Agricultural Water Quality Assessment and Application in the Yellow River Delta

Abstract

Irrigation is the primary agricultural utilization of water resources worldwide, and it produces 36% of the food. The quality of irrigation water influences crop growth and food safety. The coastal river delta region supplies huge area lands for developing agriculture, and the irrigation in this area is composed of many resources for its special location. This study investigated the agricultural water with different resources and evaluated its quality in the Yellow River Delta. The water samples included irrigation water, underground water, and drainage water. The sampling points were designed in the typical areas of Kenli county and Guangrao county in Dongying city, which is the core area of the Yellow River Delta. Through testing the ions composition and the parameters of electrical conductivity (EC), pH, and so on, six evaluation methods were conducted to assess the water quality. The results suggested that the Yellow River water has good quality for irrigation or unconventional water utilization. The high concentration of Na⁺ and Cl⁻ was the primary problem of the water resource. The rainfall was also another water resource supplement in this region. Therefore, developing saline water irrigation incorporated with salt-tolerant crop cultivation is a rational measure for improving coastal agriculture in the Yellow River Delta.

1. Introduction

Agriculture is an important part of the water cycle, and the water utilization in agricultural production is necessary to feed the world’s creatures and provide ecological services [1]. Water for irrigation and crop production causes great pressure on freshwater resources, and the world agriculture consumes about 70% of the fresh water each year [2]. The global demand for water in agriculture will increase as time goes on with increasing population [3]. Irrigation supplies an important support for agricultural development, and China’s food production highly relies on irrigation quality [4]. Optimal utilization of water resources for agricultural production is the serious challenge worldwide [5]. China is one of the most typical countries with severe water shortages, and the lack of freshwater resources has severely affected China’s sustainable development [6]. China is trying to coordinate growing demands for freshwater with excessive renewable water resources for agricultural consumption [7]. Nevertheless, water and land resources are unbalanced in distribution and mismatched in space [8].

Coastal zones are transition environments, and coastal saline agriculture accounts for a large area in China [9]. Yet, the irrigated agriculture in coastal areas is dependent on an adequate water supply of usable quality; thus, the seawater intrusion is a serious problem [10]. Human activity affected coastal water resources and reduced the flows of freshwater to estuary, and enlarging sea intrusion influences further inland. This situation may adversely affect water availability in the coastal area, making the coastal water resources become a worldwide key socio-environmental concentration [11]. Coastal agricultural activities are more unstable than inland agriculture because they should deal with frequent changes in water stresses, salinity, tidal fluctuation, and extreme precipitation [12,13]. Although the water resources are widely distributed in the coastal area, these regions particularly need attention due to the intrusion of saline marine water, pollutants transported from rivers, and agricultural non-point source pollution [14,15,16]. Therefore, the useful water resources for agricultural production account for little in coastal areas, which usually consists of groundwater and river waters. On this basis, to maintain and increase the sustainable yield of crops in coastal areas, developing a rational water use strategy has important practical significance [17].

The Yellow River Delta was formed by the depositional effect of sediment carried by the Yellow River, and the massive mud and sand caused expansion of 20~25 km² per year [18]. The delta occupies 7870 km², and it mostly covers Dongying City and Binzhou City and parts of the cities of Zibo, Dezhou, and Weifang [19]. The typical characteristic of agricultural production in the Yellow River Delta is that there are rich lands, but a fragile ecosystem. The Yellow River Delta region is an important grain-providing base, and it includes many kinds of crop systems, including crop rotation systems, vegetables or fruits systems, understory economy, and rice systems [20]. Although the agriculture has been developed for a hundred years, the low crop yield and the unabundant cropping made it need to pay more attention to improving the productivity in this region. Efforts to increase crop production in salt-affected areas are restricted by the lack of fresh water for irrigation. It is estimated that approximately 47.4% of the land in this area was saline soil, and the salinity content of the estuary wetlands changed between 0.4 g L⁻¹ and 26.7 g L⁻¹ [21]. The Yellow River is usually the only fresh water resource in the Yellow River Delta, where irrigation accounts for 80% of the water consumed from the river, except the rainfall resource [22]. Therefore, it is necessary to use water of lower quality to meet crop water requirements [23]. To avoid problems when using these poor-quality water resources, there must be good guidelines for ensuring that the quality of water available could be used properly.

