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Article

Effects of Water-Saving Management Measures on the Water-Salt Properties of Saline–Alkali Soil and Maize Yield in Ningxia, China

by
Tao Li
1,
Jingsong Yang
2,*,
Rongjiang Yao
2,
Lu Zhang
3,
Wenping Xie
2,
Xiangping Wang
2,
Chong Tang
2,
Wenxiu Li
2 and
Jun R. Yang
1,*
1
College of Agriculture, Yangtze University, Jingzhou 434000, China
2
Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
3
Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, China
*
Authors to whom correspondence should be addressed.
Agronomy 2025, 15(3), 645; https://doi.org/10.3390/agronomy15030645
Submission received: 20 January 2025 / Revised: 2 March 2025 / Accepted: 3 March 2025 / Published: 4 March 2025
(This article belongs to the Special Issue Safe and Efficient Utilization of Water and Fertilizer in Crops)
Browse Figures
Versions Notes

Abstract

:
Background: The Yellow River irrigation area in Ningxia faces spring drought, resalting, severe water resource shortage, and significant water wastage in saline–alkali soils. Objective: To explore the effects of two different improvement measures on maize fresh biomass and the basic physical and chemical properties of saline soil under four irrigation gradients, aiming to provide a theoretical basis for water-saving irrigation in the Yellow River irrigation area of Ningxia while ensuring maize yield. Methods: The experiment designed four irrigation gradients, W1: local conventional water volume (240 mm), W2: 10% water-saving (216 mm), W3: 20% water-saving (192 mm), W4: 30% water-saving (168 mm), and two different soil improvement treatments, a combination treatment of desulfurization gypsum, ETS microbial agent, and biochar (JC), and a combination treatment of desulfurization gypsum, humic acid, and mulching (FS), with a blank control (CK), resulting in 12 treatments in total. Results: The results showed that compared with CK, both JC and FS treatments reduced soil pH, with JC treatment showing a more significant reduction in soil alkalinity than FS treatment. Both JC and FS treatments inhibited the rise in soil electrical conductivity (EC), with JC showing a significantly higher ability to suppress the rise in EC than FS treatment. Both FS and JC treatments improved soil water retention, but in May 2023 during the maize seedling stage, FS treatment had a stronger water retention ability than JC treatment; however, in July at the maize big jointing stage and in September at the maize maturity stage, JC treatment exhibited better water retention ability than FS treatment. Both JC and FS treatments increased maize fresh biomass under four water conditions, but under WI and W2 conditions, there was no significant difference in the ability of JC and FS treatments to increase maize fresh biomass. Under any irrigation condition, the ability of JC treatment to improve WUE is higher than that of FS treatment. Under W3 and W4 conditions, JC treatment significantly outperformed FS treatment in increasing maize fresh biomass yield. Additionally, under W3 irrigation conditions, using JC treatment not only achieved greater water-saving goals but also prevented crop yield reduction due to water-saving measures. This article can provide a theoretical basis for agricultural irrigation management, especially in the Ningxia Yellow River irrigation area of China. It can help ensure crop yields while protecting the ecological environment and promoting sustainable agricultural development.

