Effects of Ditch Water and Yellow River Irrigation on Saline–Alkali Characteristics of Soil and Paddy

Abstract

This study examined the agricultural water resource shortage and abundant ditch water resources in the Yinbei region of Ningxia. The effects of ditch water and Yellow River irrigation on the saline–alkali characteristics of soil and paddy were investigated using field monitoring and indoor detection methods in Pingluo County, Ningxia (106°31′ E, 38°51′ N). In addition to monitoring ditch water, four treatment groups were established: direct ditch water irrigation (T1), mixed ditch water and Yellow River water irrigation (T2), alternate ditch water and Yellow River water irrigation (T3), and irrigation solely with Yellow River water (CK). The results show the following: (1) The salinity of ditch water samples collected from the experimental field during the rice growth period was less than 1.60 g/L, and the pH of the samples was lower than 8.62; thus, they were classified as mildly brackish water. The application of ditch water irrigation did not result in soil saline–alkali aggravation and the accumulation of excessive amounts of heavy metals in soils and paddies in Pingluo County, Ningxia. (2) The rice yields for the CK, T1, T2, and T3 treatments were 10,437.5, 8318.4, 9182.1, and 9016.2 kg/hm², respectively. Compared with Yellow River irrigation, the rice yields for the T1, T2, and T3 treatments were 20.3, 12.1, and 13.6% lower than that of CK, respectively, with minimal differences observed among them. Hence, under the condition of a water resource shortage in the Yellow River region, ditch water can be appropriately applied for mixed or alternate irrigation to ensure food security. This research has revealed the influences of ditch water irrigation on the saline–alkali properties of soil and the heavy metal contents of paddies.

1. Introduction

Ningxia is located in the northwestern inland region of China, where rainfall is scarce. More than half of the province is located in arid and semi-arid zones, and there is a significant difference between the supply of and demand for water resources [1,2,3]. Agricultural water intake in Ningxia makes up about 5.86 billion m³, accounting for 83% of the total water intake in Ningxia [4]. The irrigation area in northern Ningxia is low-lying with strong water retention, making it suitable for rice cultivation [5]. However, it suffers from water shortage problems in respect of the Yellow River region and prominent rice irrigation differences. As an effective measure for alleviating regional water resource problems and ensuring grain production, the rational application of water resources in farmland drainage ditches has attracted increasing attention.

In China, fresh water resources are scarce and unevenly distributed in terms of time and location. The application of poor-quality water such as groundwater and ditch water for irrigation is a hot topic in agricultural research relating to arid regions. The application of shallow underground brackish water for irrigation can not only supply necessary water for crop growth but also decrease groundwater levels [6,7]. Fan (2020) performed ditch soil column-leaching experiments and found that high-salinity water could promote soil flocculation and improve the soil structure. When irrigated water salinity is lower than 3 g/L, the salt in the soil profile is in an equilibrium state, while at salinity levels of above 3 g/L, salt accumulation occurs, mainly in 0–40 cm deep soil layers [8]. While ditch water contains certain amounts of salt, brackish water delivers lower amounts of salt into soil in a short period of time, and an alternative irrigation method involving brackish water and Yellow River water can be used to avoid salinity aggravation in soil [9]. The authors of [9] found that the heavy metal contents of soil after irrigation with reclaimed water did not obviously change compared with those before irrigation; therefore, heavy metal accumulation in soil did not occur in a short time, and the salt content of the surface soil increased while that of the deep soil did not change much. In the coastal saline–alkali areas of Hebei Province, shallow water resources with salt contents lower than 5 g/L could be reasonably employed for the irrigation of winter wheat without causing secondary salinization due to salt accumulation in a short time [10]. However, research has revealed that compared with freshwater irrigation, brackish water irrigation brings in additional salt. Continuous irrigation can cause salt accumulation, damaging the normal growth of crops and affecting their yields over a certain limit [11]. Therefore, the scientific and safe application of brackish water resources is of particular importance. Wang (2019) concluded that irrigation with treated inferior water did not result in heavy metal pollution in rice, and the heavy metal contents of lead, arsenic, and chromium in rice met the requirements of the National Standard for Food Safety (GB 2762-2017) [12,13]. Wang (2022) concluded that different irrigation water sources did not cause soil pollution, and the heavy metal contents of rice grains did not present significant increases. Compliance with the limit requirements of rice pollutants was verified through comparative tests on rice irrigation with clear water from rivers, purified water from ecological ponds, and treated rural domestic sewage [14].

