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Article

Concurrent Response of Greenhouse Soil NO3− Concentration and N2O Emissions to Nitrogen and Irrigation Management in China: A Meta-Analysis

by
Guiliang Wang
1,
Haojie Xu
1,
Kaiyuan Huang
1,
Jinchuang Wang
2,
Haitao Zhao
1,
Xiaoqing Qian
1 and
Juanjuan Wang
1,*
1
College of Environmental Science and Engineering/Key Laboratory of Cultivated Land Quality Monitoring and Evaluation, Ministry of Agriculture and Rural Affairs/Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, Yangzhou University, Yangzhou 225127, China
2
Environmental and Plant Protection Institute, Chinese Academy of Tropical Agricultural Sciences, Haikou 570100, China
*
Author to whom correspondence should be addressed.
Agronomy 2024, 14(7), 1387; https://doi.org/10.3390/agronomy14071387
Submission received: 7 June 2024 / Revised: 22 June 2024 / Accepted: 25 June 2024 / Published: 27 June 2024
(This article belongs to the Special Issue Applied Research and Extension in Agronomic Soil Fertility Series II)
Browse Figures
Versions Notes

Abstract

The soil NO3− concentration and N2O emissions plays a crucial role in mitigating greenhouse gas emissions and minimizing greenhouse soil degradation concurrently. However, it is essential to understand the extent to which management practices and environmental factors influence the reduction in NO3− concentration and N2O emissions in greenhouse soils. Here, we conducted a meta-analysis, compiling a database of NO3− concentration and N2O emissions in response to either nitrogen or irrigation management in greenhouse vegetable-based systems in China. In summary, controlling the amount of total nitrogen application and irrigation water within specific ranges can effectively reduce both the greenhouse NO3− concentration and N2O emissions. Compared to chemical nitrogen management, the application of slow-release fertilizer could concurrently reduce the soil NO3− concentration and N2O emissions by 0.20 and 0.36 times, respectively. Positive relationships were observed between soil NO3− concentration and N2O emissions under conditions of higher soil organic carbon (OC), total nitrogen (TN), alkali-hydrolyzed nitrogen (AN), and pH, as well as a lower soil temperature (ST) and bulk weight (BW). Under conditions with a higher OC and pH, an appropriate nitrogen application rate is more effective in reducing N2O emissions. While increasing irrigation can reduce soil NO3− concentrations, it also raises the risk of significant NO3− leaching. Overall, nitrogen and irrigation management should be tailored to local soil physicochemical properties to concurrently regulate soil NO3− concentrations and N2O emissions in greenhouse environments.

