Meta-Analysis of the Effects of Straw Incorporation on Maize Yield and Water Use Efficiency in China under Different Production Conditions

Abstract

Maize plays a crucial role in China’s grain production, with a cultivation area reaching 44.22 million hectares and an annual yield of 289 million tons in 2023. However, the challenge remains on how to further increase maize yield and water use efficiency (WUE) without adding to the environmental burden. To systematically evaluate the impact of straw incorporation under varying production conditions on maize yield and WUE, this study collected experimental data from multiple locations across China. A meta-analysis was conducted to compare the effects of straw incorporation versus no incorporation, and the main influencing factors were identified using correlation analysis and a random forest model. The results indicate that straw incorporation significantly enhances both maize yield and WUE, with the most pronounced improvements observed under conditions of an average growing season temperature of 19–23 °C, soil pH of 6.5–7.5, low initial soil organic matter content, and deep plowing for straw incorporation. Additionally, moderate nitrogen application rates and straw incorporation amounts (9000–15,000 kg·ha⁻²) also significantly boost maize yield and WUE. Field management practices and meteorological conditions are identified as the primary factors affecting maize yield and WUE under straw incorporation conditions. Therefore, straw incorporation stands out as an effective agricultural practice for achieving high maize yields and efficient resource utilization. The findings of this study provide valuable insights for global food security and the sustainable development of agriculture.

1. Introduction

Maize plays a crucial role in China’s grain production [1]. In 2023, the maize planting area in China reached 44.22 million hectares, accounting for 37.17% of the country’s total grain planting area, with an annual output of 289 million tons, representing 41.54% of the national grain production (National Bureau of Statistics, https://www.stats.gov.cn/). As the global population continues to grow and agricultural production advances, food security and environmental protection have become urgent global issues [2]. Against this backdrop, straw incorporation as a sustainable and environmentally friendly agricultural practice has garnered widespread attention [3]. Straw incorporation can significantly enhance maize yield and water use efficiency (WUE) by increasing soil organic matter content, improving soil structure, and fertility. Additionally, it helps reduce environmental pollution caused by the burning of crop residues, thus promoting green agricultural development [4]. However, due to significant differences in regional meteorological conditions, soil types, and field management practices, the relationship between maize yield and WUE responses to straw incorporation under different conditions remains unclear [5]. Meta-analysis, as a method for integrating and quantifying results from multiple independent studies, offers unique advantages for analyzing experimental data from different regions [6]. Therefore, systematically evaluating the impact of straw incorporation on maize yield and WUE under various production conditions through meta-analysis is not only of significant academic value but also provides scientific evidence for improving agricultural production efficiency and resource utilization.

A considerable number of experiments have been conducted by scholars to investigate the effects of straw incorporation on maize yield and WUE. Appropriate straw incorporation can significantly increase maize yield and WUE [7]. Combining straw incorporation with nitrogen fertilization can significantly improve soil moisture and temperature conditions before sowing, thereby enhancing WUE and maize yield [8]. However, due to variations in climate conditions, soil properties, and straw characteristics, the responses of maize yield and WUE to straw incorporation are inconsistent [9]. For example, Wang et al. studied the effects of different straw incorporation rates combined with a fixed level of inorganic fertilizers on maize growth and WUE in the Loess Plateau of China from 2008 to 2010. The results indicated that a reasonable straw incorporation level, particularly a moderate amount of 9.0 t·hm⁻², significantly improved biomass yield and WUE in semi-arid areas, contributing to agricultural sustainability [10]. Zhang et al. at the Jilin Academy of Agricultural Sciences in China showed that in semi-humid areas, straw incorporation reduced soil moisture evaporation, increased soil water storage, promoted maize photosynthesis and dry matter accumulation, and significantly improved maize yield and WUE [11]. However, some studies have shown that straw incorporation either has no effect or even negative impacts on grain yield or WUE [12]. For instance, Liu et al. conducted a two-year field experiment at the Changwu Agro-ecological Station in China, assessing the effects of different water management measures on spring maize yield and WUE. The results showed that straw incorporation had no significant impact on spring maize yield and WUE [13]. Fan et al. found that maize growth under straw incorporation treatment was poor, with reduced leaf transpiration, decreased WUE, reduced effective leaf area, and consequently negative impacts on photosynthesis and yield [14]. Therefore, to clarify the response patterns of maize yield and WUE to straw incorporation under different production conditions, it is necessary to comprehensively analyze previous experimental results and identify the main driving factors affecting yield and WUE.