1. Introduction

Saline–alkali land refers to land that contains excessive soluble salts [such as sodium chloride (NaCl), sodium sulfate (Na2SO4), calcium chloride (CaCl2), etc.], which directly inhibits or harms plant growth [1]. Food is critical to national well-being, and food security is a crucial foundation of national security. The most fundamental way to safeguard national food security is to protect arable land [2]. According to the 2019 National Cultivated Land Quality Bulletin [3], the national average cultivated land quality grade is 4.76 (The average score derived from a comprehensive evaluation of arable land based on a certain grading standard. The grading system is divided into 10 levels, with level 1 being excellent and level 10 being poor.), with medium- and low-grade land accounting for 68.8%. To address this, the 2023 Central No. 1 Document (https://www.lswz.gov.cn/html/xinwen/2023-02/13/content_273655.shtml, accessed on 30 January 2025) proposed to continue strengthening the construction of high-standard farmland, which includes the “pilot comprehensive development and utilization of saline land and other arable land reserve resources” [4]. The Ningxia Yellow River Irrigation Area has a history of more than two thousand years of irrigation and farming. Due to its unique geographic environment and climatic conditions, soil salinization has always been a primary limiting factor for agricultural production in this area [5]. After the establishment of New China, the party and government have placed great emphasis on the management and improvement of secondary soil salinization within the irrigation area, which is a crucial task [6].
The rainfall distribution in Ningxia is uneven, with more rainfall in the south and less in the north. Under arid and semi-arid climatic conditions, the upward movement of soil water and salt dominates, causing the soil to remain in a salt accumulation condition almost year-round [7]. Although the Yellow River irrigation area in northern Ningxia benefits from Yellow River irrigation, the long-term use of irrational irrigation methods, such as flood irrigation and large diversion and drainage systems, leads to a serious waste of surface water [8]. In order to improve the efficiency of freshwater use and effectively prevent secondary salinization of the soil, it is essential to implement water-saving irrigation. Therefore, an in-depth investigation into the water-saving and salt-suppression efficiency of irrigation and leaching water has become an urgent requirement for the sustainable development of saline soils in the Ningxia Yellow River irrigation area [9]. Drip irrigation is an extremely efficient water-saving method, which, when applied according to the water demand patterns of crops in arid and semi-arid regions, can significantly increase crop yield and water use efficiency, while reducing water and nutrient leaching and shallow groundwater pollution [10].
The irrigation water in saline–alkali soils serves two primary purposes: one is to supply the water needed for crop growth, and the other is to leach soil salts. The process of water conservation saves water for leaching salts, not for providing the water required for crop growth. After implementing water-saving measures, the degree of salinization in the soil will deepen due to insufficient water. Under such conditions, additional measures are needed to enhance the rate of soil salt leaching. In China’s efforts to address salinization issues, one breakthrough has been the screening of suitable saline land-specific ameliorants (“Amendments” typically refer to substances that can improve the physical and chemical properties of the soil to enhance soil fertility, improve soil structure, and promote plant growth. Common soil amendments include desulfurized gypsum, humic acid, biochar, microbial fertilizers, and so on). Experimental research has focused on fertilization, real-time field water and salt regulation, the configuration of salt-tolerant plant species, and the organic combination of trees, shrubs, and grasses. Based on these studies, models for the restoration of three types of saline wastelands—salinization, alkalization, and saline–alkalization—have been proposed [11]. Therefore, this study selects several commonly used saline–alkali land amendments in Ningxia for investigation. In 2015, Li Xulin et al. (2015) [12] studied the amelioration effects of different amendments on heavy saline–alkali land near the Yellow River estuary, selecting phosphogypsum, microbial fertilizers, soil life, medicinal fertilizers, and organic fertilizers for testing, and identified the most suitable saline–alkali amendments for the coastal heavy saline–alkali land in that area. Bai Xiaolong et al. (2024) [13] found that desulfurized gypsum effectively reduced soil acidity, pH, and soluble Na+, while improving crop yields. During the process of improving saline–alkali soils, humic acid can adsorb more soluble salts in the soil, and retain a larger number of harmful cations due to its high active groups and large salt exchange capacity. This helps reduce soil salt concentration and the pH of saline soils [14]. Since its discovery, biochar has attracted significant attention for its many advantages, such as improving soil quality and increasing crop yields [15]. It is evident that extensive and mature studies have already been conducted on individual amendments. Therefore, this paper combines several commonly used amendments for saline–alkali soils in Ningxia, exploring the effects of two composite amendments—gypsum and mycorrhizal composite biochar, and gypsum and mulch composite humic acid—on soil characteristics and crop yield to find methods to mitigate the negative effects of water-saving practices on soil salinity. With the aim of providing new in-sights for future soil improvement, this study also explores the impact of different water management measures on maize yield under varying soil salinity conditions, offering valuable references for water resource management in different regions.

2. Materials and Methods

2.1. Overview of the Study Area

The experimental site is located in the Huinong District of Shizuishan City, Ningxia Hui Autonomous Region. It lies between 106°70′ E to 106°80′ E longitude and 39°20′ N to 39°30′ N latitude, situated at the northernmost part of Ningxia. To the east, it borders the Yellow River; to the west, it is backed by the Helan Mountains; and to the north, it adjoins Uhuai City in Inner Mongolia. The region experiences four distinct seasons, with a continental climate. The spring is characterized by dryness and strong winds, with rapid temperature rise. Summers are hot with concentrated rainfall. The autumn is short, with rapid cooling, while winters are dry and cold, with sparse rainfall and snow. There is ample sunshine, large temperature fluctuations, and intense evaporation. The average annual temperature ranges from 2.8 °C to 16.0 °C. Before the experiment, soil samples were collected using the five-point sampling method after spring irrigation and spring plowing, and relevant indicators were tested. Table 1 lists the physical and chemical properties of the topsoil. Although the EC of the tested soil was much less than 4 dS/m, the total salt content was 1.72% and 1.53%, the ESP was 7.63% and 7.35%, and the pH was greater than 8.5. Therefore, according to the FAO (Food and Agriculture Organization) [16] and the standards for soil salinization monitoring in China [17], the tested soil is considered saline–alkali soil. The physical and chemical properties of the topsoil are shown in Table 1.