Currently, research in respect of ditch water primarily focuses on monitoring, while studies relating to farmland ditch water emphasize soil infiltration, saline–alkali properties, crop growth, and so on [15]. However, there is a lack of systematic research on water quality monitoring, scientific utilization, and the effects of ditch water on soil and rice in the Pingluo region of the fifth drainage ditch in Ningxia. Hence, in this study, experiments were performed in the rice experimental field of the Pingluo county experimental station (106°31′ E, 38°51′ N) in Ningxia. By monitoring water quality and performing field experiments, the effects of the variations in ditch water quality, direct ditch water irrigation, mixed ditch water and Yellow River water irrigation, and alternate irrigation on soil salinity, heavy metal contents, and rice heavy metal contents were evaluated. These experiments provide a theoretical basis and technical support for the safe utilization of ditch water and rice planting.

2. Materials and Methods

2.1. Overview of Study Area

The experimental field was located in Pingluo county experimental station (106°31′ E, 38°51′ N), Shizuishan City, Ningxia (Figure 1, drawn with ArcGIS 10.2 software). Pingluo County has a long agricultural history, with favorable basic conditions and a sound agricultural industry system, which makes it a representative self-flow irrigation area in respect of the Yellow River. This area has an arid continental climate and is classified as an arid semi-desert saline area in the middle and upper reaches of the Yellow River. The annual average precipitation and evaporation of the area are 185 and 1841 mm, respectively, with rare and unevenly distributed precipitation, mainly from July to September. In this study, the underground water depth was determined to be 1.3~2.0 m. The fifth drainage ditch on the eastern side of the experimental field is considered the main farmland drainage ditch in Pingluo, and its water resources are rich. Before planting, obvious salt spots were observed on the ground surface of each plot of land. According to a surface analysis, the total salt content in the 0–100 cm soil layer was 0.91~4.2 g/kg, and obvious salt spots were observed in local fields with a total salt content of more than 15 g/kg and a soil pH value of 8.17~9.50. In the 0–20 cm soil layer, the soil alkali–hydrolyzed nitrogen level was 49.7 mg/kg, the available phosphorus level was 29.9 mg/kg, the available potassium level was 317.95 mg/kg, the total nitrogen level was 0.79 g/kg, the total phosphorus level was 0.82 g/kg, the total potassium level was 19.5 g/kg, and the organic matter level was 14.83 g/kg. The soil bulk density was 1.4 g/cm³. The soil texture was clay loam; no ${\mathrm{C}\mathrm{O}}_3^{2-}$ was observed in soil salt ions, the cations mainly consisted of Na⁺ and Ca²⁺, the anions mainly included ${\mathrm{S}\mathrm{O}}_4^{2-}$ and ${\mathrm{H}\mathrm{C}\mathrm{O}}_3^{-}$, and the ratio of Cl⁻/${\mathrm{S}\mathrm{O}}_4^{2-}$ was below 0.5. The soil in the experimental area was sulfate saline soil.

2.2. Experimental Design and Implementation Process

Ningjing 47 was adopted as the experimental variety. Based on the unified planting of rice, a random block design was prepared to set up four treatment groups: direct ditch water irrigation (T1), mixed ditch water and Yellow River water irrigation (T2), alternate ditch water and Yellow River water irrigation (T3), and irrigation solely with Yellow River water (CK). The experimental plots were 8.0 m long and 2.0 m wide, each with a 16.0 m² area. High ridges were built between plots and plots were covered with plastic film. Each treatment was repeated five times. In this research, dry rice planting technology was used. This technology enables rice seeds to be directly sown into the field using special machinery, following the application of a base fertilizer when the field is dry, with subsequent irrigation until the field is sufficiently wet for seed germination. Seeds were sown on 30th April, watered on 4th May, and harvested on 4th October. Border irrigation was adopted as the selected irrigation method. Only ditch water was used in the T1 treatment, 1:1 ditch water and Yellow River water mixed irrigation was used in the T2 treatment, ditch water and Yellow River water alternating irrigation was applied in the T3 treatment, and only Yellow River water was used in the CK treatment during the rice growing period. Fertilization and field management were similar in all regions. During the rice growth period, 225 kg/hm² urea, 375 kg/hm² compound fertilizer, 225 kg/hm² diammonium, and 225 kg/hm² ammonium sulfate were used. The total irrigation water quantity for all treatments in the rice growth period except winter irrigation was 1.65 × 10⁴ m²/hm².