Meta-analysis is a statistical method for synthesizing results from similar studies. Initially used in medical research, it has been widely applied in ecological assessments and agricultural research in recent years [15]. For instance, Yu et al. collected 837 observations from 50 published papers and used meta-analysis to investigate the effects of straw and plastic film mulching on maize yield, WUE, and evapotranspiration (ET) under different precipitation and temperature gradients, as well as soil types. The results showed that straw and plastic film mulching significantly increased maize yield and WUE [16]. However, due to significant seasonal variations in meteorological conditions in the study areas, most previous studies have used annual scales (e.g., annual average rainfall and temperature) as influencing factors, which do not accurately reflect the meteorological conditions during the actual crop growing period, greatly affecting the accuracy of research results [17]. Moreover, previous meta-analyses have only analyzed the effects of various factors on crop yield and WUE without identifying the key factors influencing maize yield and WUE under straw incorporation conditions.

Therefore, this study uses meta-analysis with no straw incorporation as a control to quantitatively analyze the effects of straw incorporation on maize yield and WUE under different growing season meteorological conditions, soil conditions, and field management practices. By conducting correlation analysis and relative importance ranking based on the random forest model, we identified the main factors influencing maize yield and WUE under straw incorporation conditions. The study aims to systematically evaluate the effects of straw incorporation on maize yield and WUE under different production conditions, providing a theoretical basis for reasonable straw incorporation in maize cultivation, improving yield and WUE, and reducing resource waste, as well as offering scientific guidance and practical recommendations for agricultural production.

2. Materials and Methods

2.1. Data Collection

This study employs meta-analysis to investigate the effects of straw incorporation on maize yield and water use efficiency under different production conditions. Using keywords such as “maize”, “corn”, “straw incorporation”, “yield”, “water use efficiency” and “China”, we searched for the literature published before December 2023 from databases including China National Knowledge Infrastructure (CNKI), Google Scholar, Web of Science, and Science-Hub. The selection criteria were as follows: (1) The study area is in China, and the experimental procedures are clearly documented, including time, location, and management practices. (2) The experiment includes at least one treatment group with no straw incorporation and one with straw incorporation, with other field conditions being consistent. (3) The study provides data on maize yield, water consumption, or water use efficiency, with sample size and standard deviation available. Based on these criteria, we collected 125 published Chinese and English articles, including 67 Chinese articles and 58 English articles, obtaining 659 sets of yield data and 485 sets of water use efficiency data. The distribution map of the experimental regions from the selected literature is shown in Figure 1.

The data extracted from the literature primarily include information on maize planting locations, meteorological conditions, soil conditions, and field management practices. Since the units used to describe variables in the literature, such as soil organic matter content and straw incorporation amounts, are not consistent, we standardized the units of these variables during data processing. The specific details are provided in

Table 1. Variable descriptions extracted from publications.

Variable	Definition	Data Type/Unit
Title	Title of Each Study	Text
Latitude and longitude	Latitude and longitude of each study site	Text
Rainfall during growth period	The total amount of precipitation received during the entire growth cycle of maize	mm
Average temperature during growing season	The mean temperature recorded throughout the maize growing period	°C
Yearly sunshine hours	The total amount of sunlight received in a year	h
Soil texture	The composition of soil based on the proportions of sand, silt, and clay	Text
Soil pH	A measure of the acidity or alkalinity of the soil	Data
Soil organic matter content	The amount of decomposed plant and animal residues in the soil	g·kg−1
Dry farming/Irrigation	Farming without supplemental irrigation versus farming with the application of water to maize	Text
Planting density	The number of maize plants per unit area	×104·hm−2
Nitrogen application rate	The amount of nitrogen fertilizer applied per unit area	kg·hm−2
Straw types	Different kinds of crop residues	Text
Amount of straw incorporation to field	The quantity of straw residues incorporated back into the soil	kg·hm−2
Forms of Straw Incorporation	The various methods used to incorporate straw into the soil	Text
Yield	The total production of maize per unit area	kg·hm−2
Water Use Efficiency	The ratio of maize yield to the amount of water used	kg/(hm2·mm)

.

Since 85.1% of the collected experimental data were from rainfed conditions and 14.9% were from supplemental irrigation conditions, and the majority of the straw types were from previous crops, with wheat straw accounting for 25.78%, maize straw for 70.11%, and other types of straw for 4.11%, these factors will not be considered in the data classification.