1. Introduction

In China, about 30 percent of vegetables are produced in greenhouses, which is about 85% of the global greenhouse vegetable production area [1,2]. In order to achieve high production, farmers traditionally apply large amounts of nitrogen fertilizer along with substantial irrigation. In these greenhouses, both nitrogen and water input greatly exceed the crops’ demand for them [3,4]. This excess nitrogen, which cannot be absorbed by crops, either remains in the soil profile, where it could lead to soil nutrient imbalances, salinization, and degradation [5], or is lost to the atmosphere in the form of the greenhouse gas nitrous oxide (N2O) [6,7,8]. In China, the mean soil N2O emissions from greenhouse vegetable cropping systems are approximately 12.4 kg N2O-N hm−2 yr−1, significantly higher than emissions from open-field systems [2]. Therefore, understanding the influencing factors and driving effects of soil nitrogen concentration and N2O emissions in the greenhouse is of great importance for developing effective management measures to mitigate greenhouse gas emissions and minimize greenhouse soil degradation.
A large number of studies have shown that nitrogen and irrigation application can significantly affect soil nitrate-N (NO3−) concentration [9,10,11,12,13]. Under the same irrigation conditions, the soil NO3− concentration gradually increased with the rise in the nitrogen application rate. Soil moisture acts as a carrier for nitrogen transport, making the irrigation rate a crucial factor in the distribution of NO3− within the soil profile [9]. Under the same nitrogen application rate, increasing the irrigation rate would promote NO3− leaching downward [10,11]. In conventional production, improper water and nitrogen management often increases the risk of NO3− leaching into deeper soil layers, thereby contributing to nitrogen loss and groundwater pollution [12,13]. Soil N2O emissions constitute a significant pathway for nitrogen loss and contribute to greenhouse gas effects [14]. Numerous relevant studies suggest that both irrigation and nitrogen play crucial roles in influencing N2O emissions in greenhouse soils [15,16]. On one hand, substantial nitrogen application provides abundant N sources, promoting N2O emissions. On the other hand, irrigation practices impact soil moisture levels, alter soil aeration and reoxidation conditions, and consequently affect the processes of nitrification and denitrification, leading to subsequent soil N2O production and release [17]. Those studies about the nitrogen balance of farmland systems, with the regulation of irrigation and nitrogen management can reduce nitrogen leaching and N2O emissions, which provides an important scientific basis for decreasing nitrogen loss, and promoting the efficient use of nitrogen fertilizer and environmentally friendly collaborative development [18,19]. However, there have been few studies examining how nitrogen and irrigation management can concurrently improve greenhouse soil quality and reduce greenhouse gas emissions by lowering NO3− concentrations and N2O emissions.
In addition to irrigation and nitrogen management, the greenhouse soil NO3− concentration and N2O emissions are also influenced by soil environmental factors [19]. A relevant study showed that soil temperature has a significant impact on N2O emissions in farmland. Under the same water and nitrogen application rates, higher temperatures result in higher N2O emissions [20]. Soil moisture conditions not only affect the generation of N2O in soil but also influence its diffusion into the atmosphere. Soil moisture levels affect soil aeration and redox conditions, influencing nitrification and denitrification processes by affecting the distribution of ammonium nitrogen and nitrate nitrogen and their effectiveness on microorganisms. Consequently, this affects soil N2O emissions [21,22]. Additionally, soil physicochemical properties such as soil pH, organic carbon concentration, and nitrogen concentration affect both the nitrification and denitrification processes in soil, exerting varying degrees of influence on soil N2O emissions [23,24]. However, most of these studies were based on field experiments with specific soil properties, which poses a challenge to understanding changes in greenhouse soil N2O emissions and the NO3− concentration under varied soil physicochemical conditions.
This research sought to address three questions regarding the controls on N2O emissions and NO3− concentration in greenhouse soil: first, how do N2O emissions and the NO3− concentration concurrently vary with nitrogen and irrigation management? Second, how do N2O emissions and NO3− concentration co-vary with the variation in soil physicochemical properties? Finally, how do N2O emissions and NO3− concentration respond to nitrogen and irrigation management under different soil physicochemical properties? To address these questions, we compiled a database of N2O emissions and NO3− concentration responses to either nitrogen or irrigation management field studies from greenhouse vegetable-based systems in China. We evaluated the concurrent effects of greenhouse soil NO3− concentration and N2O emissions to nitrogen, irrigation management, and soil environmental factors in China using meta-analysis.

2. Materials and Methods

2.1. Data Compilation

Data were acquired through an exhaustive literature survey of peer-reviewed publications using the China Knowledge Resource Integrated database (CNKI), ISI-Web of Science (Thomson Reuters, New York, NY, USA), and Google Scholar (Google Inc., Mountain View, CA, USA). The literature survey focused on greenhouse vegetable-based field measurements of the NO3− concentration and N2O emissions in the major Chinese greenhouse vegetable-production regions. The keywords used for the search were “irrigation”, “water”, “nitrogen”, or “N fertilization”, in combination with “nitrate” and “N2O”. The resulting literature from this search was further screened to meet the following criteria: (a) the experiment should be conducted on a greenhouse vegetable-based field instead of an open-land vegetable field; (b) only field experiments rather than laboratory incubations or pot studies were included; (c) the duration of the experiment should not be less than one full vegetable growing season; (d) both the soil NO3− concentration at harvest stage and N2O emissions during the whole growth period must be measured concurrently; (e) at least one treatment must be included, including nitrogen fertilizer or irrigation management treatment. When data were graphically presented, the GetData Graph Digitizer (version 2.20) was used to obtain numeric data.
With a priori expectations that many different management and soil factors affect the soil NO3− concentration and N2O emissions, we also compiled numerous other observation-level details, filling in some information from publicly available soil databases. Thus, most observations include data on the fertilizer type (organic fertilizer, straw fertilizer, slow-release fertilizer) and biochar. Nitrification inhibitors added to different N sources were included both as individual products and as broad categories. We connected soil characteristics for each location with all relevant observations. These data included the basic surface soil pH, bulk density, alkali-hydrolyzed nitrogen, total nitrogen, and soil organic carbon (most often 0–20 cm), as well as the average soil temperature and water-filled pore space during the greenhouse vegetable growth period. In addition, the name, latitude, and longitude of each experiment were collected directly.

2.2. Data Description

The final dataset consisted of 427 sets of observations from 49 papers published from 2004 to 2021, including 35 papers that studied both nitrogen fertilizer and irrigation management, and 14 papers that only studied nitrogen fertilizer management (Table S1). The data cover much of North and East China, which are the primary areas for greenhouse vegetable production in China (Figure 1). Studies are lacking in several regions, such as Southwest and South China, regarding either NO3− concentrations, N2O emissions, or both.