There are high demands for agricultural water quality objectives in the Yellow River Delta, but demands for significant growth in crop production to satisfy both food supply targets and provide vast quantities of livestock for farmers make these difficult to achieve [24]. The quality of irrigation waters varies in different areas based on how the water resources have been used. The utilization of water for irrigation is lacking, and it hinders the diversity of crops for cultivation in the Yellow River Delta, so it is important to evaluate the irrigation water quality before using it. Water resources in adequate quantity and proper quality are essential to ensure crop production, so it is of great significance to know the current situation of the water quality in this area [25]. Water is one of the most important components for sustaining high agricultural production in the Yellow River Delta, but its quality is intimately related to the development of waterlogging and soil salinity in the irrigation conditions. Furthermore, the concentration and composition of soluble salts in water determines its quality for irrigation. The objectives of this study was to investigate the current water quality situation by various acceptable assessment criteria with different evaluation parameters and analyze the water resources utilization methods in the typical agricultural regions of the Yellow River Delta.

2. Materials and Methods

2.1. Experimental Site

The study area is located in Dongying City (E 118°5′, N 38°15′). The city is the central city of the Yellow River Delta. It consists of three counties, including Guangrao, Lijin, and Kenli, and two districts, including Kenli and Dongying, with a total area of 8257 km² (Figure 1). The city is short of freshwater resources, mainly obtained from the Yellow River. Its average altitude is 5.3 m, and the Yellow River along domestic Dongying City is approximately 138 km. The climate is a sub-humid, warm, temperate, continental monsoon climate. The annual average temperature and precipitation is 13.3 °C and 537 mm, respectively. The average annual evaporation is 1885 mm, and about 206 days in the year are frost-free. The main soil type in the study areas was salinized fluvo-aquic soil following the Chinese Soil Taxonomy, and the land that is suitable for agriculture development is about 52.11%. Maize and wheat were the main crops cultivated in Kenli and Guangrao county, which were planted in summer and winter, respectively. The sown area of maize and wheat in the year of 2021 was 16,981 and 16,867 ha, respectively, in Kenli county and 42,139 and 42,088 ha, respectively, in Guangrao county (Dongying Statistical Yearbook, 2022).

There are mainly three types of water supplying Dongying City, namely, surface water, undergroundwater, and other water resources. The surface water includes pumping water, reservior water, and diverted water. The undergroundwater includes shallow and deep water, and saline water. The other water resources contain rainfall collection and farmland reuse water. The main irrigation method was flood irrigation. The average annual surface and underground water content was 0.47 and 0.23 billion m³, respectively (The annual statistics of Dongying City, 2022).

2.2. Experimental Design

For collecting water resources data, four major kinds of water resources were obtained. They consist of the irrigation water, underground water, drainage water, and rainfall. The rainfall information was obtained from the China Meteorological Data Network (data.cma.cn). The other three types of water resources were extracted by pump in Guangrao county (29 points) and Kenli county (8 points), as illustrated in Figure 1. The water samples were collected by a small peristaltic pump from June 30 to July 10 in 2021.

The main nine ions Na⁺, K⁺, Ca²⁺, Mg²⁺, HCO₃⁻, CO₃²⁻, SO₄²⁻, NO₃⁻, and Cl⁻ of the water samples were measured by ion chromatography (Mettler Toledo Dionex™ ICS-6000, ZRH, Switzerland). The pH value was determined by PHSJ-4A (Leici Company, Shanghai, China). The electrical conductivity (EC) of the water samples was tested by DDSJ-308A (Leici Company, Shanghai, China).

2.3. Water Quality Assessment

The national standard of water quality standard for farm irrigation (GB 5084-2021, China) was used for assessing the effects of water salinity on crops. The primary indicators are listed in

Table 1. The basic control parameters limits for agricultural irrigation water quality.