2.2. Experimental Design

The maize variety used in the experiment was XianYu 1225. Sowing occurred on 22 April 2023, and harvesting was on 20 September 2023. The maize was planted with a plant spacing of 0.3 m and alternating row spacings of 0.4 m and 0.7 m. The irrigation schedule for the maize growing season is shown in Table 2. The experiment consisted of two different soil improvement treatments: a combination treatment of desulfurization gypsum, ETS microbial agent, and biochar (JC), and a combination treatment of desulfurization gypsum, humic acid, and mulching (FS), with a blank control (CK), with four irrigation levels, W1 (240 mm), W2 (216 mm), W3 (192 mm), and W4 (168 mm), for a total of 12 treatments. Each treatment was replicated three times, with each plot having an area of 23.1 m2. The irrigation method used in the experiment was drip irrigation, managed using a water and fertilizer integration system. The drip emitters had a flow rate of 2 L/h, with a spacing of 0.3 m between emitters and 1.1 m between drip tapes. The water quantity entering each plot was precisely controlled using water meters and valves, and the valves were closed promptly once the set irrigation quota was reached, ensuring water conservation through efficient drip irrigation. Before sowing, the various amendments were applied uniformly to the soil surface at the specified rates and then incorporated into the soil using a rotary tiller to ensure even mixing. The management practices during maize growth followed the local farming practices. The application rates of the amendments are as follows: desulfurized gypsum 7500 kg/hm2, humic acid 600 kg/hm2, biochar 14,000 kg/hm2, and ETS microbial fertilizer 3600 kg/hm2. The desulfurized gypsum, biochar, and humic acid are from Tianxinyuan Company, Shizuishan, China, while the ETS microbial agent is from ETS Company, Tianjin, China. Mulching refers to covering the ground with plastic film. Due to the high nutrient content of humic acid, it is not suitable to add other organic materials. Therefore, mulching is implemented to improve soil quality. The basic physical and chemical properties of the tested materials are shown in Table 3.

2.3. Sample Collection and Measurement Methods

In mid-May, July, and September (corresponding to the maize seedling stage, tasseling stage, and maturity stage, respectively, as represented by May, July, and September in the figures that follow), three random sampling points were selected from each plot. The soil samples from these three points were mixed evenly, and one-third of the mixture was then used to determine various soil indicators. Since maize roots primarily grow within the 0–40 cm soil depth, and the tillage depth is 0–20 cm, soil samples were collected using a soil auger at two depths: 0−20 cm and 20−40 cm. The collected fresh soil was immediately used for moisture content determination through the drying method. The remaining soil samples were taken back to the laboratory, where they were air-dried and ground. Once the samples could pass through a 10-mesh sieve, they were treated with deionized water for leaching (soil-to-water ratio of 1:5). The leachate was then measured for pH and EC at 25 °C. Additionally, during the tasseling stage in July, maize plant height and chlorophyll content (SPAD) were also measured.

2.4. Maize Yield Measurement Method

The yield (kg/hm2) is calculated using the formula:
yield = individual plant yield × number of plants per hectare
Water use efficiency (g/kg) is calculated using the following formula:
WUE = yield/amount of water
To eliminate the impact of maize moisture content on fresh biomass, the fresh biomass in this study has been standardized to a moisture content of 65%. The method used first calculated the dry weight of the maize based on its moisture content, and then adjusted the moisture content to 65% to calculate the fresh biomass. For each plot, three sample areas were selected for uniform sampling. The total maize weight in each sample area was divided by the number of maize plants within the sample area to obtain the average weight of an individual maize plant. The average individual plant weight from the three sample areas was then used to determine the average plant weight for the plot. The number of plants per hectare was estimated by extrapolating from the plant count within each plot.

2.5. Measurement Methods for Each Indicator

The methods for determining soil parameters are referenced from “Soil Agrochemical Analysis” [17] and briefly summarized as follows: soil moisture content was measured using the drying method. Soil pH and electrical conductivity (EC) were measured using a pH meter and conductivity meter on a 1:5 soil–water extract, with a measurement temperature of 25 °C. The pH meter and conductivity meter used are both manufactured by Leici, Shanghai, China, with models PHS−3C and DDS−307A, respectively. Total soil salt content was determined using the residue drying-mass method, with a soil–water ratio of 1:5 for the extract; soil CEC was determined using the sodium acetate-flame photometric method; ESP was calculated based on the ratio of exchangeable sodium to CEC; SAR was calculated as the ratio of Na+ concentration to the square root of the average concentration of Ca2+ and Mg2+ in the 1:5 soil–water extract; and chlorophyll content (SPAD) was measured using a chlorophyll meter. The chlorophyll meter used is manufactured by Harucn, Shenzhen, China, model SPAD-502Plus. Plant height and fresh biomass were measured using sampling methods. Three 1 m2 sample areas with uniform maize growth were selected in each experimental plot to measure maize plant height and SPAD values.

2.6. Data Processing and Analysis

The experimental treatments were measured in triplicate samples, and the average values were calculated for each treatment. All data were processed and analyzed using Microsoft Excel 2010. Correlation and statistical analyses were performed using SPSS 27.0 software, and the graphs were created with Origin 2025. To assess the basic physicochemical properties of the soil and other general indicators, a two-factor analysis was first conducted to determine which factor played the primary role and whether there was any interaction between the two factors. The Least Significant Difference (LSD) test was used to evaluate the significance of differences between treatments at p < 0.05. For soil electrical conductivity (EC) analysis, the soil EC after applying the amendments was set as 1, and the increase in soil EC after maize harvest for each treatment was compared.

