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Article

The Role of Collector-Drainage Water in Sustainable Irrigation for Agriculture in the Developing World: An Experimental Study

by
Jakhongirmirzo Mirzaqobulov
1,
Kedar Mehta
2,*,
Sana Ilyas
1 and
Abdulkhakim Salokhiddinov
1
1
Tashkent Institute of Irrigation and Agricultural Mechanization Engineers, National Research University, Kori Niyoziy str. 39, Tashkent 100000, Uzbekistan
2
Technische Hochschule Ingolstadt, Ingolstadt, Esplanade 10, 85049 Ingolstadt, Germany
*
Author to whom correspondence should be addressed.
World 2025, 6(1), 1; https://doi.org/10.3390/world6010001
Submission received: 22 November 2024 / Revised: 16 December 2024 / Accepted: 18 December 2024 / Published: 24 December 2024
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Abstract

:
This study investigates the feasibility of using mineralized collector-drainage water (CDW) for irrigating maize crops on light gray soils in the Syrdarya region of Uzbekistan, an area facing severe water scarcity and soil salinity challenges. The research is particularly novel as it explores maize production in marginalized soils, a subject previously unexamined in this context. The experiment was designed as a three-factor factorial study with three replications, following the guidelines of the Uzbekistan Cotton Scientific Research Institute. Five irrigation treatments (Fresh Water, Fresh Water 70% vs. CDW 30%, Complex Method (Mixing with Specific Rules), CDW 70% vs. Fresh Water 30% (Mixing) and only CDW) were evaluated using an Alternate Furrow Irrigation system, incorporating various mixtures of fresh water and CDW to determine their effects on soil salinity, crop health and yield. The amount of irrigation water required was determined using a soil moisture balance model, with soil samples collected at multiple depths (0–100 cm) to monitor changes in moisture content and salinity. Salinity levels and soil health parameters such as alkalinity, chloride, sulfate and cation/anion balances were measured at different stages of crop growth. Data were collected over three growing seasons (3 years). An analysis of the data revealed that using CDW, even in mixtures with fresh water, can sustain crop production while managing soil salinity. Notably, irrigation methods such as Mixing 70–30 and the Complex Mixing Method effectively reduced freshwater dependency and maintained the crop yield without significantly increasing salinity. The results suggest that CDW could be a viable alternative water source in regions where traditional water resources are limited. The findings have significant implications for improving water use efficiency and agricultural productivity in areas facing similar environmental challenges. This research not only contributes to the broader understanding of sustainable irrigation practices in arid regions but also provides a scientific basis for the wider adoption of CDW in Uzbekistan, potentially enhancing food security and supporting long-term agricultural sustainability in the region.

1. Introduction

1.1. Background and Context

Water scarcity is a critical challenge in many regions worldwide, particularly in areas with arid or semi-arid climates [1,2]. Central Asia is one such region, where the availability of fresh water is severely limited, and the challenges of water management are intensifying [3]. The region’s arid climate, coupled with increasing water demands driven by population growth and economic development, places significant pressure on its already strained water resources. As a result, addressing water scarcity is an urgent priority in Central Asia, vital for ensuring the sustainability of its agricultural sector and maintaining broader socio-economic stability [4,5].
Agriculture in Central Asia is a cornerstone of the region’s economy and food security. The sector is heavily dependent on irrigation, which accounts for a substantial portion of water use. This reliance on freshwater resources exacerbates the water crisis, as agriculture competes with other sectors for the limited water available [6]. The region’s historical reliance on extensive irrigation systems, often characterized by outdated and inefficient infrastructure, further complicates the water management challenge. Consequently, improving water productivity and adopting conservation practices in agriculture are crucial to mitigating the impacts of water scarcity in Central Asia.
Soil salinity can significantly impact crop growth by disrupting water uptake, nutrient absorption and overall plant health. High salinity levels in the soil create osmotic stress, making it more difficult for plants to absorb water, even when it is present in the soil. This leads to dehydration and reduced turgor pressure, affecting cell expansion and overall growth. Additionally, excessive salts can interfere with the uptake of essential nutrients such as potassium, calcium and magnesium, leading to nutrient imbalances and deficiencies. As a result, crops may exhibit stunted growth, reduced yield and poor quality. In severe cases, high soil salinity can lead to plant death, making it a critical factor in agricultural productivity, particularly in arid and semi-arid regions.
Recent efforts in agricultural water management in Central Asia have focused on enhancing water efficiency through innovative strategies, including the reuse of drainage water [7]. These interventions are essential for sustaining agricultural output while conserving limited water resources. Techniques such as precision irrigation, improved water delivery systems, and the reuse of collector-drainage water (CDW) are being explored and implemented to optimize water use in agriculture [8,9]. Such strategies are critical in Central Asia, where the competition for water between agriculture, industry, and domestic use is increasingly intense.
Water scarcity in Central Asia is a complex issue with wide-reaching implications for agriculture, society, the economy and the environment. The region’s water resources are not only limited but also unevenly distributed, leading to acute shortages in some areas, while others may have relatively more abundant supplies. The transboundary nature of many of Central Asia’s water bodies adds another layer of complexity, necessitating cooperation among countries in the region for effective water management [10].
Addressing water scarcity in Central Asia requires a comprehensive approach that integrates improved water management practices, technological innovation and regional cooperation. The reuse of CDW offers a promising strategy for alleviating water stress by providing an alternative source of irrigation water, particularly in areas where traditional water resources are insufficient to meet agricultural demands during critical growing seasons.