Parameters	Limiting Value
pH	5.5~8.5
Salt content (mg/L)	1000 (non-saline soil area) 2000 (saline soil area)
Cl− (mg/L)	350

.

For comprehensively assessing the water quality affecting agricultural irrigation, five other assessment methods of the international standards were conducted. They were irrigation coefficient method (

Table 2. Irrigation coefficient method.

Ions Composition	Irrigation Coefficient/Ka
c (Na+) < c (Cl−), NaCl existing	$\mathrm{Ka}=\frac{288}{5\mathrm{c} \left({\mathrm{Cl}}^{-}\right)}$
c (Cl−) < c (Na+) < c (1/2 SO42−)+ c (Cl−), NaCl and Na2SO42− existing	$\mathrm{Ka}=\frac{288}{\mathrm{c}\left({\mathrm{Na}}^{+}\right)+4\mathrm{c} \left({\mathrm{Cl}}^{-}\right)}$
c (Na+) < c (1/2 SO42−)+ c (Cl−), NaCl, Na2SO42−, and Na2CO3 existing	$\mathrm{Ka}=\frac{288}{10\mathrm{c}\left({\mathrm{Na}}^{+}\right)-5\mathrm{c}\left({\mathrm{Cl}}^{-}\right)-9\mathrm{c}\left(\frac{1}{2}{{\mathrm{SO}}_4}^{2-}\right)}$

Note: The c (Na⁺), c (Cl⁻), and c (1/2 SO₄²⁻) are the concentrations of the Na⁺, Cl⁻, and SO₄²⁻, respectively. The unit is mmol/L. When the Ka > 18, the water is fully applicable; Ka = 6~18, applicable; Ka = 1.2~6, not well applicable; Ka < 1.2, the water cannot be used. The irrigation coefficient (Ka) is a standard that reflects the action of sodium salts and is calculated by different empirical formulas according to the relative contents of sodium ions, chloride ions, and sulfate.

), the United States Natural Resources Conservation Service (NRCS) irrigation water quality grading (

Table 3. The NRCS irrigation water quality grading.

Classification of the Water	1	2	3	4	5
Water quality	Very good	Good	Used after dilute	Not well applicable, need good drainage	Cannot be used
EC (mS/cm)	≤0.25	0.25~0.75	0.76~2.00	2.01~3.00	≥3.00

), the sodium adsorption ratio method (

Table 4. The sodium adsorption ratio method.

Parameters	Harmful Water	Harmful Marginal Water	Safer Water	Used Safely
$\mathrm{SAR}=\frac{\mathrm{c}\left({\mathrm{Na}}^{+}\right)}{\sqrt{\frac{\mathrm{c}\left({\mathrm{Ca}}^{2+}\right)+\mathrm{c}\left({\mathrm{Mg}}^{2+}\right)}{2}}}$	>20	15~20	8~15	<8

Note: The c (Na⁺) and c (Cl⁻) are the concentration of the Na⁺ and Cl⁻, respectively. The unit is mmol/L.

), the toxicity level of specific ions (

Table 5. The toxicity level of specific ions assessment.

Degree	Low	Middle	High	Very High
Cl− (mg/L)	≤70	70–140	141–350	≥350
Application status	Suitable for all plants	Sensitive plants are susceptible to damage	Non-sensitive plants damaged	Produce severe environment problems, plants harmed
SAR	1~9	10~17	18~25	≥26
Application status	Careful when used for Na+ sensitive plants	Need infiltration and dilute	Usually not used consistently	Not used

), and the FAO irrigation water quality assessment indicators (

Table 6. The FAO irrigation water quality assessment indicators.

Water Quality Indicators	Parameters	Status of Restricted Utilization
		Non	Light to Moderate	Heavy
Salinity	EC (mS/cm)	<0.7	0.7~3.0	>3.0
Infiltration	SAR	EC (mS/cm)
	0~3	>0.7	0.2~0.7	<0.2
	3~6	>1.2	0.3~1.2	<0.3
	6~12	>1.9	0.5~1.9	<0.5
	12~20	>2.9	1.3~2.9	<1.3
	20~40	>5.0	2.9~5.0	<2.9

).