3. Results and Analysis

3.1. Effects of Two Different Amelioration Measures on Soil pH in Different Soil Layers Under Different Water Conditions

The results of the two-factor analysis showed that irrigation conditions only significantly influenced the soil pH at the 0−20 cm and 20−40 cm soil layers during the maize seedling stage. In contrast, the application of different amelioration measures had a highly significant effect on soil pH at both the 0−20 cm and 20−40 cm soil layers throughout the entire maize growing season (for detailed results, see Table 4). The soil pH values at the 0−20 cm depth for each treatment under different irrigation conditions over the entire growing season are shown in Figure 1a. In the four irrigation conditions, soil pH increased from the seedling stage to the booting stage, but then decreased from the booting stage to maturity. At the same time across the four irrigation conditions, there were no significant differences in soil pH among the treatments. However, based on numerical values, it can be observed that the soil pH under the JC treatment was lower than under the FS treatment and CK, while the soil pH under FS was higher than under JC but lower than CK. This suggests that both the JC and FS treatments have the ability to lower soil pH, with the JC treatment having a stronger capacity to reduce soil pH than the FS treatment. This phenomenon may be explained by the fact that spring irrigation before maize planting reduces soil pH to a lower level. However, after planting maize, drip irrigation is used, which does not provide sufficient water for leaching the salt-alkali obstacles. Additionally, from the seedling stage to the booting stage, direct sunlight increases the surface temperature, causing upward movement of soil water, and leading to more evident alkalization. As a result, although acidic amendments were applied, their ability to reduce pH was outweighed by the pH increase caused by the alkalization. After the booting stage, maize canopy coverage increased significantly, preventing direct sunlight from reaching the soil and reducing the upward movement of soil water. At this point, the leaching rate of salts and alkalis was greater than the accumulation rate, leading to a decrease in soil pH.
Soil pH values at the 20−40 cm depth for each treatment during the three growth stages under different irrigation conditions are shown in Figure 1b. In the four irrigation conditions, at the same time, no significant differences in soil pH values were observed between treatments. However, based on the values, it is clear that the soil pH under the JC treatment was lower than under the FS treatment and CK, while the pH under FS was higher than under JC but lower than CK. This further supports the conclusion that the JC treatment has a stronger ability to reduce soil pH than the FS treatment.

3.2. The Effect of Two Different Amelioration Measures on Soil EC in Different Soil Layers Under Different Watering Conditions

After the addition of materials, both JC and FS treatments lead to a significant increase in soil electrical conductivity (EC). Firstly, the materials themselves carry a large amount of electrolytes. Secondly, during the period from the initial EC measurement to the start of planting, salts will re-accumulate on the soil surface. These two factors together contribute to the increase in soil EC. Therefore, the soil EC at harvest time is compared with the soil EC immediately after the materials were added. The increase in soil EC for each treatment is calculated to reflect the inhibitory effect of each treatment on the increase in salinity.
The ratio of soil EC increase for each treatment in the 0−20 cm soil layer under different watering conditions is shown in Figure 2a. Under the W1 and W2 conditions, the EC increase ratio of the JC treatment is less than 0, significantly lower than that of the FS and CK treatments. Under the W3 and W4 conditions, the EC increase ratios of all three treatments are greater than 0, but the EC increase ratio of the JC treatment is still significantly lower than that of the FS and CK treatments. The EC increase ratio of the FS treatment is significantly higher than that of the JC treatment, but lower than that of CK.
The ratio of soil EC increase for each treatment in the 20−40 cm soil layer under different watering conditions is shown in Figure 2b. Under all four watering conditions, the EC increase ratio of the JC treatment is significantly lower than that of both FS and CK treatments. The EC increase ratio of the FS treatment is significantly lower than that of CK, but higher than that of the JC treatment. Additionally, the increase ratio of soil EC in the 20−40 cm soil layer is significantly higher than that in the 0−20 cm soil layer. This phenomenon suggests that, under all four watering conditions, both the JC and FS treatments can effectively suppress the rise in soil EC. However, the ability of the JC treatment to inhibit the increase in EC is significantly higher than that of the FS treatment.

3.3. The Effect of Two Different Amelioration Measures on Soil Moisture Content in Different Soil Layers Under Different Watering Conditions