2.2. Data Classification

The collected data were classified and statistically analyzed based on major factors including meteorological conditions (e.g., rainfall during the growing season, average temperature during the growing season, annual sunshine hours), soil conditions (e.g., soil type, pH value, organic matter content by mass), and farmland management practices (e.g., planting density, nitrogen application rate, straw incorporation amount). If the literature did not provide rainfall and average temperature data for the crop growing season, daily rainfall and temperature data for the crop growing season were downloaded from the China Meteorological Data Network (http://data.cma.cn/) to calculate the cumulative rainfall and average temperature for the growing season. In cases where experimental site data were missing, meteorological data from nearby stations with similar geographic location, topography, and average annual rainfall and temperature were used as substitutes. The specific classification of each data type is shown in

Table 2. Data classification.

Natural Factors						Field Management Measures
Weather Condition			Soil Properties			Planting Density/(×104·hm−2)	Nitrogen Application Rate/(kg·hm−2)	Amount of Straw Incorporation to Field/(kg·hm−2)	Forms of Straw Incorporation
Rainfall during Growth Period/mm	Average Temperature during Growing Season/°C	Yearly Sunshine Hours/h	Soil Texture	Soil pH	Soil Organic Matter Content/(g·kg−1)
<400	<19	<2200	Clay	<6.5	<10	<5.25	<120	<6000	Mulch
400–600	19–23	2200–2600	Loam	6.5–7.5	10–20	5.25–6.75	120–240	6000–9000	Rotary tillage
>600	>23	>2600	Sandy	>7.5	>20	>6.75	>240	9000–15,000	Deep cultivation
								>15,000

.

If the study provides WUE data that meets the required standard, we will directly collect that data. If WUE is presented in other units such as kg·m⁻³, it will be converted to “kg/(hm²·mm)”. If WUE data is not provided but yield and water consumption during the growing season are available, we will calculate the WUE using the following formula:

$$WUE={\displaystyle \frac{Y}{ET}}$$

(1)

where Y is the crop’s economic yield (kg·hm⁻²), and ET is the water consumption during the crop’s growing season (mm).

2.3. Data Analysis

2.3.1. Effect Size Calculation

The effect size is a parameter that reflects the impact of experimental treatments, and it can be used to evaluate the consistency of all independent studies by calculating the effect size of each individual study. This allows for the calculation of the overall effect size for the total study, leading to the final meta-analysis results [18]. The effect size (RR) is calculated to quantify the impact of straw incorporation on yield and water use efficiency, using a log-transformed response ratio as follows [19]:

$$RR=\ln \left(x_e/x_c\right)=\ln \left(x_e\right)-\ln \left(x_c\right)$$

(2)

where $RR$ is the effect size, $x_e$ is the yield or water use efficiency under straw incorporation, and $x_c$ is the yield or water use efficiency without straw incorporation.

To express the effect of straw incorporation on yield or water use efficiency more intuitively, the effect size was converted into a percentage (%) as follows:

$$I=\left(e^{RR}-1\right)\times 100\mathrm{\%}$$

(3)

The variance (ν) for a single effect size was calculated using:

$$\nu \left(RR\right)={\displaystyle \frac{S_{\mathrm{e}}^2}{n_e{x}_e^2}}+{\displaystyle \frac{S_c^2}{n_c{x}_c^2}}$$

(4)

where $S_e$ and $S_c$ are the standard deviations of yield or water use efficiency under straw incorporation and no straw incorporation, respectively; $n_e$ and $n_e$ are the sample sizes of the treatment group and control group, respectively.

The weight (W) for comparisons in the meta-analysis was calculated as follows [20]:

$$W_i={\displaystyle \frac{1}{V_i}}$$

(5)

where $W_i$ is the weight factor for study i, adjusted for the total number of observations at each site when multiple observations are extracted from a single study [21]. Studies with smaller within-study variance are given greater weight, indicating the importance of that indicator in the overall evaluation.

The weighted response ratio ($R{R}_{++}$) for the overall effect of straw incorporation compared to no straw incorporation on yield and water use efficiency was calculated as:

$$R{R}_{++}={\displaystyle \frac{\sum _{i=1}^m\sum _{j=1}^k{w}_{ij}R{R}_{ij}}{\sum _{i=1}^m\sum _{j=1}^k{w}_{ij}}}$$

(6)

where $R{R}_{++}$ is the weighted response ratio for treatment groups (straw incorporation) and control groups (no straw incorporation), m is the number of groups being compared, and k is the number of comparisons within the corresponding group.