1.2. Special Focus on Uzbekistan and the State of the Art

Kyrgyzstan and Tajikistan are often referred to as the “water towers” of Central Asia due to their high-altitude, mountainous landscapes, which are the source of many of the region’s rivers. These rivers, fed by glaciers in these two countries, flow downstream to nations like Uzbekistan and Turkmenistan, where they are essential for irrigation. Approximately 90% of the electricity in Kyrgyzstan and Tajikistan is generated from hydropower, and both countries are continuing to construct new water reservoirs for hydroelectric power plants. However, these developments not only impact local biodiversity but also significantly alter the river flow to downstream countries [11].
Irrigation from the Amu Darya and Syr Darya rivers significantly impacts water flow, particularly as the majority of crops grown in Uzbekistan are highly water-intensive. Uzbekistan, as a key player in Central Asia, faces a particularly acute water scarcity problem, exacerbated by rapid population growth and the corresponding need for increased agricultural production [12,13]. Such water-intensive irrigation not only exacerbates water scarcity in Uzbekistan but also contributes to the degradation of the Aral Sea, a well-known global environmental crisis. Since 1950, the area of irrigated land in the Aral Sea basin has expanded from 3.5 million to 8.0–8.5 million hectares. This expansion, coupled with the development of previously unused land and the increased extraction of water from the region’s two main rivers, the Syr Darya and Amu Darya, for irrigation, has contributed to the drying up of the Aral Sea. Consequently, there has been a significant decline in both the quantity and quality of freshwater resources in the basin, disrupting the eco-hydrological balance of the region [14,15].
The intensification of agriculture, essential to meet rising food demands, is fundamentally constrained by the availability and quality of water resources. The deficit in irrigation water is compounded annually by declining water quality, posing significant challenges to agricultural productivity [16,17]. Figure 1 represents the administrative boundaries and key waterways of Uzbekistan.
Approximately 10% of Uzbekistan’s land is designated for irrigation, while agriculture consumes around 90% of the nation’s total water resources. However, rising water demand coupled with the impacts of climate change could significantly reduce the country’s water supply [18,19].
The scarcity of irrigation water during the critical growing season is a major barrier to fully exploiting Uzbekistan’s agronomic potential. The country’s climatic conditions are favorable for cultivating two successive crops on the same irrigated land within a single year [20]. However, this potential remains largely unrealized due to an insufficient water supply, particularly during peak demand periods. Existing water management strategies often fail to address the irrigation needs of secondary crops, leading to the underutilization of fertile land and the loss of valuable soil moisture through evaporation [21].
Soil salinity in Uzbekistan is increasing due to inefficient irrigation practices, such as over-irrigation and poor drainage, which cause salts to accumulate in the soil. The use of saline water for irrigation and traditional flood irrigation methods also contributes to this issue. The heavy reliance on water from the Amu Darya and Syr Darya for irrigation reduces river flows, increasing the concentration of salts in these waters. This not only degrades soil quality but also impacts the rivers’ ecosystems, further contributing to the environmental challenges in the region [22].
In Central Asia, widespread irrigation development began in the 1960s and 70s, focusing on transforming steppes and desert areas, particularly in the Amu Darya and Syr Darya river basins, to support cotton cultivation. The irrigation systems relied on outdated technologies, leading to rising groundwater levels and subsequent secondary soil salinization due to over-irrigation. This increase in salinized lands caused a decline in agricultural yields, with saline lands eventually covering 50% of the region’s arable territory [23]. Figure 2 represents the degree of salinity across the Uzbek region.
Addressing this challenge requires a multifaceted approach, as highlighted by various studies. One of the primary strategies suggested by researchers is the transition from traditional flood irrigation to more efficient methods such as drip and sprinkler irrigation [24]. These techniques have been shown to reduce water usage and prevent the over-application of water, which is a major contributor to rising groundwater levels and subsequent soil salinization [25]. Drip irrigation, in particular, delivers water directly to the root zone, minimizing water wastage and reducing the risk of salt accumulation on the soil surface [26].