The results of the two-factor analysis show that both different watering conditions and different amelioration measures have a highly significant effect on soil moisture content in the 0−20 cm and 20−40 cm soil layers during the growth of maize. Furthermore, there is a highly significant interaction between different watering conditions and amelioration measures in the 0−20 cm soil layer during the big-joint-leaf stage and in the 20−40 cm soil layer during the seedling stage. There is also a significant interaction in the 20−40 cm soil layer during the big-joint-leaf stage (specific analysis results are shown in Table 4). The soil moisture content for each treatment during the full growth period in the 0−20 cm and 20−40 cm soil layers is shown in Figure 3a,b. During the seedling stage, under the same watering condition, the soil moisture content in the FS treatment is higher than that in the JC treatment. However, the difference in soil moisture content between FS and JC treatments is not significant. In the 0−20 cm soil layer, there is no significant difference in soil moisture content between FS, JC, and CK treatments, whereas in the 20−40 cm soil layer, the soil moisture content in FS and JC treatments is significantly higher than that in the CK treatment.
During the big-joint-leaf stage and at maturity, in both the 0−20 cm and 20−40 cm soil layers, the soil moisture content in the JC treatment is significantly higher than that in the FS treatment, and the soil moisture content in the FS treatment is significantly higher than that in the CK treatment. This phenomenon indicates that both FS and JC treatments can maintain soil moisture. However, during the seedling stage, the ability of the FS treatment to maintain soil moisture is stronger than that of the JC treatment. During the big-joint-leaf stage and at maturity, the ability of the JC treatment to maintain soil moisture is stronger than that of the FS treatment.

3.4. The Effect of Two Different Amelioration Measures on Maize Plant Height and SPAD During the Big-Joint-Leaf Stage Under Different Watering Conditions

The results of the two-factor analysis show that both different watering conditions and different amelioration measures have a highly significant effect on maize plant height and chlorophyll content (SPAD). There is no interaction between watering conditions and amelioration measures on maize plant height, but there is a significant interaction between these factors for chlorophyll content. The plant height and SPAD of each treatment during the big-joint-leaf stage under different watering conditions are shown in Figure 4. The degree of water-saving is significantly negatively correlated with maize fresh biomass, meaning that as the water-saving degree increases, both maize plant height and SPAD decrease. In the FS treatment, maize plant height and SPAD are both significantly higher than those in the JC treatment and the CK treatment. In contrast, maize plant height in the JC treatment is significantly lower than that in the CK treatment, while the SPAD in the JC treatment shows no significant difference compared to CK. In conclusion, the FS treatment is more beneficial to maize growth from the seedling stage to the big-joint-leaf stage. This is because, during this period, the temperature is not very high, but the FS treatment is more effective at maintaining soil temperature compared to the JC treatment. Within a reasonable range, higher temperatures are more suitable for maize growth.

3.5. The Effect of Three Different Amelioration Measures on Maize Fresh Biomass and WUE Under Different Watering Conditions

Since the local maize harvesting method is silage, where the entire above-ground portion of the maize is harvested, the maize fresh biomass is equivalent to the maize yield. The results of the two-factor analysis show that both watering conditions and amelioration measures have a significant effect on maize fresh biomass. Additionally, there is a highly significant interaction between watering conditions and amelioration measures.
The maize fresh biomass for the three different treatments under different watering conditions is shown in Figure 5. The degree of water-saving is significantly negatively correlated with maize fresh biomass, meaning that as the degree of water-saving increases, maize fresh biomass decreases. Compared to the W4 condition, the fresh biomass under the CK, JC, and FS treatments in the W1 condition is higher by 5.1%, 13.3%, and 14.4%, respectively.
Under the W1 and W2 conditions, the JC treatment has the highest maize fresh biomass, at 109,762 kg/hm2 and 100,654 kg/hm2, respectively. The FS treatment’s maize fresh biomass is significantly higher than that of the CK treatment, but lower than that of the JC treatment. However, the difference between the FS and JC treatments is not significant. Under the W3 and W4 conditions, the JC treatment’s maize fresh biomass is significantly higher than that of the CK and FS treatments, while the FS treatment’s fresh biomass is higher than that of the CK treatment, though the difference is not significant. Furthermore, under the W3 condition, there is no significant difference in maize fresh biomass between the JC and FS treatments and the CK treatment under the W1 condition. Under the W3 condition, the fresh biomass of the JC and FS treatments is 95,396 kg/hm2 and 93,455 kg/hm2, respectively, while the fresh biomass of the CK treatment under the W1 condition is 95,018 kg/hm2. This suggests that the JC treatment results in higher maize fresh biomass compared to CK, while the FS treatment’s fresh biomass under the W3 condition is lower than that of the CK under the W1 condition.
The water use efficiency of each treatment under different water conditions is shown in Figure 6. From the figure, it can be seen that water use efficiency is positively correlated with the degree of water-saving, with the lowest water use efficiency observed under the W1 condition. Under the same water conditions, the water use efficiency of JC is consistently the highest, while the water use efficiency of CK is consistently the lowest, indicating that both JC and FS can improve water use efficiency, but JC is more effective in enhancing water use efficiency than FS.