2.3. Data Analysis

To quantify the relative percentage changes in nitrogen and irrigation management on the NO3− concentration and N2O emissions from greenhouse vegetable production, we used the natural log-transformed response ratio (R) to estimate the “effect size,” as an index to weigh the response of nitrogen and irrigation variables to the NO3− concentration and N2O emission [25]. First, the natural log response ratio (ln R) was calculated as Equation (1):
ln R = ln (Xt/Xc)
where Xt and Xc are the NO3− concentration (N2O emissions) of the selected dependent variables under nitrogen (irrigation) treatment and in the control, respectively. In the database, experiments with different nitrogen application rates used no nitrogen fertilizer as the control. For experiments with various types of fertilizer treatments, chemical nitrogen management alone served as the control. In experiments involving different irrigation quantities, the conventional irrigation rate was used as the control.
Then, the mean effect size of all observations was calculated according to Equations (2) and (3):
R = exp [Σ ln R(i) × W(i)/Σ W(i)]
EF = R − 1
where W(i) is the weight for the observation for the ith study. EF is the weighted effect size expressed as a relative multiple of change. A positive or negative multiple value indicates an increase or decrease, respectively.
For the meta-analysis, the variables of each study were categorized into the following six functional groups: basic soil physicochemical properties including bulk weight (low, ≤1.3 g cm−1 and high, >1.3 g cm−1), pH (low, ≤7.4 and high, >7.4), organic carbon (low, ≤14 g kg−1 and high, >14 g kg−1), total nitrogen (low, ≤1.7 g kg−1 and high, >1.7 g kg−1), alkali-hydrolyzed nitrogen (low, ≤144 mg kg−1 and high, >144 g kg−1), and the growing period average soil temperature (low, ≤20.4 °C and high, >20.4 °C) and water-filled pore space (WFPS) (low, ≤56.3% and high, >56.3%).
To clarify the potential mechanisms of the heterogeneity of the soil NO3− concentration and N2O emissions in response to nitrogen and irrigation management and soil environmental factors, we used linear or nonlinear regression to analyze the relationships between NO3− concentration or N2O emissions and the nitrogen input and irrigation rate under different soil physicochemical properties conditions. The adjusted r2 was used to determine if the models were the best-fit regression, and the models with higher r2 values were selected. The regression analysis and spearman correlation were conducted with the SPSS software (SPSS 19.0 for Windows, SPSS Inc., Chicago, IL, USA), and the graphs were performed using R (4.3.2). In order to explore the potential direct and indirect effects of nitrogen and irrigation management and soil physicochemical properties on the soil NO3− concentration and N2O emissions, structural equation modeling (SEM) analysis was used by AMOS 24.0 (Amos, Development Corporation, Meadville, PA, USA), and the goodness of model fit was assessed by CHI/DF, AGFI, CFI, and RMSEA.

3. Results

3.1. Data Exploratory Analysis

Histogram and summary descriptive statistics of the measured soil NO3− and N2O values and the total N input and irrigation rate in greenhouse vegetables are shown in Figure 2. The NO3− concentration ranged from 1.2 to 871.7 mg kg−1 (mean = 123.0 mg kg−1) and revealed a positively skewed unimodal distribution (Figure 2A). The N2O emissions ranged from 0.02 to 19.7 kg hm−2 (mean = 2.8 kg km−2) and revealed a positively skewed bimodal distribution with the two modes observed around 0.4 and 2.5 kg hm−2 (Figure 2B). The total N input ranged from 0 to 1600 kg hm−2 (mean = 423.6 kg km−2) and revealed a positively skewed bimodal distribution with the two modes observed around 5.0 and 258.6 kg hm−2 (Figure 2C). The irrigation rate ranged from 21.3 to 747.0 mm (mean value, 209.1 mm) and revealed a positively skewed unimodal distribution (Figure 2D).