2.3. Soil Sample Collection and Determination

In April 2023, soil samples were collected at depths of 0–20, 20–40, 40–60, 60–80, and 80–100 cm from the surface of the experimental area to obtain the soil background value. Soil samples were collected using a ring knife to determine soil bulk density. Ditch water was collected every month from May to August 2023 for inspection, soil and rice samples were collected after rice harvesting in October 2023, and the yield was measured in each district group with uniform growth and an area of 1 m². Samples were collected in triplicate.

Debris was removed from the collected soil samples, and the cleaned samples were air dried, milled, and passed through a 2 mm sieve. The soil water content was determined through the drying method, and the soil bulk density was measured using the ring knife method. The supernatant was fully shaken with a soil-to-water ratio of 1:2.5, and the pH was measured using a multi-parameter Mettler Toledo S220 tester (METTLER TOLEDO, Greifensee, Switzerland). The supernatant obtained from the previous stage was fully shaken at a soil-to-water ratio of 1:5 and was analyzed using a DDS-307A soil conductivity meter (INESA, Shanghai, China); the obtained value was converted to the total salt content [16]. The pH and salinity values of water samples were measured using a pH meter and a conductivity meter, respectively. Soil organic matter was determined according to the potassium dichromate method and alkali hydrolysis nitrogen was measured based on the alkali hydrolysis diffusion method. The available phosphorus and available potassium were determined using the sodium bicarbonate extraction–molybdenum antimony anti-colorimetric and ammonium acetate extraction flame luminosity methods, respectively. Finally, the heavy metal mass fraction was determined via inductively coupled plasma optical emission spectrometry.

2.4. Data Processing and Analysis

Microsoft Excel 2010 was applied for data processing and Surfer 10 was employed for 3D Wireframe drawing. SPSS 17.0 was used for significance tests and correlation analyses.

3. Results

3.1. Water Quality Variations of Gully Water and Yellow River Water

The ditch water pH in the rice growth stage from May to August 2023 ranged from 7.60 to 8.62, with the lowest value observed in June (p ˂ 0.05), and the salinity value ranged from 0.94 to 1.55 g/L. The ditch water salinity and pH values in May were significantly higher than those in other months (Figure 2). Based on the grading standard of water quality and salinity, the farmland drainage ditch water belonged to the category of weak mineralized water and fresh water and could be directly applied for irrigation. During the experiments, the characteristics of Yellow River water were relatively stable, with salinity ranging from 0.41 to 0.51 g/L and pH ranging from 8.06 to 8.23. The Yellow River water pH and salinity values were not significantly different in the time period from May to August (p > 0.05). The irrigation season in this area spans from May to August. During this period, the farmland drained more efficiently, and the quality of ditch water remained relatively good. However, the salinity of ditch water was still higher than that of Yellow River water during the same period (Figure 2). The pH value of Yellow River water was lower than that of ditch water in May, and it was slightly higher than that of ditch water in the other months. The quality of Yellow River water was good, with relatively stable pH and salinity values, thus qualifying it as high-quality irrigation water. The concentrations of suspended matter, zinc (Zn), nickel (Ni), selenium (Se), arsenic (As), mercury (Hg), cadmium (Cd), lead (Pb), and chromium (Cr), as well as the values of the five-day biochemical oxygen demand (BOD), chemical oxygen demand (COD), and anion surface active dose in ditch water were significantly below the thresholds outlined in the Water Quality Standard for Farmland Irrigation (GB 5084-2021) [17] (

Table 1. Water quality physical and chemical properties of ditch water mg/L.

Item	Component Content											Five-Day Biochemical Oxygen Demand (BOD)	Chemical Oxygen Demand (COD)	Anion Surface Active Dose
	Total Nitrogen	Total Phosphorus	Suspended Matter	Zn	Ni	Se	As	Hg	Cd	Pb	Cr
Ditch water	1.8	0.042	2.5	0.01	0.001	None	0.001	None	None	0.001	0.004	4.5	7.5	None
Threshold value	≤2.0 (Class V)	≤0.2 (Class I)	≤80	≤2	≤0.2	≤0.02	≤0.05	≤0.001	≤0.01	≤0.2	≤0.1	≤60	≤150	≤5

Note: Except for the threshold values of total nitrogen and total phosphorus contents in the Surface Water Environmental Quality Standard (GB 3838-2002), other thresholds are the threshold values of paddy field crops presented in the Water Quality Standard for Farmland Irrigation (GB 5084-2021).