The improvement of drainage systems is another critical component in managing soil salinity [27,28]. Studies have shown that inadequate drainage leads to waterlogging and the buildup of salts in the root zone, which diminishes soil fertility and crop productivity [29,30]. Upgrading and maintaining these systems can help to control groundwater levels and facilitate the removal of excess salts from the soil, thus mitigating the effects of salinization [31].
The introduction of salt-tolerant crop varieties is a complementary approach that has gained attention in the literature. Salt-tolerant crops can sustain productivity in saline environments, providing a practical solution for areas where soil salinity is difficult to reverse [32,33]. Research indicates that these crops can be particularly beneficial in regions where efforts to rehabilitate salinized lands are still in progress [34].
Effective water management practices are crucial in preventing further salinization. The literature emphasizes the need for precise irrigation scheduling and the use of advanced technologies, such as remote sensing, to monitor soil moisture levels [35,36]. These practices ensure that water is applied only when necessary and in amounts that do not exceed the soil’s capacity to absorb it, thereby reducing the potential for salinity buildup [37].
Rehabilitating salinized lands through techniques such as leaching and the application of soil amendments has been explored extensively. Leaching involves flushing the soil with large amounts of water to remove salts from the root zone, a practice that has shown promise in reducing soil salinity [38,39]. Additionally, the use of gypsum and other soil conditioners can improve the soil structure and enhance the leaching process, further aiding in the recovery of salinized lands [40,41]. The reuse of treated drainage water for irrigation is another strategy that has been investigated. Studies suggest that this approach not only conserves freshwater resources but also helps in managing the salt content in irrigation water, thus reducing the risk of soil salinization [42]. The controlled use of drainage water, particularly when blended with fresh water, can be an effective measure in regions facing severe water scarcity [21].
In response to these challenges, there is a pressing need to explore alternative, non-traditional sources of irrigation water. Collector-drainage water (CDW), a byproduct of irrigation practices on agricultural fields, represents one such underutilized resource. In regions like the Fergana Valley, an estimated 5.5 to 7.0 km3 of CDW is discharged annually into the Syrdarya River [43]. In the irrigated regions of the Republic of Uzbekistan, over 20–22 km3 of mineralized collector-drainage water (CDW), with concentrations of up to 3–4 g/L, are generated annually. Given the prevailing water scarcity, evaluating the potential for reusing CDW for irrigation and leaching is crucial for addressing water shortages.
Specifically, in the Syrdarya region, between 1.78 and 2.64 km3 of CDW is discharged through ten major collectors, including MMZ, Shuruzyak, GPK-42s, GPK-s, Sherbulaksay and others. This volume of CDW presents a significant opportunity for potential reuse in agricultural practices [43].
The increasing depletion of traditional water resources and the growing scarcity of irrigation water necessitate exploring alternative solutions, making the reuse of collector-drainage water (CDW) a viable strategy for improving water availability and enhancing agricultural productivity [44]. In Uzbekistan, year-round irrigation with CDW presents a strategic approach to mitigating the impacts of water scarcity on agriculture. By utilizing this often-wasted resource, continuous crop production can be sustained, optimizing agricultural output and supporting food security [45].
This research hypothesizes that year-round CDW irrigation can significantly enhance the productivity of irrigated lands by minimizing the reliance on conventional freshwater sources, which would be reserved primarily for the initial stages of crop development and for diluting saline CDW [46]. Such an approach aims to overcome water scarcity constraints and promote sustainable agricultural practices.
The study aims to evaluate the feasibility of using mineralized collector-drainage water (CDW) for irrigating maize crops on light grey irrigated soils in the Syrdarya region of Uzbekistan. Key objectives include developing an effective irrigation strategy for the 300 MB hybrid maize variety, assessing the impact of CDW on soil salinity and analyzing its effects on soil health and crop yield. This research is novel, as it explores maize production in marginalized soils—a topic not previously studied. The findings are anticipated to enhance water use efficiency and agricultural productivity in regions facing similar challenges related to water quality and soil salinity.