4. Discussion

4.1. Impact of Different Amelioration Measures Under Varying Water Availability Conditions on the Physicochemical Properties of Saline–Alkaline Soil

The leaching effect of soil salinity is closely related to the amount of irrigation water used. Within an appropriate irrigation range, the greater the irrigation volume, the more effective the leaching of soil salinity. In arid and semi-arid regions, using leaching irrigation during the non-growing season (autumn irrigation) is an effective way to control soil salinity under drip irrigation [18]. However, due to water scarcity in the study area, saving irrigation water is an urgent task. After implementing water-saving measures, the amount of water available for leaching salt from the soil is insufficient, leading to an increase in soil salinity. Therefore, amelioration measures need to be applied to reduce water consumption without exacerbating soil salinity.
Desulfurization gypsum, primarily composed of CaSO4 and CaSO3, can replace Na+ ions in the soil, thereby reducing soil alkalinity and lowering soil pH. The amount of desulfurization gypsum applied is directly proportional to the extent of soil pH reduction. The more gypsum applied, the better the improvement of soil pH in saline–alkaline soils [19]. In this study, both FS and JC treatments consistently resulted in lower soil pH across all maize growth stages compared to the CK treatment. Additionally, the JC treatment showed a stronger pH reduction effect than the FS treatment, indicating that both treatments are effective in lowering soil pH, with JC being more effective in reducing soil alkalinity.
Under gypsum application, both the saturated extract and the 1:5 soil–water ratio extract electrical conductivity (EC) increase with gypsum addition [20]. Although a biochar addition introduces electrolytes into the soil, it helps to reduce the concentration of harmful salt ions in the soil solution, as well as the Sodium Adsorption Ratio (SAR), thus enhancing both root and shoot biomass of maize [21]. The addition of humic acid increases soil EC, but continuous leaching can effectively improve the soil pH and reduce the concentration of Na+, Ca2+, Mg2+, and K+ [22]. Microbial inoculants, while inevitably increasing soil EC due to new electrolytes, rapidly restore and rebuild the soil microenvironment and root ecosystem, promoting the formation of granular structures that inhibit salt return by blocking capillary pathways. This study also used these materials in combination to ameliorate saline–alkaline soil.
In this study, the EC of JC and FS treatments was higher than that of CK across all four water conditions. However, the EC growth rate analysis revealed that both JC and FS treatments significantly suppressed EC increase in saline–alkaline soils. Moreover, JC treatment had a significantly lower EC growth rate than FS treatment. Under W1 and W2 conditions, JC treatment notably reduced EC in the 0-20 cm soil layer, suggesting that both JC and FS treatments, while introducing new electrolytes, can still suppress EC increases due to salt return. Furthermore, JC treatment is significantly more effective at inhibiting EC growth than FS treatment.
Biochar has a highly developed porous structure, providing a large surface area that can adsorb substantial amounts of water [23]. The oxygen-containing functional groups in biochar reduce surface net negative charge, increase porosity, and enhance adsorption capacity, which helps to retain moisture and improve soil water-holding capacity, thereby reducing water and nutrient losses [24]. Therefore, the application of biochar improves soil moisture and nutrient retention and increases soil infiltration capacity [25]. The beneficial microorganisms in microbial inoculants secrete sticky substances like polysaccharides, which can bind soil particles together to form aggregates. These aggregates create larger pores that increase soil aeration and help retain moisture, thus reducing water loss [26]. Microbial inoculants, a new class of multifunctional formulations enriched with nanoscale biological agents, are known for their strong water absorption, rapid absorption rate, and excellent water-holding capacity [27]. Humic acid, an organic colloid, also binds soil particles, forming stable aggregates that enhance soil water retention [28]. Mulching has a barrier effect that slows vertical evaporation, significantly reducing overall evaporation [29]. Additionally, research by Li et al. showed that mulching can increase soil moisture content and temperature in the 0-15 cm soil layer [30]. Thus, this study combined these materials to enhance soil water retention and mitigate the negative effects of water-saving practices on saline–alkaline soils.
The results indicate that under W1, W2, and W3 conditions, the soil moisture content in the 0−20 cm layer of the JC treatment is significantly higher than that of CK, while FS treatment has lower soil moisture content than JC, but still significantly higher than CK. In the 20−40 cm layer, the soil moisture content in JC treatment is significantly higher than CK under W1, W3, and W4 conditions, and FS treatment has lower moisture content than JC but significantly higher than CK. During the grain filling and maturity stages, JC treatment consistently shows higher soil moisture than both CK and FS treatments, while FS and CK do not differ significantly. These findings indicate that both JC and FS treatments significantly improve soil water retention, and under varying water conditions, JC treatment exhibits stronger water retention ability, consistent with the findings of Bai et al. [31].