). The total phosphorus and nitrogen concentrations in ditch water were 0.042 mg/L and 2.5 mg/L, respectively, which accords with the requirements of the basic project standard of the Surface Water Environmental Quality Standard (GB 3838-2002) [18].

3.2. Effects of Different Treatments on Soil Saline–Alkali Properties

Variations in soil salinity and pH values before planting in April and after harvesting in October are presented in Figure 3 and Figure 4, respectively. Under the effect of the local climate, the salt return was obvious before planting in spring, the surface salt content was the highest (4.6 g/kg), and salt was accumulated on the surface. The soil salt contents of the four treatments were significantly decreased compared with those in spring. The soil salt contents of the 0–20 and 20–40 cm soil layers under CK treatment were 78.7 and 78.9% lower than those before planting, respectively, and that of the 0–100 cm layer was lower than 0.98 g/kg; this was the lowest among all treatments. The soil salinity of the 0–40 cm soil layer treated with T1 was significantly higher than those of other treatments, and that of the soil layer deeper than 40 cm exhibited little difference compared with that before planting (p > 0.05). Compared with other treatments, direct ditch water irrigation increased the surface soil salt content to a certain extent. The soil salt content values for the 0–20 cm soil layer treated with T1 were 90.8, 23.1, and 14.7% higher than those of the CK, T2, and T3 treatments, respectively. The surface soil salt content of the T1 treatment after the first year of rice harvesting was lower than 1.9 g/kg.

Before planting, the pH value was bounded by the 40 cm soil section, the pH value of the 0–40 cm soil layer was below 9.0, and that of the soil layer deeper than 40 cm was higher than 9.0 (Figure 4). The soil pH value increased with the increase in soil depth. After rice harvesting, the soil pH values of the four treatments in the 0–20 cm soil layer were slightly reduced. The pH values of the soil across the four treatments were between 8.2 and 9.5; the pH values of the surface soil were the lowest, with all values below 8.6. All of the pH values presented increasing trends with increasing soil depth (Figure 4), and there were only small differences in soil pH value values among the four treatments (p > 0.05). During the rice growth period, the salt pressure effect was obvious, the average soil salt decrease in the 0–20 cm soil layer for the four treatments was 67.4%, and the pH reduction was less than 6%. The decreased salt and alkali contents in the soil were most obvious in respect of the Yellow River direct irrigation. In addition, direct ditch water irrigation, mixed ditch water and Yellow River water irrigation, and alternate irrigation did not increase the salt and alkali contents in the soil after harvesting. However, direct ditch water irrigation still slightly increased the surface soil salinity.

3.3. Effects of Different Treatments on Soil Heavy Metals

As, Hg, Cd, Cr, and Pb contents in the 0–20 cm soil layer before planting met the thresholds specified in the Secondary Standard for Soil Environmental Quality (GB15618-1995) [19]. The contents of the above heavy metals in the soil treated with T1, T2, and T3 after harvesting were increased. However, they were much lower than the thresholds advised in the Secondary Standard for Soil Environmental Quality (GB15618-1995) (

Table 2. Heavy metal contents in soil, mg/kg.

Item	As	Hg	Cd	Cr	Pb
Before planting	15.53 ± 1.43 ab	0.04 ± 0.01 b	0.13 ± 0.01 a	32.01 ± 3.26 b	15.33 ± 0.82 b
T1	16.87 ± 1.65 a	0.13 ± 0.02 a	0.17 ± 0.01 a	39.74 ± 4.06 a	20.16 ± 1.42 a
T2	16.32 ± 0.96 a	0.09 ± 0.01 ab	0.15 ± 0.01 a	36.23 ± 3.12 ab	18.39 ± 1.06 ab
T3	16.57 ± 1.32 a	0.11 ± 0.02 a	0.14 ± 0.01 a	37.76 ± 2.86 ab	19.75 ± 0.97 ab
CK	15.12 ± 1.13 b	0.05 ± 0.01 b	0.12 ± 0.01 a	32.57 ± 1.68 b	16.17 ± 1.32 b
GB15618—1995	25.0	1.0	0.6	250.0	350.0

Note: Different letters indicate significant differences among different scenarios in one index at 0.05 significance level.

).