3.2. Effects of Nitrogen and Water Management on Soil NO3− Concentration and N2O Emissions

In this study, we found that the soil NO3− concentration was linearly correlated with the total N input (Figure 3A), increased slightly, and then decreased with the irrigation rate (Figure 3C). N2O emissions were exponentially correlated with the total N input (Figure 3B), while no significant relationship with the irrigation rate was observed (Figure 3D).
As can be seen from the heat map analysis (Figure 4), the color of the soil NO3− concentration on the lower right-hand side tended to turn yellow and red, indicating that there is a risk of high NO3− concentration when the total N input is higher and the irrigation rate is lower (Figure 4a). The color of N2O emissions on the upper and right-hand sides tended to turn yellow and red (Figure 4b), indicating that there is a risk of high N2O emissions when the total N input or irrigation rate is higher.
The soil NO3− concentration and N2O emissions of single-season greenhouse vegetables were found to depend on fertilization and water management (Figure 5). Compared with no nitrogen management, the Cov. and Opt. treatments increased the soil NO3− concentration by 6.89 and 4.43 times, and increased N2O emissions by 7.63 and 4.44 times, respectively. Compared with chemical nitrogen management, MF reduced the soil NO3− concentration by 0.10 times and increased N2O emissions by 0.19 times. SF increased the soil NO3− concentration by 0.19 times and reduced N2O emissions by 0.16 times. MSF increased the soil NO3− concentration and N2O emissions. Compared with quick-acting fertilizer, SRF reduced the soil NO3− concentration and N2O emissions by 0.20 and 0.36 times, respectively. NI did not affect the soil NO3− concentration and reduced N2O emissions by 0.31 times. Bioc (biochar addition treatment) increased the soil NO3− concentration by 0.09 times and reduced N2O emissions by 0.16 times. Compared with the conversation irrigation rate, 0.8 W and 0.6 W increased the soil NO3− concentration by 0.65 and 0.80 times, and reduced N2O emissions by 0.14 and 0.11 times, respectively.

3.3. Effects of Soil Physicochemical Properties on Soil NO3− Concentration and N2O Emissions

The results from Spearman’s correlation analysis indicated that the soil NO3− concentration was positively correlated with ST and N, but negatively correlated with pH, OC, and WFPS (Figure 6). N2O emissions showed a positive correlation with pH, OC, TN, AN, and N. In general, there were no significant relationships between the soil NO3− concentration and N2O emissions on the regional scale.
There were positive relationships between the soil NO3− concentration and N2O emissions in higher soil OC, TN, AN, and pH conditions, and in lower soil ST and BW conditions (Table 1). There was no significant relationship between the soil NO3− concentration and N2O emissions in different total N input, irrigation rate, and WFPS conditions.
The responses of the soil NO3− concentration and N2O emissions to the variation in soil pH (OC) were different. We found that the soil NO3− concentration was positively correlated with total N input in both the lower and higher soil OC conditions, but the slope of this relationship was higher in lower OC than in higher (Figure 7A). The soil NO3− concentration was negatively correlated with the irrigation rate in the higher soil OC condition, but there was no significant relationship in the lower soil OC condition. The soil N2O emissions were positively correlated with total N input in both the lower and higher soil OC conditions, but the slope of this relationship was higher in the higher soil OC condition than in the lower. The soil N2O emissions were positively correlated with the irrigation rate in the lower soil OC condition, but no significant relationship was observed in the higher soil OC condition.
The soil NO3− concentration was positively correlated with total N input in both lower and higher pH soil, but the slope of this relationship was higher in lower pH soil than in higher pH soil (Figure 7B). The soil NO3− concentration was negatively correlated with the irrigation rate in higher pH soil, but there was no significant relationship in lower pH soil. The soil N2O emissions were positively correlated with total N input in higher pH soil, but no significant relationship in lower pH soil. There were no significant relationships between the soil N2O emissions and irrigation rate in both lower and higher pH soil.

3.4. Direct and Indirect Effects of Nitrogen and Irrigation Management and Soil Physicochemical Properties on Soil NO3− Concentration and N2O Emissions

The contributions of nitrogen and irrigation management and basic soil physicochemical properties to the soil NO3− concentration and N2O emissions were observed from the SEM results (Figure 8). The total N input (λ = 0.29) directly affected the soil NO3− concentration and the basic soil physicochemical properties indirectly affected the soil NO3− concentration by complex ST and WFPS responses. The total N input (λ = 0.55) rather than the irrigation rate, or the basic soil physicochemical properties (λ = 0.28) and ST (λ = 0.19), had the strongest direct effect on N2O emissions. The basic soil physicochemical properties directly affected soil N2O emissions (λ = 0.28) and also indirectly affected soil N2O emissions by complex ST and WFPS responses.