4.2. Impact of Different Amelioration Measures Under Varying Water Availability Conditions on Maize Fresh Biomass

Maize is widely grown in the Ningxia Hetao Irrigation District, and due to climate factors, the soil in winter tends to freeze, making it difficult to till and limiting farming to one season per year. Maize is favored by local farmers due to its higher economic returns compared to wheat and soybeans. There are two methods for harvesting maize: one involves harvesting the grain after maize maturity for human consumption, and the other involves harvesting the entire aboveground part of the maize after the grain filling stage, chopping it with machinery into blocks for longer storage as feed for livestock. This study adopted the second method.
The results indicate that as water-saving measures become more pronounced, the fresh biomass of maize decreases, demonstrating that water scarcity impairs normal biological functions, leading to reduced maize yield [32]. However, due to water resource shortages in the Ningxia Hetao Irrigation District, it is urgent to reduce irrigation water waste. Fortunately, the application of drip irrigation technology combined with other measures has proven to be a positive agricultural model, promoting water conservation, stable yields, and improved quality and efficiency across the country [33]. Therefore, this study combined water-saving drip irrigation with soil ameliorants to identify an optimal irrigation volume that meets water-saving goals without reducing maize yield.
The study found that under all four water conditions, the fresh biomass of maize in both JC and FS treatments was significantly higher than that of CK. Under W1 and W2 conditions, the fresh biomass of JC treatment was slightly higher than that of FS treatment, but the difference was not significant. Under W3 and W4 conditions, JC treatment significantly outperformed FS treatment in terms of fresh biomass. Additionally, under W3 conditions, the fresh biomass of JC treatment was not significantly different from CK treatment under W1 conditions. These results suggest that both JC and FS treatments can significantly improve maize fresh biomass under all water conditions. However, under W1 and W2 conditions, the ability of JC and FS treatments to increase fresh biomass is similar, as both treatments can maximize the production benefits when water is sufficient. In contrast, under W3 and W4 conditions, JC treatment shows significantly higher biomass production than FS treatment, as JC treatment performs better in leaching salts under water-deficient conditions. By calculating the WUE of each treatment, it can be seen that under all water conditions, both JC and FS treatments can improve WUE, with the WUE of the JC treatment always being higher than that of the FS treatment. This indicates that the ability of the JC treatment to improve WUE is greater than that of the FS treatment. Notably, under W3 conditions, JC treatment produced more biomass than CK under W1 conditions, while FS treatment produced less than CK under W1 conditions. Thus, using JC treatment under W3 conditions can achieve water-saving goals without causing a reduction in crop yield.

5. Conclusions

Both JC and FS treatments have significant effects on improving soil salinity and alkalinity as well as increasing crop yield. However: 1. The effect of JC treatment in reducing soil pH and inhibiting the increase in soil EC is significantly better than that of FS treatment. 2. In May, FS treatment has better water retention than JC treatment, while in July and September, JC treatment outperforms FS treatment in water retention. 3. Under W1 and W2 conditions, there is no significant difference between the abilities of JC and FS treatments to increase maize yield. However, under W3 and W4 conditions, JC treatment significantly outperforms FS treatment. 4. Under W3 conditions, JC treatment achieves greater water-saving goals without reducing crop yield.
The conclusions drawn from this study can provide a theoretical basis for agricultural irrigation management in practice, especially in the Ningxia Yellow River irrigation area of China, where it can help ensure crop yields while protecting the ecological environment and promoting sustainable agricultural development.

Author Contributions

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

Funding

This research was funded by the National Key Research and Development Program of China (2021YFC3201201, 2021YFD1900602). The funder is Ministry of Science and Technology of the People’s Republic of China.

Data Availability Statement

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

Acknowledgments

The authors of this paper would like to express their sincere gratitude to all the faculty and students of the research group led by Jingsong Yang and Rongjiang Yao. at the Institute of Soil Science, Chinese Academy of Sciences, and the research group led by Jun R. Yang. at Yangtze University for their assistance during the experiment.

Conflicts of Interest

The authors declare no conflicts of interest.