The standard error of $R{R}_{++}$ was calculated as:

$$s\left(R{R}_{++}\right)=\sqrt{{\displaystyle \frac{1}{\sum _{i=1}^m\sum _{j=1}^k{w}_{ij}}}}$$

(7)

The 95% confidence interval (95% CI) was calculated as follows:

$$95\mathrm{\%}CI=R{R}_{++}\pm 1.96\times s\left(R{R}_{++}\right)$$

(8)

For studies where the standard deviation (SD) was not provided but the standard error (SE) was given, the SD was calculated using the following formula:

$$SD=SE\cdot \sqrt{n}$$

(9)

If both SD and SE were not provided, the missing SD values were estimated using the coefficient of variation (CV) [22]. First, the CV for a single study was calculated using the given mean (m) and SD: $CV=SD/\mathfrak{m}$. Next, the average CV ($\overline{CV}$) across all data was computed. Finally, the missing SD values were estimated as:

$$SD=\mathrm{m}\cdot \overline{CV}$$

(10)

MetaWin 2.1 software was used to calculate effect sizes and 95% confidence intervals (95% CI). The required input data included the mean values, standard deviations, and sample sizes of yield and water use efficiency under straw incorporation and no straw incorporation. If the 95% CI was entirely above zero, it indicated that straw incorporation significantly increased yield or water use efficiency; if the 95% CI included zero, it indicated no significant effect; and if the 95% CI was entirely below zero, it indicated that straw incorporation significantly decreased yield or water use efficiency.

2.3.2. Heterogeneity and Bias Testing

Heterogeneity in the data was tested using the I² statistic:

$$\mathrm{Q}=\sum _{\mathrm{i}=1}^{\mathrm{n}} {\mathrm{w}}_{\mathrm{i}}({\mathrm{E}}_{\mathrm{s}\mathrm{i}}^2-{\mathrm{E}}_{\mathrm{s}}{)}^2$$

(11)

$${\mathrm{I}}^2=[\mathrm{Q}-(\mathrm{n}-1\left)\right]/\mathrm{Q}$$

(12)

where ${\mathrm{w}}_{\mathrm{i}}$ is the weight of the i-th data set, n is the number of effect sizes, ${\mathrm{E}}_{\mathrm{s}\mathrm{i}}$ is the effect size of the i-th study, and ${\mathrm{E}}_{\mathrm{s}}$ is the mean effect size of all studies. If I² ≥ 50%, it indicates heterogeneity in the data, and a random-effects model is used for analysis; otherwise, a fixed-effects model is used.

Publication bias was tested using a violin plot of the distribution of effect sizes (RR) and Rosenthal’s Fail-safe test [23]. If N > 5n + 10 (where N is the fail-safe number and n is the sample size) and the violin plot shows good symmetry, the study is considered free from publication bias.

2.4. Data Processing

Using MetaWin 2.1 software, the meta-analysis was conducted by calculating effect sizes and their variances, applying fixed-effect or random-effect models (such as the DerSimonian-Laird method) for weighted averaging, and assessing data heterogeneity and bias using Q statistics and I² statistics. This approach yields the combined effect size and the 95% confidence interval (95% CI) [24]. Data collection and classification were conducted using Excel 2021. Experimental sites were mapped using ArcGIS 10.8. Figures were created with Origin 2021. Correlation analyses were performed with SPSS 22.0. Feature importance was ranked using machine learning in R 4.1.2, with the “PARTY” package employed to build a random forest model. The frequency distribution of lnR was calculated using Matlab 2019b, and violin plots were generated with the “violinplot” function.

3. Results

3.1. Comprehensive Effect Size Calculation and Tests for Heterogeneity and Bias

The comprehensive effect size, heterogeneity, and bias test results of the selected data are shown in

Table 3. Comprehensive effect size calculation for the impact of straw incorporation on maize yield and water use efficiency.

Indicator	Model	Rate of Increase/%	Confidence Interval/%		Q	I2/%	n	N
			Lower Limit	Upper Limit
Yield	Random effects model	7.19	6.90	7.48	6184.47	91.02	659	27,881.09
Water Use Efficiency	Random effects model	6.16	5.93	6.39	5629.75	90.56	485	60,265.08

. According to the calculation results, I² ≥ 50%, indicating that the heterogeneity test reached a significant level. Therefore, the random effects model was used for the meta-analysis. Compared to no straw incorporation, straw incorporation increased maize water consumption and water use efficiency by 7.19 ± 0.29% and 6.16 ± 0.23%, respectively. The frequency distribution of lnR followed a Gaussian normal distribution (Figure 2), and Rosenthal’s Fail-safe test showed that the fail-safe number N > 5n + 10, indicating no publication bias in this study. Thus, the conclusions are reliable.