No significant differences were observed in Cd contents in any of the treatments compared with levels before planting (p ˃ 0.05). The As, Hg, Cd, Cr, and Pb contents in the CK treatment were the lowest, and there were no significant differences compared to those before planting (p ˃ 0.05). The Hg, Cr, and Pb contents in the soil treated with T1 were significantly higher than those before planting (p ˂ 0.05). Compared with Yellow River irrigation, soil As, Hg, Cr, and Pb contents were increased to a certain extent after ditch water irrigation, but were much lower than the thresholds specified in the Secondary Standard for Soil Environmental Quality. There were no significant differences in the As, Hg, Cd, Cr, and Pb contents between the T2 and T3 treatments (p ˃ 0.05). Hence, direct ditch water irrigation, mixed ditch water and Yellow River water irrigation, and alternate irrigation during the rice growth period did not lead to excessive heavy metal contents in the soil.

3.4. Effects of Different Treatments on Heavy Metals and Paddy Yield

After harvesting, the As, Hg, Cd, Cr, and Pb contents in rice corresponding to the four treatments were all lower than the threshold values specified in the National Standard for Food Safety (GB 2762-2017) (

Table 3. Heavy metal contents and yields of paddies.

Item	Heavy Metal Content (mg/kg)					Yield (kg/hm2)
	As	Hg	Cd	Pb	Cr
T1	0.23 ± 0.09 a	0.006 ± 0.002 a	0.08 ± 0.02 a	0.26 ± 0.07 a	0.37 ± 0.09 a	8318.4 ± 134.7 c
T2	0.15 ± 0.03 a	0.004 ± 0.001 a	0.06 ± 0.01 a	0.21 ± 0.09 a	0.24 ± 0.06 ab	9182.1 ± 128.9 b
T3	0.16 ± 0.04 a	0.005 ± 0.001 a	0.07 ± 0.01 a	0.17 ± 0.04 a	0.21 ± 0.08 ab	9016.2 ± 157.3 b
CK	0.08 ± 0.02 b	0.003 ± 0.001 a	0.04 ± 0.01 a	0.11 ± 0.03 a	0.17 ± 0.07 b	10,437.5 ± 187.5 a
GB2762—2017	0.5	0.02	0.2	0.5	1

Note: Different letters indicate significant differences among different scenarios in one index at 0.05 significance level.

). The Cr content of rice under the T1 treatment was significantly higher than that under the CK treatment (p ˂ 0.05), but no significant differences were observed in respect of the As, Hg, Cd, and Pb contents among the four treatments (p ˃ 0.05). The rice yields of the T1, T2, and T3 treatments were much lower than that of CK (p ˂ 0.05), and the T1 treatment had the lowest rice yield. As mentioned above, the rice yields of the T1, T2, and T3 treatments were 20.3%, 12.1%, and 13.6% lower than that of CK, respectively, while no significant difference was observed between the T2 and T3 treatments (p ˃ 0.05). Ditch water irrigation did not result in excessive heavy metal contents in rice, but ditch water irrigation affected rice yield to a certain extent. In addition, direct ditch water irrigation did not decrease the yield. There was little difference between the effects of mixed ditch water and Yellow River water irrigation and alternate irrigation on the rice yield.

4. Discussion

Brackish water could be reasonably applied for irrigation in arid and semi-arid areas, and the key to this lies in how to make its use efficient, safe, and reasonable [20,21]. In this research, ditch water salinity in the experimental area varied from 0.66 to 1.19 g/L during the rice growth period. Based on the grading standard of water quality and salinity [22], salinity values lower than 1.0 g/L indicate high-quality irrigation water, while a salinity range of 1.0 to 2.0 g/L indicates weakly mineralized water and could be applied for irrigation. Hence, the ditch water in this study belonged to the category of weakly brackish water and fresh water during the rice growth period. From June to August, ditch water salinity was lower than 1.0 g/L, which indicates high-quality irrigation water.

In the Yinbei irrigation area of Ningxia, brackish water with salinity values from 0.94 to 1.55 g/L has been employed for irrigation, and soil desalination was obvious; however, the pH value, salt content, and alkalinity of the soil were higher than those in respect of Yellow River irrigation [23]. Some research works have revealed that irrigation with brackish water with low salinity effectively reduced soil salinity, presenting no significant difference compared with freshwater irrigation [24]. This result might be related to the number of years of brackish water irrigation. Long-term brackish water irrigation increases the surface soil salt content to a certain extent [8], especially in northwestern inland areas, where there is little rain and severe drought. With the increase in brackish water irrigation years, salt can easily accumulate in the soil surface.