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Agronomy 15 00645 g001
Figure 1. Soil pH under different water conditions for each treatment. Note: (a) indicates data from the 0−20 cm soil layer, and (b) indicates data from the 20−40 cm soil layer. Different lowercase letters indicate significant differences among the amendment treatments (p < 0.05).
Figure 1. Soil pH under different water conditions for each treatment. Note: (a) indicates data from the 0−20 cm soil layer, and (b) indicates data from the 20−40 cm soil layer. Different lowercase letters indicate significant differences among the amendment treatments (p < 0.05).
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Figure 2. Soil EC growth rate under different water volume conditions for each treatment. Note: (a) indicates data from the 0−20 cm soil layer, and (b) indicates data from the 20−40 cm soil layer. Different lowercase letters indicate significant differences among the amendment treatments (p < 0.05).
Figure 2. Soil EC growth rate under different water volume conditions for each treatment. Note: (a) indicates data from the 0−20 cm soil layer, and (b) indicates data from the 20−40 cm soil layer. Different lowercase letters indicate significant differences among the amendment treatments (p < 0.05).
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Figure 3. Soil moisture content under different water volume conditions for each treatment. Note: (a) indicates data from the 0−20 cm soil layer, and (b) indicates data from the 20−40 cm soil layer. Different lowercase letters indicate significant differences among the amendment treatments (p < 0.05).
Figure 3. Soil moisture content under different water volume conditions for each treatment. Note: (a) indicates data from the 0−20 cm soil layer, and (b) indicates data from the 20−40 cm soil layer. Different lowercase letters indicate significant differences among the amendment treatments (p < 0.05).
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Figure 4. Maize plant height and SPAD value at the tasseling stage under different water volume conditions for each treatment. Note: Different lowercase letters indicate significant differences among the amendment treatments (p < 0.05).
Figure 4. Maize plant height and SPAD value at the tasseling stage under different water volume conditions for each treatment. Note: Different lowercase letters indicate significant differences among the amendment treatments (p < 0.05).
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Figure 5. Fresh biomass of maize at maturity stage. Different lowercase letters indicate significant differences among soil improvement treatments (p < 0.05).
Figure 5. Fresh biomass of maize at maturity stage. Different lowercase letters indicate significant differences among soil improvement treatments (p < 0.05).
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Figure 6. Water use efficiency of each treatment under different water conditions. Different lowercase letters indicate significant differences among soil improvement treatments (p < 0.05).
Figure 6. Water use efficiency of each treatment under different water conditions. Different lowercase letters indicate significant differences among soil improvement treatments (p < 0.05).
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Table 1. Initial physical and chemical properties of the tested soil.
Table 1. Initial physical and chemical properties of the tested soil.
Soil Depth (cm)pHEC (µS/cm)Total Salt (g/kg)Soil Moisture Content (%)ESP (%)CECCl−SO42−K+Na+Ca2+Mg2+
0~208.65436.241.7219.976.6312.340.511.530.073.400.480.44
20~408.50374.821.5318.896.3512.180.351.510.102.830.360.46
Note: The data are presented as means. Except for pH and indicators with existing units, the units of other indicators are expressed in cmol/kg.
Table 2. Irrigation timing and water volume for maize.
Table 2. Irrigation timing and water volume for maize.
Maize Fertility PeriodDrip TimeIrrigation Water Quantity (mm)
W1W2W3W4
Seedling to big trumpet stage20 May2421.619.216.8
5 June2421.619.216.8
25 June2421.619.216.8
Before and after the big trumpet stage5 July2421.619.216.8
13 July2421.619.216.8
21 July2421.619.216.8
28 July2421.619.216.8
Trumpet to maturity7 August2421.619.216.8
20 August2421.619.216.8
7 September2421.619.216.8
Table 3. Basic physical and chemical properties of the tested materials.
Table 3. Basic physical and chemical properties of the tested materials.
pHEC
(µS/cm)		CEC
(cmol/kg)		C
(g/kg)		N
(g/kg)		P
(g/kg)		K
(g/kg)
desulfurized gypsum6.556623.55.66.94.50.19
biochar6.919292.471041.445.30.13
humic acid6.8413124.823145821.21.16
ETS microbial inoculant6.858732.12514.15.40.15
Table 4. Differences in soil indicators under different variable conditions.
Table 4. Differences in soil indicators under different variable conditions.
0–20 cm Soil Layer20–40 cm Soil Layer
May pHJuly pHSeptember pHMay Moisture ContentJuly Moisture ContentSeptember Moisture ContentMay pHJuly pHSeptember pHMay Moisture ContentJuly Moisture ContentSeptember Moisture Content
Water conditions*nsns*******nsns******
Material treatment************************
Water condition × Material treatment*nsnsns**ns*nsns***ns
Note: In this table, “ns” indicates no significant difference between the treatments and the indicators (p > 0.05). An asterisk (*) denotes a significant difference between the treatments and the indicators (p < 0.05), while two asterisks (**) indicate an extremely significant difference between the treatments and the indicators (p < 0.01).
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Li, T.; Yang, J.; Yao, R.; Zhang, L.; Xie, W.; Wang, X.; Tang, C.; Li, W.; Yang, J.R. Effects of Water-Saving Management Measures on the Water-Salt Properties of Saline–Alkali Soil and Maize Yield in Ningxia, China. Agronomy 2025, 15, 645. https://doi.org/10.3390/agronomy15030645

AMA Style

Li T, Yang J, Yao R, Zhang L, Xie W, Wang X, Tang C, Li W, Yang JR. Effects of Water-Saving Management Measures on the Water-Salt Properties of Saline–Alkali Soil and Maize Yield in Ningxia, China. Agronomy. 2025; 15(3):645. https://doi.org/10.3390/agronomy15030645

Chicago/Turabian Style

Li, Tao, Jingsong Yang, Rongjiang Yao, Lu Zhang, Wenping Xie, Xiangping Wang, Chong Tang, Wenxiu Li, and Jun R. Yang. 2025. "Effects of Water-Saving Management Measures on the Water-Salt Properties of Saline–Alkali Soil and Maize Yield in Ningxia, China" Agronomy 15, no. 3: 645. https://doi.org/10.3390/agronomy15030645

APA Style

Li, T., Yang, J., Yao, R., Zhang, L., Xie, W., Wang, X., Tang, C., Li, W., & Yang, J. R. (2025). Effects of Water-Saving Management Measures on the Water-Salt Properties of Saline–Alkali Soil and Maize Yield in Ningxia, China. Agronomy, 15(3), 645. https://doi.org/10.3390/agronomy15030645

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