3.2. The Impact of Climate Conditions on Maize Yield and Water Use Efficiency under Straw Incorporation

Through the analysis of the collected data, this study found that the impact of straw incorporation on maize yield and water use efficiency is closely related to the climatic conditions of the experimental area. Climatic conditions significantly affect the enhancement effect of straw incorporation on maize yield and water use efficiency.

With the increase in cumulative rainfall during the growing season, the impact of straw incorporation on maize yield initially decreases and then increases (Figure 3a), while the impact on water use efficiency initially increases and then decreases (Figure 3b). In areas with growing season rainfall < 400 mm, straw incorporation significantly increases maize yield but does not markedly improve water use efficiency. When the growing season rainfall is between 400–600 mm, straw incorporation increases maize yield and significantly improves water use efficiency, with increases of 7.18% and 8.19%, respectively. In regions with rainfall > 600 mm, the effects of straw incorporation on yield and water use efficiency are not as pronounced compared to other areas.

Straw incorporation has a regulatory effect on soil temperature, reducing the adverse effects of drastic temperature changes on crops [25,26]. As the average temperature during the growing season increases, the impact of straw incorporation on maize yield and water use efficiency initially increases and then decreases. Compared to regions with a growing season average temperature <19 °C and >23 °C, straw incorporation significantly improves maize yield and water use efficiency when the average temperature during the growing season is between 19–23 °C, with increases of 9.56% (95% CI = 8.94–10.18%) and 7.95% (95% CI = 7.57–8.34%), respectively. The enhancement effect of straw incorporation on maize yield and water use efficiency increases initially and then decreases with the increase in annual sunshine hours. In regions with annual sunshine hours between 2200–2600, straw incorporation significantly promotes yield and water use efficiency, with increases of 8.16 ± 0.49% and 6.78 ± 0.33%, respectively.

3.3. The Impact of Soil Factors on Maize Yield and Water Use Efficiency under Straw Incorporation

The initial properties of the soil (soil texture, soil pH, and soil organic matter content) significantly affect the impact of straw incorporation on maize yield and water use efficiency (Figure 4).

Straw incorporation can enhance the soil’s water-holding capacity and nutrient retention, significantly improving maize yield and water use efficiency. In sandy soils with poor texture and clay soils with good water-holding capacity, straw incorporation can significantly increase maize yield (by 8.02% and 8.08%, respectively) and water use efficiency (by 7.03% and 6.22%, respectively). Compared to sandy and clay soils, the improvement in maize yield and water use efficiency in loamy soils due to straw incorporation is relatively lower, at only 5.88% and 6.16%, respectively. When soil pH is between 6.5–7.5 (neutral soil), the enhancement of maize yield and water use efficiency by straw incorporation is stronger than in soils with pH < 6.5 (acidic soil) and pH > 7.5 (alkaline soil), with increases of 10.41% (95% CI = 9.20–11.62%) and 7.32% (95% CI = 6.36–8.27%), respectively. Soil organic matter content is negatively correlated with the improvement in maize yield and water use efficiency due to straw incorporation. In soils with low initial organic matter content, the promotion effect of straw incorporation on maize yield and water use efficiency is most significant, with increases of 9.72% and 10.52%.

3.4. The Impact of Key Field Management Practices on Maize Yield and Water Use Efficiency under Straw Incorporation

The effect of straw incorporation on maize yield diminishes with increasing planting density (Figure 5a), while its impact on water use efficiency initially decreases and then increases (Figure 5b). When the planting density is less than 52,500 plants hm⁻² (low density), the influence of straw incorporation on maize yield and water use efficiency is most significant, with increases of 10.35 ± 0.79% and 9.20 ± 0.47%, respectively.

Straw incorporation effectively supplements soil organic matter, thereby improving soil fertility and providing more nutrients to meet the rapid growth demands of crops. When the nitrogen application rate in the field is less than 120 kg·hm⁻², straw incorporation significantly enhances maize yield and water use efficiency, with increases of up to 13.17% (95% CI = 12.14–14.20%) and 13.00% (95% CI = 12.31–13.69%), respectively. However, when the nitrogen application rate exceeds 120 kg·hm⁻², the improvement effects on yield and water use efficiency are relatively small.

