grain number, grain dry weight, and yield, and the reductions were larger under no irrigation (33.4–33.5%) compared with under well irrigation conditions (27.7–33.2%), reflecting the importance of husk in yield formation, especially under drought conditions. There was a significant interaction between irrigation and husk removal on grain water content, but not on grain yield. These findings underscore the vulnerability of maize production systems to water scarcity, which is exacerbated by climate change. In drought-prone environments, protective husk structures can mitigate this vulnerability by regulating a more humid microclimate around the ear, thereby serving as a natural buffer against moisture loss [6,17,26].

Final grain weight is mainly determined by the grain-filling rate and duration [26,27]. In these two processes, grain water plays an important role [6,12]. In this study, husk removal reduced the grain water content and accelerated grain water loss in the late grain-filling period, thus reducing the grain-filling rate and duration. Grain filling stopped when the grain water content was less than 32.5% (Figure 4), which was consistent with the previous studies [6,8,12]. In contrast, irrigation increased the grain water content and grain-filling rate. This thus highlights the dual role of water management and husk removal in modulating grain water dynamics and ultimately yield formation in water-limited environments. Implementing targeted irrigation during the critical period and grain-filling stage mitigates maize yield losses, while minimizing husk disturbance in drought-prone areas reduces dependency on supplemental water inputs. This integrated approach improves sustainable water use under erratic rainfall regimes. Gambín et al. [6] also demonstrate that grain-filling duration mainly depends on the rate of water loss and biomass deposition rather than the time at which grain reached the maximum water content. A lower grain water content reduces grain weight mainly by reducing the grain growth rate before the maximum water content.

Grain development is related to grain water content at various growth stages [6,13]. Thus, the contribution of grain-filling rate to yield is dependent on the growth stage. The period from silking to maximum water content is about 16–22 days, which is a crucial process for grain formation [7,28]. In the context of climate change, rising temperatures and prolonged dry spells compress the effective grain-filling period. This shortening directly increases the demand for precision irrigation scheduling to optimize water availability during this critical, time-constrained window. Endosperm cells proliferate and enrich rapidly in this period, and determine the potential grain weight [26,29]. In this study, yield was largely explained by the grain growth rate before the maximum water content [30]. Furthermore, grain formation is closely related to the allocation of assimilates to the grain in maize [7]. Husk removal decreased dry matter accumulation by 20.0% and 19.8%, respectively, with and without irrigation (Figure S1). The grain-filling rate is also expected to be an important index in determining grain weight during the early grain-filling period (Figure 4). The early period of grain filling is within 14 days after silking, which affects the subsequent filling rate and potential grain weight [2,6,8]. This is sensitive to environmental factors or agronomic practices, such as irrigation and husk removal in this study. The sensitivity of early grain filling to water stress aligns with climate projections emphasizing the need for adaptive practices that stabilize early-stage development under variable precipitation [30,31].

Our results further imply that integrating husk management with deficit irrigation could enhance water productivity. Moderating husk removal intensity balances grain desiccation needs with yield protection, thereby achieving efficient water use without compromising productivity. Husk removal reduced water status within the maize plant by 22.3–24.5%, thereby decreasing the grain yield due to lower the grain growth rate before grain water content reached the maximum water content level. Grain water status was measured at 3- and 5-day intervals, respectively, in 2019 and 2020 until harvesting, and was incorporated into the path analysis as the independent variable. No irrigation reduced the contribution of the grain growth rate in the early stage to grain dry weight. The grain growth rate in the early grain-filling period was more sensitive to no irrigation than that in the late period. Meanwhile, the differences in grain growth rate between early and late periods promoted grain yield.

Grain abortion is an important factor in reducing the grain number, and mostly occurs at the ear apex [32,33], involving a barren tip of 0.14–2.2 cm, which resulted from husk removal and no irrigation in this study (Figure 5B). Our results revealed that no irrigation and husk removal increased the length of the barren tip and reduced the grain number resulting from water stress at the end of the critical period. This phenomenon is likely to intensify in the context of climate change, where recurrent droughts during flowering and grain initiation phases may amplify grain abortion risks, demanding proactive water-saving interventions. Most of the studies document that the contribution of husk to grain yield mainly lies in the prevention of grain water loss rather than in the production of photo-assimilation [34,35,36,37]. Therefore, husk removal impedes grain growth, in association with grain water content instead of assimilation supply. Further analysis found that the dynamic of grain water content was significantly correlated with grain number and weight (p < 0.05); that is, grain water content as a potential predictor regulated grain abortion and grain filling, especially in the early growth stage or under a water deficit. This physiological mechanism linking water status and yield components reinforces the urgency of developing drought-resilient hybrids with improved husk traits, coupled with irrigation scheduling aligned with the critical period. In this study, the same treatments were maintained across the two experimental years, with different precipitation levels and temperatures, to quantify the yield and water productivity trade-offs under identical management conditions, and to evaluate treatment resilience to uncontrolled climate stress. Water management during the critical period is expected to be more important [7,14,32]. In addition, no irrigation inhibited grain filling and reduced grain weight and yield (Figure 5) [16,17,38]. Regression analysis also showed that grain dry weight increased linearly with the increase in grain water content across the treatments and experimental years (Figure 7). The final grain weight is strongly associated with grain water status in maize, and potential grain weight can be estimated based on the maximum grain water content [8]. These insights provide a physiological basis for designing climate-adaptive management systems that prioritize grain water status as a proxy for both yield potential and water-use efficiency.

5. Conclusions

Grain yield depends strongly on the grain growth rate during the period from silking to the time when grain water content reaches the maximum level, during which grain number and grain weight are closely related to grain water content. In the context of climate change, this critical period is increasingly vulnerable to water scarcity, necessitating strategies that safeguard grain water status while minimizing irrigation demands, a dual imperative that involves navigating the inherent trade-off between maximizing yield and minimizing water use for sustainable intensification. Husk removal at the end of the critical period decreases grain water content by 48.3–54.1%, thus reducing grain number by 7.7–16.9%. The reduced grain water content resulting from husk removal also reduces the final grain weigh by 23.4–24.1%. These findings highlight the critical trade-off required in husk removal, which accelerates grain desiccation and reduces the potential yield under drought, underscoring the need for climate-adaptive husk management to ensure sustainability and high-water productivity. Irrigation mitigated the negative effects of husk removal on grain water content but not on grain yield, reflecting the trade-offs between yield enhancement and grain desiccation in maize production. These trade-offs are particularly salient in water-limited regions, where climate change exacerbates seasonal droughts, urging a paradigm shift toward precision irrigation combined with genotype-specific husk optimization to maximize water productivity. The genotypic differences in husk traits should be considered in irrigation management strategies aimed at coping with water deficit stress in maize production. Future breeding programs targeting climate resilience should prioritize husk architecture, including tightness and length, as a trait to buffer yield losses under erratic rainfall conditions, thereby reducing reliance on supplemental irrigation and enhancing systemic water-use efficiency. This integrated approach, involving irrigation strategies and husk-mediated grain water conservation mechanisms, directly addresses the immediate physiological challenges of grain desiccation and yield stability. Furthermore, it contributes to long-term agricultural sustainability in the context of climate change by effectively balancing grain filling and desiccation across diverse environments.