1.3. Novelty of the Research

The intensification of agriculture, essential to meet rising food demands, is fundamentally constrained by the availability and quality of water resources. However, there is very limited fresh water available compared to the growing needs, and the situation is further exacerbated by the decreasing availability of water. While marginal waters and CDW could be alternative sources, their utilization is often limited due to concerns about salinity. Therefore, finding ways to use these marginal waters for irrigation, particularly in a sustainable and economically viable manner, is critical. This study aims to address this specific aspect by exploring how marginal and drainage waters can be effectively used for irrigation, contributing to the broader goals of water sustainability, food security and climate impact mitigation, as outlined in the Sustainable Development Goals (SDGs). This research is crucial as it contributes to the synergy between SDGs, particularly those related to water, food and climate, by promoting sustainable and economically viable irrigation practices. By identifying and validating methods for utilizing marginal water resources, this study provides a pathway toward more sustainable agricultural practices that can meet the growing need for food production without further degrading critical water resources.

2. Materials and Methods

2.1. Methdology

The operational methodology for the study is illustrated in Figure 3. It starts with the Study Area and Experimental Design. The study was conducted in the Syrdarya region of Uzbekistan, an area characterized by light gray soils and facing severe water scarcity and soil salinity challenges. The experiment was designed as a three-factor factorial study with three replications, following the guidelines of the Uzbekistan Cotton Scientific Research Institute (UZPITI). The experimental site was chosen based on its representative conditions, including the presence of salinized soils and reliance on irrigation for crop production. The crop selected for this study was maize (Zea mays), known for its significant water requirements and high sensitivity to salinity, making it a suitable candidate for evaluating the effects of different irrigation water sources.
Under conditions of water scarcity in Uzbekistan, the demand for forage crops in agriculture has markedly increased. This rise is driven by population growth and improving household incomes, which have resulted in a greater demand for meat products, thereby necessitating the expansion of forage crop production. Furthermore, the limited availability of natural pastures in the country has intensified the need for supplementary forage crops to support the livestock sector. Maize has emerged as a critical crop in addressing this demand, with the “Uzbekistan 300” maize variety demonstrating exceptional success. Its superior adaptability to the local climate and soil conditions has significantly contributed to enhanced productivity and the sustainability of livestock farming. Thus, maize cultivation, particularly the adoption of the “Uzbekistan 300” variety, presents an optimal solution to the challenges posed by increasing forage crop requirements in water-scarce environments.
Five irrigation treatments were evaluated using an Alternate Furrow Irrigation (AFI) system. The AFI method was selected as it reduces water usage while maintaining adequate soil moisture for crop growth.
The irrigation treatments consisted of varying mixtures of fresh water and collector-drainage water (CDW), with mineralization levels ranging from 0.5 g/L to 3–4 g/L, in order to assess their effects on soil salinity, crop health and yield. These treatments were applied throughout the growing season to simulate different irrigation practices and determine the optimal blend for maintaining crop health and minimizing soil salinity. The amount of irrigation water required for each treatment was determined using a soil moisture balance model. This model integrated data from soil moisture measurements taken at different depths (0–100 cm) at regular intervals throughout the growing season. To monitor changes in moisture content and salinity, soil samples were collected at multiple depths and analyzed. The salinity levels were monitored at different crop growth stages (vegetative, flowering and maturity) to evaluate the impact of CDW irrigation on soil health over time. The experimental design employed a three-factor factorial analysis, considering the effects of the water source (fresh water vs. CDW), irrigation method (Alternate Furrow Irrigation) and salinity levels (low to high).
Data collected over three growing seasons (From 2021 to 2023, 3 years, and July to October) were subjected to statistical analysis using analysis of variance (ANOVA) to determine the significance of treatment effects on soil salinity, crop health and yield. Post hoc comparisons were made using the Tukey test to identify which treatments had the most significant impact on the observed parameters. The study also integrated the results of experimental data with existing models for water management. A specialized model was developed using the data collected from the experiment, incorporating factors such as groundwater table depth, soil properties and climatic variations. This model was used to simulate the long-term impact of CDW irrigation on the soil health and crop yield in the region. In addition to the technical aspects of irrigation efficiency and crop productivity, the sustainability of using CDW for irrigation was assessed. Factors such as the potential for long-term salinity accumulation, water use efficiency and the economic viability of CDW irrigation were evaluated. This assessment aimed to determine whether CDW could be a viable alternative to freshwater irrigation in the Syrdarya region, contributing to more sustainable agricultural practices.