4. Discussion

Studies based on meta-analysis showed that with the increase in nitrogen application, both soil NO3− concentration and N2O emissions have experienced a significant increase trend [26,27,28], which is similar to the results of this study. In addition, this study found that the soil NO3− concentration presents a quadratic curve with the increase in irrigation rate. The main reason may be that with the stable nitrogen input, an appropriate increase in the irrigation rate can promote NO3− migration from shallow soil (~10 cm) to the root layer (~20 cm), thereby reducing the gaseous loss of nitrogen in shallow soil through nitrification and denitrification, ammonia volatilization, etc., increasing the NO3− concentration in 0–20 cm soil. When the irrigation rate is increased to a certain extent, the continued addition of excessive water causes NO3− in 0–20 cm soil to migrate to deeper soil with water, resulting in a decline in NO3− concentration in 0–20 cm soil. The study on greenhouse cucumbers also showed that farmers’ conventional irrigation management with a large amount of water resulted in a low NO3− concentration in the surface soil (0–30 cm) and a high NO3− leaching in the soil layer below 100 cm [29]. Drip irrigation management with 60% water of farmers’ conventional irrigation management had less leaching and a relatively higher NO3− concentration in the surface soil [29]. However, in this study, the effect of the irrigation rate on N2O emissions was not significant. Studies on greenhouse cucumbers also showed that when the soil was kept at an optimal moisture level, soil N2O emissions were not sensitive to changes in the soil water content, and the effect of irrigation on N2O emissions was often masked by nitrogen fertilizer [30,31]. In addition, this study showed that soil physical and chemical properties, such as soil organic matter, pH, nitrogen concentration, etc., significantly affect N2O emissions, which may also mask the effect of irrigation on N2O emissions [32,33]. In 2021, China consumed over 42 million metric tons of fertilizers, nearly 30% of the global total. This extensive use is driven by intensive agricultural practices to meet high food production demands, but it also leads to significant environmental impacts. This study found that the maximum nitrogen fertilizer use reached 1600 kg, indicating that there is a large space for optimizing nitrogen fertilizer use in China. To sum up, when the amount of nitrogen application and irrigation water are controlled within a certain range, both the NO3− concentration and N2O emissions can be reduced.
This study found that different types of organic fertilizers have varying effects on soil NO3− concentration and N2O emissions. This may be related to differences in the chemical composition of manure and straw. Under typical high-temperature conditions in greenhouse vegetable systems, manure decompose, releasing large amounts of exogenous C and N throughout the vegetable growth period. This creates favorable conditions for nitrification and denitrification reactions involving microorganisms, thereby promoting soil N2O emissions. Compared to chemical fertilizers, the partial replacement of chemical fertilizers with manure decreased the soil NO3− concentration at harvest (Figure 5). Other studies also showed that compared to rapidly available nitrogen fertilizers, manure released nutrients slowly and reduced the soil NO3− concentration [34], while the decomposition and conversion rates of C and N from straw are relatively slow throughout the vegetable growth period, resulting in lower N2O emissions which facilitated the accumulation of the soil nutrient pool, thus increasing the soil NO3− concentration during the harvest period [35,36]. Slow-release nitrogen fertilizer can significantly reduce the soil NO3− concentration and N2O emissions, which is similar to other studies [37,38]. In addition, this study and other studies also showed that the addition of nitrification inhibitors or biochar significantly reduced soil N2O emissions [39,40]. The reason for the increase in soil NO3− concentration with the application of biochar may be that biochar has a better soil water-holding capacity, developed pore structure and a huge specific surface area, and directly adsorbs nitrogen in the soil through physical and chemical adsorption, thus reducing the total NO3− leaching amount. Therefore, the soil NO3− concentration in the surface soil can be increased [41].
Based on the response of soil NO3− concentration and N2O emissions to basic soil environmental factors, basic soil environmental factors were divided into four categories: (1) Factors that have no significant influence on either the soil NO3− concentration or N2O emissions, including BW. This might be because the effects of the basic soil bulk density on soil NO3− concentration and N2O emissions are masked by nitrogen and irrigation management. (2) Factors that only significantly affected N2O emissions, including basic soil TN and AN. The reason may be that the basic soil TN and AN provide nitrogen sources for N2O emissions during the whole growth period. The surface soil NO3− concentration at harvest was greatly affected by nitrogen and irrigation management during growth, which masked the influence of basic soil TN and AN on the NO3− concentration. (3) Factors that only significantly affect the NO3− concentration, including ST and WFPS. Relevant studies have shown that a higher soil temperature tends to promote soil N2O emissions [40,41]. However, this study showed that ST had no significant effect on N2O emissions, which may be mainly due to the relatively stable soil temperature in greenhouses, and the difference in N2O emissions caused by the change in temperature was not significant. A higher soil temperature has a significant positive effect on NO3− concentration. This may be due to the constant high temperatures in greenhouses when irrigation is paused, which cause strong soil evaporation. This results in water from deeper soil moving to the surface, carrying NO3− with it and increasing its concentration in the surface soil [42]. The greater the WFPS in the surface soil, the more NO3− leaching is accelerated, so WFPS is negatively correlated with the surface soil NO3− concentration. The negative correlation between ST and WFPS also indicates that the higher the temperature, the lower the water concentration of the surface soil, and the higher the accumulation of NO3− in the surface soil. (4) Factors that affect both are significant, including soil OC and pH. Soil OC has significant negative and positive effects on the NO3− concentration and N2O emissions, respectively. The main reason may be that soil with a high organic matter provides more C and N, along with suitable soil structure and mechanical properties. On one hand, this enhanced the fixation of nitrate nitrogen by soil microorganisms and plant uptake reduces the accumulation of soil NO3− to a certain extent [43]. On the other hand, it supports nitrification and denitrification reactions involving microorganisms, thereby promoting soil N2O emissions [34]. The soil pH has significant negative and positive effects on the NO3− concentration and N2O emissions, respectively. The main reason may be that the excessive application of nitrogen fertilizer in greenhouse soil leads to a large accumulation of nitrate nitrogen in the topsoil and aggravates soil acidification. Therefore, the low pH in greenhouse soil is often accompanied by a high NO3− concentration [44]. pH affects the formation and emissions of N2O mainly by influencing the activity of nitrifying and denitrifying bacteria. In the range of pH 5.6~8.6, the soil pH is significantly positively correlated with N2O emissions [30]. This study shows that there is a significant positive correlation between the soil NO3− concentration and N2O emissions under the condition of specific soil physicochemical properties. In this case, the denitrification process in which NO3− participates may be the main process affecting N2O emissions. Relevant studies have shown that there is a significant positive correlation between the denitrification microbial population abundance and soil organic carbon when the soil OC is high [45]. In addition, soil OC has a significant negative correlation with BW and ST, and a significant positive correlation with TN, AN and pH. Therefore, under the condition with higher greenhouse soil OC, TN, AN, pH and lower BW and ST, there is a risk of high NO3− concentration and N2O emissions of greenhouse soil at the same time.
Many studies have shown that increasing the soil organic matter content combined with proper irrigation and fertilizer regulation could improve and fertilize greenhouse soil [34,35,36]. This study showed that when the soil OC increased from less than 14 g kg−1 to more than 14 g kg−1, the response intensity of the NO3− concentration to the nitrogen input rate decreased, but the response intensity of N2O emissions increased. This may be because the microbial population in high organic carbon soil has a greater demand for carbon and nitrogen than in low organic carbon soil. When nitrogen is reduced equally, the demand for nitrogen in high organic carbon soil is stronger, leading to more competition with N2O for nitrogen sources, thus resulting in a more significant reduction in N2O emissions. In higher soil OC conditions, an increasing irrigation rate could significantly reduce the soil NO3− concentration, while increasing the risk of NO3− leaching and increasing N2O emissions. There was a significant positive correlation between greenhouse soil pH and OC, and the response of the NO3− concentration and N2O emissions to irrigation and nitrogen management under different soil OC values is similar to different soil pH conditions. Compared to conditions with a low OC and pH, when the soil OC exceeds 14 g kg−1 and the pH is above 7.4, an appropriate nitrogen rate is more effective in reducing N2O emissions. Additionally, while increasing irrigation can reduce the soil NO3− concentrations, it also raises the risk of significant NO3− leaching. However, CH4, NH3, and NOx emissions also depend on the same soil environmental factors and are not included in this study. Water and soil management might reduce NO3 concentrations and N2O emissions but increase NOx emissions, leading to pollution swapping. Therefore, a comprehensive consideration of greenhouse gas effects and soil NO3− accumulation or leaching is necessary to provide guidance for sustainable environmental development.