The impact of straw incorporation on maize yield and water use efficiency shows an initial increase followed by a decrease as the amount of straw incorporated increases. An optimal amount of straw incorporation can maximize improvements in soil organic matter, structure, and fertility, thereby enhancing yield and water use efficiency. Conversely, too little or too much straw incorporation may limit or even reduce its positive effects. When the amount of straw incorporated is between 9000 and 15,000 kg·hm⁻², the increases in maize yield and water use efficiency reach their maximum values, at 11.50% and 11.98%, respectively. When the amount of straw incorporated is too low or too high, the impact on yield and water use efficiency is not significant. Additionally, compared to straw mulching and rotary tillage incorporation, deep plowing of straw into the soil has been shown to significantly enhance maize yield and water use efficiency, with increases of up to 9.07% and 9.34%, respectively.

3.5. Correlation Analysis and Relative Importance Ranking of the Impact of Straw Incorporation on Maize Yield and Water Use Efficiency

The results of the linear regression analysis (Figure 6) indicate that the effect of straw incorporation on maize yield is significantly positively correlated with nitrogen application rate (R² = 0.15, p < 0.05), soil texture (R² = 0.13, p < 0.05), and annual average sunshine hours (R² = 0.10, p < 0.01). Conversely, it is significantly negatively correlated with soil pH (R² = 0.11, p < 0.01). For maize water use efficiency, straw incorporation is significantly positively correlated with nitrogen application rate (R² = 0.23, p < 0.001) and average temperature during the growth period (R² = 0.14, p < 0.005), and significantly negatively correlated with soil pH (R² = 0.37, p < 0.001) and annual average sunshine hours (R² = 0.16, p < 0.001).

Random forest regression models are commonly used to explore the relative importance of meteorological conditions, soil properties, and agricultural management practices in agriculture [27]. The results showed that the factor with the greatest influence on maize yield variation due to straw incorporation was planting density (24.76%), followed by average temperature during the growing season (19.49%), amount of straw incorporation (15.55%), nitrogen application rate (14.20%), and rainfall during the growing season (12.26%) (Figure 7a). For water use efficiency, the most significant factor was soil pH (24.19%), followed by meteorological conditions (36.36%) and planting density (17.21%) (Figure 7b).

4. Discussion

4.1. Overall Impact of Returning Straw to Fields on Maize Yield and Water Use Efficiency

The meta-analysis results showed that, compared with no straw incorporation, straw incorporation significantly increased maize yield and water use efficiency by 7.19 ± 0.29% and 6.16 ± 0.23%, respectively. This yield increase due to straw incorporation differs slightly from previous studies by Islam (12.5%) [28] and Qin X (9.96% and 14.04%) [29]. These differences may be due to the larger sample size in our study, which provides a more comprehensive estimate of the impact of straw incorporation on maize yield and water use efficiency in China. Additionally, these differences may be related to significant variations in climate conditions, initial soil conditions, and field management practices [30].

The analysis of relative importance showed that 56.01% of the variability in maize yield response to straw incorporation can be explained by field management practices, 34.81% by meteorological conditions, and 9.18% by initial soil conditions (Figure 7a). For water use efficiency, 36.36% of the variability can be explained by meteorological conditions, 34.45% by initial soil conditions, and 29.19% by field management practices (Figure 7b). This indicates that these variables have a profound impact on crop yield and water use efficiency, and a thorough understanding of these variables is essential when considering effective strategies for optimal maize yield and water use efficiency.

4.2. Impact of Climatic Conditions on Maize Yield and Water Use Efficiency with Straw Incorporation

Climate is one of the key factors influencing crop growth, development, yield, and water use efficiency [31]. Straw incorporation affects maize yield and water consumption by altering the soil’s physical and chemical properties [32], and climatic factors are the main drivers of straw decomposition. Therefore, climatic factors indirectly impact maize yield and water use efficiency. This study indicates that climatic conditions largely determine the effectiveness of straw incorporation in enhancing maize yield and water use efficiency [33].