2.2. Study Area

The experimental site for this study is located on the “Sobirjon-ota” farm in the Gulistan district of the Syrdarya region, positioned approximately at 40°50′21″ N latitude and 68°69′21″ E longitude (Figure 4). Situated in the southeastern part of the Mirzachul Steppe, the site is approximately 40 km southwest of the city of Gulistan. The total area of the experimental site is 1.0 hectares. Water for irrigation is sourced from the Kurgantepa branch of the Janubiy Mirzachul canal, delivered through an irrigation network composed of reinforced concrete trays. Land drainage is managed via horizontal drainage systems. The soil at the site consists primarily of light and sandy loam, typical of more than 65% of the irrigated areas in the Syrdarya region. This makes the site representative of the broader region’s soil and climatic conditions. The research focuses on evaluating the use of CDW for irrigating secondary crops, such as maize, under these prevailing conditions.

3. Development of a Novel Complex Mixing Method

In many countries situated within arid zones, the quality of irrigation water is commonly evaluated based on two primary criteria: the risk of soil salinization and the risk of soil alkalization. Globally, various methodologies have been developed for assessing and classifying irrigation water to ascertain its suitability based on these risks [47,48].
This classification has been widely adopted as a foundational framework for evaluating water quality in numerous countries. However, extensive research has demonstrated that regional variations in soil-reclamation practices, the climate and the quality of irrigation water necessitate the establishment of region-specific boundaries for irrigation water classes. Consequently, various countries, including Algeria, Israel, India, the Czech Republic and Russia, have developed customized irrigation water classifications [49,50]. These classifications consider factors such as water quality, soil texture and crop salt tolerance.
Researchers from various countries have conducted studies in the Central Asian steppe zones, achieving significant insights [21]. Specifically, Ibragimova and R.A. Alimova have proposed the use of groundwater with a mineral content up to 3–5 g/L for cotton irrigation in the Bukhara and Fergana regions [1]. A.U. Usmanov has further developed a methodology for assessing and classifying the suitability of collector drainage water for irrigation, categorizing water quality based on mineral content: “good” (0.2–1.0 g/L), “satisfactory” (up to 6.0 g/L) and “poor” (above 6.0 g/L) [21,51].
Despite substantial efforts by scientists across the globe, including those from the United States, Russia, Egypt and Pakistan, a universally accepted method for sustainable mineralized water use in irrigation remains challenging. This complexity arises from the need to consider multiple factors, as noted in the existing literature: water mineralization, chemical composition, regional climatic conditions, soil salinity, drainage infrastructure, groundwater depth, crop salt tolerance and other interconnected variables. Addressing these factors is critical in achieving effective and sustainable agricultural practices under constrained water resources.
Stepanov I.N. and Chembarisov E.I. [52] developed a complex mixing method that synthesizes various approaches through the following general equation, providing a framework for evaluating mixed water sources. In our study, based on a comprehensive literature review, we applied and further refined this method through experimental research conducted in the steppe regions of Uzbekistan (Equation (1)). This enabled us to parameterize critical factors, including groundwater table and quality, soil characteristics, crop tolerance and climate variability, ultimately advancing the methodology for practical applications in salinized environments.
Q i r r = Q c o l · M c a n − M m i x · Q c o l M m i x − M i r r
where:
  • Qirr = Irrigation discharge (m3/s)
  • Qcol = Collector Water Discharge as 100% (m3/s)
  • Mmix = Mixed mineralization—defined based on research results considering the soil composition and crop types
  • Mcan = Mineralization level of surface irrigation water from a canal defined before the irrigation period
  • Mirr = The mineralization coefficient, determined before the irrigation period in the irrigation canal, is from 0 to 1.
This approach allowed for the foundation of sustainable irrigation technology by mixing mineralized collector drainage water with fresh surface water, considering the soil, groundwater and plant species. Based on a comprehensive review of existing scientific literature, we utilized the equation above in our experimental study to optimize the mixing of fresh water with collector drainage water for irrigation. The experimental research, conducted in the steppe zone of Uzbekistan, demonstrated the applicability of this equation in determining the optimal proportions of the two water sources. By systematically accounting for the chemical composition and mineralization levels of both fresh water and collector drainage water, the equation enabled the development of tailored irrigation strategies. These strategies considered critical factors such as crop characteristics, crop characteristics, groundwater table depth and soil properties, ensuring sustainable and effective water management in salinized and water-scarce agricultural systems.