In this study, compared with mixed irrigation and alternate ditch water and Yellow River water irrigation, direct ditch water irrigation increased the soil salinity in the 0–40 cm soil layer, which was consistent with the findings of Fan (2020), suggesting that brackish water irrigation increases the upper soil salinity to a certain extent [8]. Although ditch water contains certain amounts of salt, a limited amount of salt is brought in in a short period of time and salt and alkali aggravation can be avoided by alternating between brackish water and fresh water irrigation [9]. This was also proved by the fact that mixed or alternating irrigation with ditch water and Yellow River water did not significantly affect crop yields, and the effects were relatively minor compared with direct ditch water irrigation. However, the brackish water irrigation threshold in the coastal area of China is typically above 3 g/L [10], which is due to the fact that high rainfall and natural precipitation in coastal areas have a certain leaching impact on soil salinity. Ditch water irrigation had a slight influence on soil pH.

Kazuto (2023) found that the introduction of paddy drainage during the irrigation season significantly alters the DOC components in river waters, and irrigation management is strongly linked to the primary production in agricultural channels [25]. Li (2020) found that fully utilizing ditches and ponds as temporary reservoirs in a typical paddy IDU could reduce nitrogen loads from field edges by 39% and phosphorus loads by 28%. Therefore, natural ditches and ponds are recommended to be included in irrigation [26]. Compared with Yellow River water, ditch water contains certain amounts of total nitrogen and total phosphorus, which can complement soil fertility. However, the long-term effects of direct ditch water irrigation on soil health require further verification through long-term tests. If Yellow River water is reliably available, it is recommended to implement mixed or alternate irrigation using both Yellow River water and ditch water.

Eldardiry (2013) found that through brackish water irrigation, excessive salt in water affected normal crop growth. Water containing small amounts of salt stimulates crop growth to a certain extent, and crop quality is improved [27]. Ditch water irrigation brings extra salt into the soil, which interacts with the chemical elements present in the soil and changes the physical and chemical properties of the soil. Under alkaline conditions, the irrigation water salinity is low, the soil aggregate structure is destroyed, and clay particle expansion and dispersion reduce the porosity and permeability of soil, while high-salinity irrigation water increases the flocculation of soil and reduces the expansion and dispersion of clay particles [28]. In this experiment, the heavy metal contents of ditch water conformed to farmland irrigation water quality standards; the soil heavy metal contents after direct ditch water irrigation, mixed ditch water and Yellow River water irrigation, and alternate ditch water and Yellow River water irrigation complied with the requirements of the Secondary Standard of Soil Environmental Quality and did not lead to excessive heavy metal contents in soil. Ditch water irrigation did not result in excessive heavy metal contents in rice, but it affected rice yield to a certain extent. The rice yield under direct ditch water irrigation was the lowest, and there was little difference between the mixed ditch water and Yellow River water irrigation and the alternate ditch water and Yellow River water irrigation in terms of rice yield. Therefore, if conditions allowed, mixed ditch water and Yellow River water irrigation and alternate ditch water and Yellow River water irrigation should be given priority. There is a risk that long-term irrigation with ditch water will increase soil salinity and affect crop yields.

5. Conclusions

(1)

Ditch water salinity from the experimental field was less than 1.60 g/L and its pH value was lower than 8.62 during the rice growth period from May to August in Pingluo County, Ningxia; the water is therefore classified as mildly brackish water suitable for farmland irrigation.

(2)

The application of ditch water irrigation for rice did not lead to soil salinity and alkali aggravation, and the heavy metal concentrations in both soil and rice remained within specified standard values. The heavy metal concentration in soil complied with the requirements of the Secondary Standard of Soil Environmental Quality, while the heavy metal concentration in rice met the requirements of the National Standard of Food Safety.

(3)

The rice yields for the CK, T1, T2, and T3 treatments were 10,437.5, 8318.4, 9182.1, and 9016.2 kg/hm², respectively. Compared with Yellow River irrigation, the rice yields for T1, T2, and T3 treatments were 20.3%, 12.1%, and 13.6% lower than that for CK, respectively, with minimal differences among them.

Therefore, in the case of a water resource shortage in the Yellow River, farmland drainage ditch water can be effectively utilized for mixed ditch water and Yellow River water irrigation or alternate ditch water and Yellow River water irrigation to ensure food security.