Straw incorporation under different climatic conditions shows significant variations in its effect on maize yield and water use efficiency (Figure 6). Soil moisture retention is crucial for crop growth. Straw incorporation reduces soil surface evaporation and increases soil moisture storage, thereby ensuring adequate water supply for crops under limited water conditions and significantly enhancing maize yield [34]. Our study demonstrates that in regions with cumulative rainfall during the growing period ranging from 400–600 mm, straw incorporation not only provides sufficient water supply but also avoids nutrient loss and water excess due to excessive rainfall, enabling efficient utilization of water and nutrients and achieving optimal water use efficiency. Insufficient nutrient supply in the soil directly affects crop growth and yield [35]. Straw incorporation affects the temperature of the crop’s soil environment, thereby influencing the straw decomposition process and soil microbial activity, which in turn affects soil organic matter and nutrient levels [36]. Our study finds that the optimal straw incorporation effect occurs when the average temperature during the growing period is between 19–23 °C. This is because suitable temperatures promote microbial activity and straw decomposition while avoiding the adverse effects of extreme temperatures on soil moisture and crop growth. Under these conditions, soil organic matter and nutrients are effectively released and utilized, and soil water retention is maintained, thereby significantly improving maize yield and water use efficiency. Furthermore, sunlight affects soil microbial activity, and straw incorporation provides abundant organic matter, promoting microbial activity. Active microbial communities can accelerate straw decomposition, releasing nutrients and further enhancing soil fertility [37]. Adequate sunlight hours provide sufficient photosynthesis to promote crop growth while avoiding excessive water evaporation and photothermal stress caused by too much sunlight [38]. Under these conditions, soil moisture is retained, straw decomposition is moderate, and nutrient release and absorption efficiency are high, significantly improving maize yield and water use efficiency.

Moreover, the results of the relative importance of variables indicate that climatic conditions have a significant impact on crop yield and water use efficiency during straw incorporation (Figure 7). Therefore, providing adequate soil moisture, temperature, and sunlight during straw incorporation is crucial for enhancing crop yield and water use efficiency [39].

4.3. Impact of Soil Conditions on Maize Yield and Water Use Efficiency with Straw Incorporation

The response of maize yield and water use efficiency to straw incorporation is also influenced by the initial physical and chemical properties of the soil, including soil texture, soil pH, and initial soil organic matter content [40]. The enhancement effect of straw incorporation on yield and water use efficiency is more significant in soils with poor initial conditions, while in soils with better conditions, its role is more in maintaining and optimizing the existing soil health levels. By improving soil organic matter, structure, and water retention capacity, straw incorporation can significantly or moderately increase crop yield and water use efficiency under different initial conditions.

Straw incorporation has significantly different effects on maize yield and water use efficiency under different soil types [41]. Our study shows that in loam soils, although straw incorporation is still beneficial, its effect is not as pronounced as in clay and sandy soils. Despite loam soils having good water and nutrient retention capabilities, their structure is already relatively ideal, so the improvement effect of straw incorporation is not as significant as in clay and sandy soils. Loam soils already provide a relatively suitable growth environment, and the further improvement space for straw incorporation is limited. Therefore, under loam soil conditions, the enhancement effect of straw incorporation on maize yield and water use efficiency is the least. Additionally, the regulation effect of straw incorporation on soil pH can effectively improve the soil environment, enhancing nutrient availability and microbial activity, thereby increasing maize yield and water use efficiency [42]. Our analysis results show that under neutral soil conditions, with soil pH close to 7, it is suitable for the growth and activity of most microbes, leading to a fast straw decomposition rate and sufficient organic matter and nutrient release. Neutral soils have good nutrient supply capabilities and structure, allowing crops to fully absorb and utilize nutrients, promoting growth and development, thereby significantly enhancing maize yield. Meanwhile, the structure and texture of neutral soils are most suitable for water retention and conduction, optimizing water use efficiency. Therefore, straw incorporation shows the best effect under neutral soil conditions. Additionally, straw incorporation can significantly increase soil organic matter content, improve soil structure and fertility, helping to enhance crop yield and water use efficiency [43]. In soils with initial organic matter content < 10 g·kg⁻¹, the soil structure is poor, and the water and nutrient retention capacity is limited. Straw incorporation significantly improves the soil’s physical and chemical properties by increasing soil organic matter, enhancing soil water retention and nutrient supply. This significant improvement effect is particularly prominent in soils with low initial organic matter content, thereby greatly enhancing maize yield and water use efficiency.