5. Conclusions

In summary, the greenhouse soil NO3− concentration was linearly correlated with the total N input and showed a slight increase before decreasing with the irrigation rate; N2O emissions were exponentially correlated with the total N input but showed no significant relationship with the irrigation rate. There was a risk of a high NO3− concentration when the total N input was high and the irrigation rate was low. Additionally, there was a risk of high N2O emissions when the total N input or irrigation rate was high. Compared to using chemical nitrogen management alone, the combined application of chemical fertilizer with manure or straw, as well as the use of biochar, could either increase soil NO3− concentrations by an average of approximately 0.17 times or N2O emissions by about 0.41 times. In contrast, the application of slow-release fertilizer could concurrently reduce the soil NO3− concentration and N2O emissions by 0.20 and 0.36 times, respectively. Soil NO3− concentration was positively correlated with ST, but negatively correlated with pH, OC, and WFPS. N2O emissions were positively correlated with pH, OC, TN, and AN. When greenhouse soils have a higher OC (>14 g kg−1) and higher pH (>7.4), elevated soil NO3− concentrations and increased N2O emissions often occur concurrently. Compared to conditions with a low OC and pH, when the soil OC exceeds 14 g kg−1 and the pH is above 7.4, an appropriate nitrogen rate is more effective in reducing N2O emissions. Additionally, while increasing irrigation can reduce soil NO3− concentrations, it also raises the risk of significant NO3− leaching. Overall, nitrogen and irrigation management should be tailored to local soil physicochemical properties to concurrently regulate soil NO3− concentrations and N2O emissions in greenhouse environments.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agronomy14071387/s1, Table S1: Effect of fertilizer and irrigation management on the greenhouse soil NO3− concentration and N2O emissions. The final dataset consisted of 427 sets of observations from 49 papers published from 2004 to 2021, including 35 papers that studied both nitrogen fertilizer and irrigation management, and 14 papers that only studied nitrogen fertilizer management.