2.4. Statistical Analysis

All statistical analyses were conducted in SPSS version 19.0 (IBM Company, New York, NY, USA), while all figures were conducted with Origin version 2022 (OriginLab, Northampton, MA, USA).

3. Results

3.1. Agricultural Water Resources

3.1.1. Precipitation

Figure 2 is a plot of the annual precipitation from 2000 to 2022. There was an increase tendency in the recent five years compared to the early years, and the precipitation was unique during consistent years. Furthermore, as shown in Figure 3, the rainfall mainly concentrated between June to October, and the rainfall varied greatly month to month. During December to January, there was almost no rainfall. Therefore, rainfall was a huge water resource, but it needs a useful method to reserve it and prevent extreme precipitation hazards. The extreme rainfall induced inhibition of the maize growth and the farmland waterlogging, and it always occurred in July, which is the important jointing period of the maize, such as in the year 2021 (Figure 3). The regular pattern of rainfall changed sharply in recent years, and it may be affected by the global climate change.

3.1.2. Water Quality Index Parameters

The pH in Guangrao county was higher than that in Kenli county (

Table 7. Water quality index parameter values (mg/L).

Guangrao County					Kenli County
Parameters	Maximum	Minimum	Average	SE	Parameters	Maximum	Minimum	Average	SE
pH	9.22	7.15	8.38	0.48	pH	8.47	6.39	7.60	0.79
EC	15.97	0.95	6.07	3.76	EC	24.49	0.88	7.50	8.70
TDS	7986.00	476.50	3035.08	1881.80	TDS	12,240.00	438.20	3749.14	4350.25
SAR	38.26	3.86	21.88	9.37	SAR	44.30	2.98	16.01	13.74
Cl−	4576.50	50.29	1479.64	1194.28	Cl−	7988.14	98.36	2129.23	2803.69
SO42−	1259.00	38.80	743.51	367.34	SO42−	840.91	129.64	366.59	270.89
NO3−	116.69	0.00	10.05	25.04	NO3−	3.99	0.00	0.82	1.57
Na+	2656.44	96.21	1051.73	689.76	Na+	3370.18	84.95	1052.93	1241.07
K+	123.91	1.30	25.44	21.73	K+	72.30	3.89	17.46	22.89
Mg2+	318.08	5.15	142.97	86.78	Mg2+	776.14	13.72	195.08	262.19
Ca2+	210.12	2.56	88.74	51.06	Ca2+	912.72	14.22	236.70	320.59

Note: The unit of EC is mS/cm. SE: standard error.

). The water resources were all alkaline waters in Guangrao county. Yet, the average EC value in Kenli county was larger, and the TDS, as well. The concentrations of SO₄²⁻, NO₃⁻, and K⁺ in Guangrao county were all bigger than that in Kenli county, and the content of Na⁺ in the two areas was similar. The main ions in the water resources were Na⁺ and Cl⁻. The Ca²⁺ in Kenli county water resources was nearly three times higher than that in Guangrao county. The NO₃⁻ in Guangrao county was 10.05 mg/L, which was 10 times larger than in Kenli county, with an average value of 0.82 mg/L. The average SARs in the 2 investigation areas were 21.88 and 16.01 mmol/L, respectively, and the minimum value of the SARs were all lower than 5 mmol/L; this represents the existence of suitable water resources in the study areas.

3.1.3. Water Quality Assessment

The evaluation by farmland irrigation water quality standards (GB) showed that the irrigation water in Kenli county was utilizable (Figure 4). However, the quality of the other water resources in the two sampling areas were all low. The utilizable drainage in Kenli county accounted for about 60%; this represents the big potential to develop drainage reuse engineering in this area. The drainage in Guangrao county holds an unusable proportion of 90%, showing little value in use. The underground water had a higher proportion in the utilizable section.

The irrigation coefficient method possesses more classic details, making the evaluation results have more reference value (Figure 5). Most of the water samples in Guangrao county were unusable or not suitable for use. The irrigation water had a relatively higher quality in Guangrao county; compared to other water samples in this area, about 20% of the samples showed a useable criteria. The water samples in Kenli county showed extremely different characteristics. The irrigation water possessed a proportion of 50% with well-suitable assessment results. This may be related to the origin of irrigation water, which was mainly obtained from the Yellow River.