4.4. Impact of Field Management Practices on Maize Yield and Water Use Efficiency with Straw Incorporation

The response of maize yield and water use efficiency to straw incorporation largely depends on the effective coordination of field management practices. Reasonable planting density, scientific nitrogen application levels, and appropriate straw incorporation amounts can maximize the positive effects of straw incorporation, thereby achieving high maize yield and high efficiency [44]. Straw incorporation management and field tillage practices can change the movement of water in the soil and the dynamic changes of carbon and nitrogen, causing differences in soil productivity, thus affecting the changes in crop yield and water use efficiency [45]. Our study found that planting density has an important impact on the effect of straw incorporation. When maize planting density is less than 52,500 plants·hm⁻², there is less competition between maize plants, and each maize plant can obtain more resources, such as light, water, and nutrients. Under such conditions, straw incorporation further increases soil organic matter content, improves soil structure, and enhances water and nutrient supply capacity. As each maize plant receives sufficient resources, it grows more vigorously, thereby significantly increasing overall yield and water use efficiency. As planting density increases, competition between maize plants intensifies, and resource distribution becomes more even [46]. Although straw incorporation can also increase soil organic matter content and improve soil structure, the competition pressure between plants limits the resources each maize plant can receive, leading to less significant yield improvement effects. Meanwhile, due to high competition pressure, the enhancement of water use efficiency is also limited, showing relatively poorer results. Appropriate nitrogen application during straw incorporation can stimulate soil microbial activity, increase straw decomposition, and be more conducive to crop growth, thereby improving crop yield and water use efficiency [47]. Our study found that when field nitrogen application is less than 120 kg·hm⁻², soil nitrogen supply is relatively insufficient, and straw incorporation significantly enhances soil’s nutrient retention and supply efficiency by increasing soil organic matter content and improving soil structure. Under such conditions, slow decomposition of straw releases nitrogen gradually, meeting the nitrogen needs for crop growth, thus effectively increasing maize yield. Additionally, soil organic matter can better retain water, improving water use efficiency, allowing crops to achieve high productivity even under relatively low nitrogen supply [48].

The impact of straw incorporation on maize yield and water use efficiency shows an “optimal amount” relationship with the amount of straw incorporated. When the straw amount is too little, it cannot significantly improve soil organic matter content and structure, and the enhancement of soil water retention and nutrient supply capacity is limited, thus the effect on maize yield and water use efficiency is the poorest [49]. Under such conditions, the soil improvement effect of straw incorporation is insufficient, failing to fully exert its potential yield and water-saving effects. When the straw incorporation amount is 9000–15,000 kg·hm⁻², soil organic matter content significantly increases, improving soil physical and chemical properties. An appropriate amount of straw incorporation can effectively enhance soil water retention and nutrient supply, promote soil microbial activity, and enhance soil fertility, thus providing a good environment for maize growth [50]. Within this range of straw incorporation, the decomposition rate of straw is moderate, continuously releasing nutrients to meet the needs of maize at different growth stages, ultimately significantly enhancing yield and water use efficiency. When the straw amount is too high, although soil organic matter content further increases, excessive straw may deteriorate soil aeration, affecting root respiration and growth. Moreover, an excess of organic matter may temporarily immobilize nitrogen in the soil, causing nitrogen starvation, limiting maize nitrogen absorption and utilization [51]. Therefore, despite significant soil improvement, these negative impacts result in less significant yield and water use efficiency enhancement. In the context of deep plowing for straw incorporation, the enhancement effects on maize yield and water use efficiency are most significant. Compared to other methods, deep plowing effectively buries the straw deeper in the soil, which increases soil moisture retention capacity and significantly improves soil structure and nutrient availability [52]. This approach facilitates the decomposition of straw and the release of organic matter, providing a steady nutrient supply for the crops while also reducing the extreme fluctuations in soil temperature, thereby creating a more favorable environment for crop growth. Furthermore, deep plowing reduces the risk of nutrient loss from the soil surface, contributing to further improvements in water use efficiency [53]. However, considering that deep plowing can lead to higher production costs, it is necessary to balance economic considerations with the goal of maximizing the benefits of straw incorporation.

Thus, optimal planting density, nitrogen application rates, the amount of straw incorporation, and the method of straw incorporation are critical for effective straw management. These factors should be carefully evaluated in practical agricultural practices to achieve the best outcomes.

5. Conclusions

Straw incorporation significantly enhances maize yield and water use efficiency. In regions with a growing season precipitation of 400–600 mm, the benefits of straw incorporation are more pronounced. The improvement effect of straw incorporation is also more significant in soils with low organic matter content. Appropriate nitrogen application rates and straw incorporation quantities have a greater positive impact on maize yield and water use efficiency. The main factor influencing changes in maize yield due to straw incorporation is field management practices (56.01%), while the primary factor influencing water use efficiency is meteorological factors (36.36%). Straw incorporation has the potential to increase crop yield and water use efficiency. Our study indicates that, under different climate and soil conditions, when combined with appropriate planting density, nitrogen application, and other management practices, straw incorporation can be a sustainable agricultural practice with significant potential for widespread adoption.

This research can provide theoretical guidance for developing highly adaptable and practical straw incorporation techniques tailored to different corn-growing regions in China, thereby promoting their application and dissemination in actual agricultural production.