Author Contributions

Conceptualization, G.W., H.Z., X.Q. and J.W. (Juanjuan Wang); methodology, H.X., K.H., X.Q., G.W. and J.W. (Juanjuan Wang); validation, G.W., X.Q. and J.W. (Jinchuang Wang); investigation, G.W., H.X., K.H., H.Z., X.Q. and J.W. (Jinchuang Wang); data curation, G.W.; draft preparation, G.W., J.W. (Jinchuang Wang) and J.W. (Jinchuang Wang); funding acquisition, J.W. (Juanjuan Wang). All authors have read and agreed to the published version of the manuscript.

Funding

The work was supported by the National Key Research and Development Program (2022YFD1500403, 2017YFD0200107), National Natural Science Foundation of China (32171771), and the Central Public-Interest Scientific Institution Basal Research Fund for International Cooperation Research Program of CATAS (1630042023002).

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. Geographic distribution of the dataset about both the greenhouse soil NO3− concentration and N2O emissions in China. The blue dots represent the geographic location where the data were collected.
Figure 1. Geographic distribution of the dataset about both the greenhouse soil NO3− concentration and N2O emissions in China. The blue dots represent the geographic location where the data were collected.
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Figure 2. Histogram and summary descriptive statistics of measured soil NO3− (A) and N2O values (B), and total N input (C) and irrigation rate (D) in greenhouse vegetables.
Figure 2. Histogram and summary descriptive statistics of measured soil NO3− (A) and N2O values (B), and total N input (C) and irrigation rate (D) in greenhouse vegetables.
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Figure 3. Correlations between the soil NO3− concentration and total N input (A) and irrigation rate (C), N2O emissions, and total N input (B) and irrigation rate (D). The circles represent each observation. The lines were the best-fit regression with a higher r2, and the shaded areas indicated their 95% confidence intervals.
Figure 3. Correlations between the soil NO3− concentration and total N input (A) and irrigation rate (C), N2O emissions, and total N input (B) and irrigation rate (D). The circles represent each observation. The lines were the best-fit regression with a higher r2, and the shaded areas indicated their 95% confidence intervals.
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Figure 4. Effect of total N input and irrigation rate on the soil NO3− concentration (a) and N2O emissions (b).
Figure 4. Effect of total N input and irrigation rate on the soil NO3− concentration (a) and N2O emissions (b).
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Figure 5. The effect size and 95% confidence intervals for the effects of nitrogen and irrigation management on soil NO3− concentration and N2O emissions in different categories including N input rate (Cov. and Opt. mean conventional and optimal nitrogen application, respectively), the form of N input (MF means chemical fertilizer and manure are applied together, SF means chemical fertilizer and straw are applied together, MSF means chemical fertilizer, manure and straw are applied together, SRF means slow-release fertilizer), additive (NI means nitrification inhibitor, Bioc means biochar), irrigation rate (0.8 W and 0.6 W mean 80% and 60% of the conventional irrigation rate). The sample size for each variable is shown on the right-hand side. Vertical dashed lines represent the control values, while dots, triangles, and diamonds indicate the average effect values of each treatment.
Figure 5. The effect size and 95% confidence intervals for the effects of nitrogen and irrigation management on soil NO3− concentration and N2O emissions in different categories including N input rate (Cov. and Opt. mean conventional and optimal nitrogen application, respectively), the form of N input (MF means chemical fertilizer and manure are applied together, SF means chemical fertilizer and straw are applied together, MSF means chemical fertilizer, manure and straw are applied together, SRF means slow-release fertilizer), additive (NI means nitrification inhibitor, Bioc means biochar), irrigation rate (0.8 W and 0.6 W mean 80% and 60% of the conventional irrigation rate). The sample size for each variable is shown on the right-hand side. Vertical dashed lines represent the control values, while dots, triangles, and diamonds indicate the average effect values of each treatment.