According to the United States NRCS assessment methods, there were no water samples that could be classified as 1 or 2 level (Figure 6). About 30% of the irrigation water samples could be used after infiltration. The quality of the underground water and drainage water in Gurnagrao county indicated that they were suitable for developing saline water irrigation agriculture in this area. The water samples were mostly distributed in the 3 and 4 levels, and the 3 level water samples made up 30%, 50%, and 30% of the underground water, irrigation water, and drainage water, respectively.

The SARs of irrigation water samples in Guangrao county were all higher than that in Kenli county (Figure 7). Some samples in Kenli county showed a very high SAR value of 44 mmol/L, which was absolutely bigger than the average value. Therefore, when using the drainage water resource, it should be clearly distinguished after the measurement. The average SAR value of drainage water in Guangrao county was higher than 20, so it could not be used in this area. The SAR of irrigation water in Kenli county changed between 8 and 15 mmol/L; they were safer water resources.

The evaluation of obligate ion toxicity showed that the water resources in Guangrao county and drainage water in Kenli county were unsuitable for agriculture, when judging by the Cl⁻ toxicity assessment method (

Table 8. Evaluation of obligate ion toxicity level.

		Guangrao County			Kenli County
		Underground Water	Irrigation Water	Drainage Water	Underground Water	Irrigation Water	Drainage Water
Na+ toxicity	Low	0%	20%	0%	33%	50%	67%
	Moderate	20%	40%	14%	33%	50%	0%
	High	40%	20%	43%	0%	0%	0%
	Very high	40%	20%	43%	34%	0%	33%
Cl− toxicity	Low	0%	10%	0%	0%	0%	0%
	Moderate	0%	20%	7%	33%	50%	0%
	High	0%	0%	0%	0%	0%	33%
	Very high	100%	70%	93%	67%	50%	67%

). According to the Na⁺ toxicity evaluation results, the water quality in Kenli county was relatively well. Water resources management in Guangrao county should be conducted when cultivating plants in this region. When planting crops in the Yellow River Delta, the Cl^--sensitive plants should be paid more attention to on their growth soil environment.

As listed in

Table 9. FAO Irrigation Water Quality Assessment.

		Guangrao County			Kenli County
		Underground Water	Irrigation Water	Drainage Water	Underground Water	Irrigation Water	Drainage Water
Degree of water availability on crop affected	Mild to moderate	40%	60%	7%	33%	100%	67%
	Severe	60%	40%	93%	67%	0%	33%
Degree of water infiltration affected	None	60%	60%	93%	67%	100%	33%
	Mild to moderate	20%	20%	7%	33%	0%	33%
	Severe	20%	20%	0%	0%	0%	34%

, the irrigation water resources all reached the irrigation criteria of the FAO standard. There was about 67% of the samples that could affect crop water availability in underground water in this region, and the drainage water samples that could slightly affect crop water availability occupied up to 60%. This indicated that the drainage water in Kenli was useful for irrigation. It made up about 60% of irrigation water, which belongs to the mild harmful degree. The useable proportion of underground water was 40%; it was higher than that of Kenli. Furthermore, the drainage water that could affect crop water availability occupied up to 93% in Guangrao county, so it will be a practicable way to grow salt-enduring plants and explore marginal water resources.

3.2. Unconventional Water Resources Utilization

Unconventional water resources (UWRs) can be an alternative water resource and thus overcome water shortage. The UWRs in this experiment represent the water samples that are not suitable for irrigation after evaluation by various assessing methods. The statistical results represented that the pH of UWRs in Guangrao county was higher than that of Kenli county, and the SAR value was similar at the same time. The ion density was too high in the UWRs samples, and they could combine with the Yellow River water to obtain the mixing water with certain criteria. The ratio of the Yellow River water to the UWRs changed from 2 to 20.5 in Kenli county and from 2 to 12.5 in Guangrao county. Guangrao county showed a better potential in developing UWRs.