4. Results of the Experimental Study

4.1. Use of Drainage Water and Soil Salinity

The experiment was conducted as a three-factor factorial design, adhering to the guidelines provided by the Uzbekistan Cotton Scientific Research Institute (UZPITI), with three replications for precision. The study utilized a furrow irrigation system—specifically, Alternate Furrow Irrigation —and evaluated five distinct irrigation treatments:
  • Fresh Water (FW): 8 rows with 4 protective rows between them (spacing of 0.90 m) and a length of 30 m.
  • Fresh Water 70% vs. CDW 30% (Mixing): 8 rows with 4 protective rows between them (spacing of 0.90 m) and a length of 30 m.
  • Complex Method (Mixing with Specific Rules): 8 rows with 4 protective rows between them (spacing of 0.90 m) and a length of 30 m.
  • CDW 70% vs. Fresh Water 30% (Mixing): 8 rows with 4 protective rows between them (spacing of 0.90 m) and a length of 30 m.
  • Collector-Drainage Water (CDW): 8 rows with 4 protective rows between them (spacing of 0.90 m) and a length of 30 m.
The amount of irrigation water required to meet crop water needs was calculated using a soil moisture balance model. Soil samples were collected at two locations in four depth intervals (0–30 cm, 30–50 cm, 50–70 cm, 70–100 cm) following UZPITI methodology. Irrigation demand was assessed through soil moisture measurements with a pH meter/soil moisture meter (TPH01807). Soil salinity was evaluated three times (before irrigation, mid-season and end of the season), measuring parameters including alkalinity, chloride (Cl), sulfate (SO4), calcium (Ca), magnesium (Mg), anions, cations, total solids % and overall salinity levels. The quality of collector-drainage water (CDW) was monitored before each irrigation event, and groundwater levels were tracked throughout the experiment to assess their impact on irrigation effectiveness and soil conditions.
Soil moisture was measured using the ML3 ThetaKit sensor, and the moisture percentage was calculated through the gravimetric method. The results from the ML3 ThetaKit were validated against the gravimetric method, and both were found to be consistent. For soil pH measurement, soil samples were collected and mixed with water in a specific ratio to prepare a soil-water extract (slurry). The pH was then determined using the WTW ProfiLine Cond 3310 Conductivity Meter, which measures the electrical conductivity of the solution.
Figure 5 shows the measurement points and experimental design for the presented research.
Table 1 presents data on different irrigation strategies employed to optimize water use for maize crops, with a particular focus on the incorporation of drainage water as a substitute for fresh water. During the growing season of maize (from early July to October), four irrigation events were carried out in 2022. All irrigations were conducted according to the experimental scheme, where drainage and mixed waters were used for irrigation, while river water (sourced from an irrigation canal) served as the control. The study evaluated five distinct irrigation methods: pure fresh water (FW), varying mixing ratios of fresh and drainage water (Mixing 70–30, Complex Mixing Method, Mixing 30–70) and completely drainage water (CDW). The data were collected across five irrigation events, each with specific dates and consistent land area (0.2 hectares). The irrigation rate is detailed in terms of gross and net water usage per hectare (m3/ha), with the difference between these values (reset) indicating water losses or inefficiencies. Additionally, the use of drainage water is quantified both in absolute terms (m3/ha) and as a percentage of the total gross water supply.
In the FW method, fresh water was exclusively used, with a cumulative gross irrigation rate of 4663 m3/ha and a net usage of 3957 m3/ha, highlighting some inefficiencies with a reset value of 708 m3/ha. No drainage water was utilized, reflecting a complete reliance on fresh water. The Mixing 70–30 method introduced drainage water starting from the second irrigation event, with 30% of the water supply sourced from drainage. This method achieved a gross irrigation rate of 4682 m3/ha, with 1053 m3/ha of drainage water contributing 24% to the gross supply, thereby reducing freshwater dependency while maintaining similar net irrigation efficiency (4019 m3/ha). The Complex Mixing Method further increased the use of drainage water, with its percentage progressively rising across the irrigation events. This method achieved a gross irrigation rate of 4728 m3/ha, with 1891 m3/ha (43%) coming from drainage sources, suggesting a substantial reduction in freshwater use without compromising the net irrigation rate (4006 m3/ha). The Mixing 30–70 method, which reversed the ratios used in Mixing 70–30, relied on 70% drainage water, resulting in the highest gross irrigation rate (4840 m3/ha). The method demonstrated significant freshwater conservation, with 2567 m3/ha (56% of the gross supply) derived from drainage, while the net irrigation rate remained effective at 4144 m3/ha. At 67%, the mineralization level of collector-drainage water decreased to its minimum value during the June–October period, while at 34%, it reached its maximum level of mineralization. A similar trend is observed with the Complex Mixing Method.
Lastly, the CDW method used only drainage water, achieving the lowest gross irrigation rate (3951 m3/ha) and a net irrigation rate of 3358 m3/ha. In this method, 80% of the gross water supply (2777 m3/ha) was from drainage sources, illustrating the method’s efficiency in utilizing alternative water resources. The study demonstrates that integrating drainage water into irrigation practices for maize can substantially reduce freshwater consumption without significantly compromising irrigation efficiency. Methods such as Mixing 70–30 and the Complex Mixing Method offer a balanced approach, effectively conserving fresh water while maintaining adequate net irrigation levels. The CDW method, while promising in its ability to minimize freshwater use, may necessitate careful management to avoid potential negative impacts on crop health and yield due to the exclusive reliance on drainage water. These findings underscore the importance of optimizing water resources in agriculture to enhance sustainability and resilience, particularly in regions facing water scarcity. The adoption of these irrigation methods could be pivotal in achieving water conservation goals and ensuring the long-term viability of agricultural practices. Figure 6 provides an insight form the on-farm data collection.