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Figure 6. Spearman’s correlation relationship between nitrogen and irrigation management (I, irrigation rate; N, total N input), soil physicochemical properties (AN, alkali-hydrolyzed nitrogen; OC, organic carbon; TN, total nitrogen; ST, soil temperature; BW, soil bulk weight; WFPS, water-filled pore space), soil NO3− concentration, and N2O emissions. Different color gradients in the heatmap indicate the Spearman’s correlation coefficients; asterisks denote different significance levels at p < 0.05 (*), p < 0.01 (**).
Figure 6. Spearman’s correlation relationship between nitrogen and irrigation management (I, irrigation rate; N, total N input), soil physicochemical properties (AN, alkali-hydrolyzed nitrogen; OC, organic carbon; TN, total nitrogen; ST, soil temperature; BW, soil bulk weight; WFPS, water-filled pore space), soil NO3− concentration, and N2O emissions. Different color gradients in the heatmap indicate the Spearman’s correlation coefficients; asterisks denote different significance levels at p < 0.05 (*), p < 0.01 (**).
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Figure 7. Correlations between the soil NO3− concentration (N2O emissions) and total N input (irrigation rate) in different soil OC conditions (A), and different soil pH conditions (B).
Figure 7. Correlations between the soil NO3− concentration (N2O emissions) and total N input (irrigation rate) in different soil OC conditions (A), and different soil pH conditions (B).
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Figure 8. Structural equation model (SEM) analysis of multivariate relationships among nitrogen and irrigation management, soil physicochemical properties, soil NO3− concentration, and N2O emissions. Results of model fitting: CHI/DF = 1.995, AGFI = 0.947, CFI = 0.974, RMSEA = 0.048. Numbers near lines represent standardized path coefficients (λ). Asterisks (*) and (**) represent significance levels at p < 0.05 and p < 0.01, respectively. R2 values associated with N2O emissions variables indicate the proportion of variation explained by the model.
Figure 8. Structural equation model (SEM) analysis of multivariate relationships among nitrogen and irrigation management, soil physicochemical properties, soil NO3− concentration, and N2O emissions. Results of model fitting: CHI/DF = 1.995, AGFI = 0.947, CFI = 0.974, RMSEA = 0.048. Numbers near lines represent standardized path coefficients (λ). Asterisks (*) and (**) represent significance levels at p < 0.05 and p < 0.01, respectively. R2 values associated with N2O emissions variables indicate the proportion of variation explained by the model.
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Table 1. Relationship between soil NO3− concentration and N2O emissions under different physicochemical properties. The asterisks denote different significance levels at p < 0.01 (**).
Table 1. Relationship between soil NO3− concentration and N2O emissions under different physicochemical properties. The asterisks denote different significance levels at p < 0.01 (**).
Total N Input (kg hm−2)Irrigation Rate (mm)OC (g kg−1)
≤423.6>423.6≤208.9>208.9≤14>14
n239188199107217207
r0.0539−0.04690.0197−0.0110−0.01730.2789 **
TN (g kg−1)AN (mg kg−1)ST (°C)
≤1.7>1.7≤144>144≤20.4>20.4
n169214118124132166
r−0.02000.2577 **−0.03000.2883 **0.4631 **0.0200
BW (g cm−1)pHWFPS (%)
≤1.3>1.3≤7.4>7.4≤56.3>56.3
n216211120307143146
r0.2898 **−0.04000.02000.2526 **0.13300.1319
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Wang, G.; Xu, H.; Huang, K.; Wang, J.; Zhao, H.; Qian, X.; Wang, J. Concurrent Response of Greenhouse Soil NO3− Concentration and N2O Emissions to Nitrogen and Irrigation Management in China: A Meta-Analysis. Agronomy 2024, 14, 1387. https://doi.org/10.3390/agronomy14071387

AMA Style

Wang G, Xu H, Huang K, Wang J, Zhao H, Qian X, Wang J. Concurrent Response of Greenhouse Soil NO3− Concentration and N2O Emissions to Nitrogen and Irrigation Management in China: A Meta-Analysis. Agronomy. 2024; 14(7):1387. https://doi.org/10.3390/agronomy14071387

Chicago/Turabian Style

Wang, Guiliang, Haojie Xu, Kaiyuan Huang, Jinchuang Wang, Haitao Zhao, Xiaoqing Qian, and Juanjuan Wang. 2024. "Concurrent Response of Greenhouse Soil NO3− Concentration and N2O Emissions to Nitrogen and Irrigation Management in China: A Meta-Analysis" Agronomy 14, no. 7: 1387. https://doi.org/10.3390/agronomy14071387

APA Style

Wang, G., Xu, H., Huang, K., Wang, J., Zhao, H., Qian, X., & Wang, J. (2024). Concurrent Response of Greenhouse Soil NO3− Concentration and N2O Emissions to Nitrogen and Irrigation Management in China: A Meta-Analysis. Agronomy, 14(7), 1387. https://doi.org/10.3390/agronomy14071387

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