4. Discussion

4.1. Coastal Region Water Resources Distribution and Water Quality Evaluation

The coastal regions are the concentration of the population, economy-developing areas; they are also rich in land resources [26]. The Yellow River Delta is the largest, most integrated, and youngest delta in China; it mainly formed surrounding the Yellow River, which has experienced agriculture expansion within the drainage basin [27]. The Yellow River water is the largest water source in the Yellow River Delta. However, the flow of the Yellow River varied yearly, affected by human activity, seasonal climate change, and extreme weather [28,29]. The precipitation could supply more useable water for agriculture (Figure 1), but it mainly concentrated during June to October. The extreme rainfall hindered the growth of the crop seedlings and influenced crop maturity [30]. If the rainfall could be retained without runoff, it would add limited water supplements for the Yellow River Delta development. Besides the river water and rainfall, the underground water resource was another huge water repository. Yet, the sea water intrusion affected the salinity of the underground water also. The underground saline water irrigation has developed for hundreds of years in the coastal area, as well as in arid lands [31]. Many measurements have been taken to adapt the saline environment for developing saline agriculture, such as biomaterial amendments [32], drip irrigation [33], nutrition regulation [34], planting salt-tolerant plants [35], and so on. These production methods need little water compared to the conventional planting. The nutrition regulation for soil salinity utilization was proved in our previous study [34], and it could enhance crop growth with no more water input. In addition, the drainage from irrigation or treated living water could also be reused as irrigation water for crop growth [36,37]. The drainage water reuse also needs more engineering and mechanical measures, thus increasing the input, and this should pay attention to avoiding secondary pollution and resource wasting [38]. Besides the terrestrial water resources, the sea water resource was another huge storage. The sea water utilization technology used in agriculture has been conducted in many reports, such as sea rice (Oryza maris) cultivation [39], sea farming [40], sea water desalination for irrigation [41], and so on.

Water quality in China is becoming a serious problem for agriculture and food safety [42]. Although it is difficult to provide a unified criterion for evaluating the agricultural water quality all over the world, the evaluating results are still comparable. The most important criteria for determining the suitability of irrigation water is its salinity ions hazards, for excess soluble salts directly affect growth and the physiological availability of water to crops. As determined in this study, the water samples in Kenli county had a lower pH and higher Mg²⁺ and Ca²⁺ concentrations, compared to Guangrao county. The waters were also alkaline as a whole (Table 7), the pH of the waters is controlled by the carboxylic acid content of the dissolved organic matter, poor diffusion rate of oxygen, and biological reduction of nitrate and sulphate. The Na⁺ was high compared to other ions in all the water resources in the study area; a high concentration of Na⁺ in irrigation water will result in a high soil ESP that in turn brings about the poor infiltration of water in soil, crust formation, low permeability, bad aeration, and low seedling emergence. Different evaluation methods have been designed for various purposes in practical production. The water quality was uniform in the Yellow River Delta after the assessment in this study; this is mainly affected by the location of the investigation area and its distance from the Yellow River and coastline [43]. Kenli county was near the Yellow River, and the river is overland, so it more attention should be paid to when the upstream runoff yield is added during the rainy season to avoid flooding [44]. In the saline soil environment, the water quality evaluation parameters primarily correlated to pH, SAR, EC, Na⁺, and Cl^-. The purpose of the evaluation methodology was to judge whether the water could be applied to agricultural irrigation, thus satisfying the growth need of the plants.