The experiments also evaluated changes in groundwater levels to assess the sustainability of the irrigation methods. Throughout the crop growing period, an increase in groundwater levels was consistently observed across all irrigation variants, including those using fresh water, mixed water and completely drainage water (c.f. Figure 7).
This rise in groundwater levels indicates that the irrigation practices, irrespective of the water source, effectively contributed to recharging the groundwater table. The uniform increase across different water sources demonstrates that both fresh and drainage waters were capable of percolating through the soil profile, thereby enhancing groundwater storage. This finding is particularly significant as it underscores the potential of utilizing mixed and drainage waters not only for effective crop irrigation but also as a sustainable strategy for maintaining and enhancing groundwater reserves, which is critical for the long-term management of water resources in agricultural regions.
In Uzbekistan’s climatic conditions, particularly during this period, precipitation is very low, and the beneficial portion of the rainfall is minimal. Changes in groundwater levels are primarily influenced by the irrigation regimes of neighboring fields with different crop types, due to variations in irrigation methods and crop selection. However, since the experimental field covers only 1 hectare, the impact of these factors was relatively minor. Additionally, the groundwater level in our field rose to a maximum of 1–1.5 m, which did not significantly affect the overall conditions. Therefore, the impact of precipitation was not considered a major factor in this analysis.
It is important to note that the final irrigation of the neighboring cotton fields had an impact on the experimental area. After this irrigation, the cotton fields were defoliated and prepared for harvest. An important consideration is that my field, being only 1 hectare in size and located in close proximity to the neighboring fields, may have contributed to the observed changes.
The experiment also included an analysis of soil dynamics to assess the effectiveness of different water treatment methods by tracking the concentration of a specific contaminant (measured in mg/L) over three years (2021, 2022 and 2023). The treatments involved various combinations of fresh water and Contaminated Drain Water (CDW), as well as a novel complex mixing method. Figure 8 represents the salt amount in % soil based on the measurement data for three consecutive years.
In 2021, the contaminant levels at the beginning of the year were the lowest in Case 1 (1.313%) and highest in Case 5 (2.005%). The novel complex method (Case 3) exhibited a moderately high level (1.733%), indicating it was less effective than pure fresh water but better than other mixed approaches. By the end of 2021, contaminant levels increased across all cases, with Case 1 remaining the lowest (1.155%) and Case 5 being the highest (1.854%). Notably, Case 3 (1.552%) and Case 4 (1.292%) showed significant improvements compared to their initial values.
In 2022, the initial contaminant levels followed a similar pattern, with Case 1 having the lowest (1.041%) and Case 5 having the highest (1.648%) concentrations. The novel method (Case 3) showed an initial concentration of 1.555%, suggesting stable performance. By the end of the year, the contaminant levels increased, with Case 1 and Case 5 remaining the lowest (0.999%) and highest (1.577%), respectively. Case 3 showed a slight improvement (1.520%), but other mixed approaches (Cases 2 and 4) also performed reasonably well.
In 2023, the starting contaminant levels were generally higher than in previous years. Case 1 started at 1.285%, while Case 5 began at 2.039%. The novel method (Case 3) began at 1.773%, showing similar effectiveness as in previous years. By the end of 2023, the contaminant levels remained the highest in Case 5 (1.843%) and the lowest in Case 1 (1.148%). Case 3 maintained a relatively stable concentration (1.702%), demonstrating its consistent performance.
In 2022, Case 1 had the lowest concentration (1.041%), and Case 5 had the highest (1.648%). The primary reason for this difference is that the fourth plot is located near the drainage area. On the left side, there is an irrigation canal elevated above the land surface, while on the right side, a collector-drainage network exists. The fourth method is closer to the drainage network and is continuously flushed, which explains the slight variation in the mineralization level there. The higher mineralization level observed in the fifth plot is attributed to its irrigation with water that has a higher mineralization. As observed, by the end of the irrigation period (during the final watering), we used 51% of the water from the collector, as its mineralization level was relatively low. Additionally, the use of 30% clean water positively contributed to reducing the mineralization.
The findings indicate that while the novel complex mixing method offers a reliable intermediate solution, it cannot replace the efficacy of pure fresh water. However, it may serve as a viable alternative in scenarios where fresh water is scarce. The study suggests prioritizing fresh water use for optimal contaminant reduction, with mixed methods reserved for resource-limited settings. Further research could focus on refining the novel complex method to enhance its effectiveness in contamination control.