4.2. Water Resources Rational Utilization

It is estimated that by 2030, the global demands for water and food will increase by 40% and 35%, respectively [45]. In recent years, the continuous increase in population in China’s coastal regions has significantly increased the demand for water, and the conflicts among the utilization of agricultural water and other water consumption have become more acute [46]. Under future climate predictions, many coastal areas will be at risk, as the occurrence of coastal flooding is set to rise [47]. Therefore, rational utilization of the water resources can not only protect the ecology environment, but also avoid excessive consumption of natural and social resources. The Yellow River is a suspended river; the coastal agricultural lands surrounding the estuary will be affected by the drastic change of hydrological conditions. Furthermore, the Yellow River is also taking many sands from the upstream, decreasing its water quality and increasing the difficulty for using the Yellow River water. The river water, underground water, and drainage water comprise the most useable water resources in the Yellow River Delta. The irrigation water quality was the best among all water samples (Table 7), and the underground waters together supply the water as conventional water resources. The thresholds of salt tolerance of the main planting crops, maize and wheat, in the study area were 1.7 and 6.0 dS m⁻¹, respectively. Yet, the wheat needed more water during its whole growth stage, which was 790.8 mm, compared to the maize with 594.6 mm [48]. Except for the maize and wheat, some plants with economic value, such as sweet sorghum and saline-tolerant rice, were planted, and the planting area became broader and broader, and the flow of the Yellow River in the winter was lower than that in summer; thus, it needed a reasonable deployment of water resources during winter crop planting. Furthermore, the utilization of water should be according to the soil salinity, distribution of water resources, crop planting structure, water demand allocation, irrigation engineering, and so on. In addition, the industry and engineering development consumed much water and limited conventional water utilization [49]. Therefore, using the unconventional water resources is an important method to cope with the future challenges due to urban population growth and resource scarcity.

Unconventional water resources are considered as supplementary water resources that need specialized processes to be used as a water supplement [50]. In developing countries, using unconventional water for irrigation is a traditional and cost-effective method. However, its long-term development for agriculture will cause ecological and environmental questions [51]. In arid and semi-arid regions, salinization is common for an annual rainfall, which is unabundant to leach soil salts. Therefore, in these areas, there are little quantities of good-quality water, and this needs the use of saline water in agriculture. In the Yellow River Delta, the saline water resource is primarily an unconventional water resource. Although saline water can be used as an alternative of freshwater resources for agricultural irrigation, insufficient saline water quality and unreasonable irrigation technology may cause detrimental effects on plant growth, yield, and the quality of products [52]. The unconventional water could be combined with the Yellow River water for irrigation purpose, with the ratio between 1:2 and 1:20 (

Table 10. Water quality parameters of unconventional water sources and the Yellow River water.

Items	pH	EC (mS/cm)	SAR	Cl−	SO42−	Na+
Guangrao County
Minimum value	7.38	2.42	11.4	360.39	250.26	393.04
Average	8.33	6.85	23.51	1700.71	837.26	1192.41
Maximum value	8.95	15.97	38.26	4576.5	1259	2656.44
Kenli County
Minimum value	6.39	2.49	9.82	588.76	227.28	355.37
Average	6.93	11.36	21.98	3329.85	498.18	1602.74
Maximum value	7.97	24.49	44.3	7988.14	840.91	3370.18
The Yellow River water
Average	7.82	0.88	2.98	98.36	129.64	84.95

). This kind of utilization method has been processed in many countries, such as the USA, China, Australia, and so on [53]. Otherwise, we should pay attention to the specific ion salinity of the unconventional water, which affects crops by the high concentration of certain ions present in the irrigation water. The unconventional water will consume more Yellow River water, and this measurement should be taken in summer, when the flow of the Yellow River is largest. When using the drainage water for irrigation, we should pay more attention to the subsequent drainage water quality. The quality evaluation of the drainage water collected from unconventional water resources after irrigation utilization is necessary. For improving the efficiency of water resource utilization, more comprehensive solutions should be developed to increase the production of food resources and eco-environment protection in the Yellow River Delta.

5. Conclusions

Water resources are looked at as the lifeline of agriculture production, especially in the Yellow River Delta. The investigation in this study supplied supporting information on obtaining the water resources quality and utilization in this region. The quality of the irrigation water was best compared to the underground water resource and drainage water resource. The underground water and drainage water in Guangrao county were not suitable for irrigation. Kenli county was located near the Yellow River; it poses a good location advantage for irrigation and drainage water reuse. The unconventional water resource can be used through combination with the Yellow River water. Rational utilization of various water resources (irrigation water, groundwater, drainage water) is an important strategy for agriculture development in the Yellow River Delta.