4.2. Yield Comparison Across Experimental Variants

Figure 9 represents the yield comparison across various experimental setups by varying the value of CDW. In 2021, FW achieved the highest yield of 9500 kg, followed by FW-70 CDW-30 at 9069 kg, the Complex Mixing method at 9013 kg, CDW 70 FW-30 at 8200 kg and CDW at 7360 kg. In 2022, the yields decreased across all variants, with FW at 9200 kg, FW-70 CDW-30 at 8824 kg, the Complex Mixing method at 8646 kg, CDW 70 FW-30 at 7120 kg and CDW at 7070 kg. In 2023, the declining trend continued, with FW yielding 9250 kg, FW-70 CDW-30 at 8724 kg, the Complex Mixing method at 8605 kg, CDW 70 FW-30 at 7120 kg and CDW at 7002 kg. Across all three years, FW consistently achieved the highest yields, demonstrating superior performance, while CDW produced the lowest yields, indicating its reduced productivity. The other three variants—FW-70 CDW-30, the Complex Mixing method and CDW 70 FW-30—show intermediate results, with minor fluctuations. Overall, the declining yield trends over time highlight potential environmental or crop management challenges, emphasizing the need for further analysis to mitigate yield reductions and improve sustainability.

5. Outlook and Limitation of the Study

The study demonstrated that incorporating collector-drainage water (CDW) into irrigation systems can significantly reduce reliance on fresh water while maintaining adequate irrigation efficiency. This is particularly critical for regions facing acute water scarcity, like the Syrdarya region in Uzbekistan. Irrigation methods such as Mixing 70–30 and the Complex Mixing Method emerged as effective strategies, achieving a balance between water conservation and crop productivity. These approaches reduced freshwater consumption by up to 43%, highlighting their potential for sustainable water management in agriculture. The analysis of groundwater dynamics revealed that all irrigation treatments contributed to groundwater recharge, regardless of the water source. This indicates that CDW and mixed methods allow for effective percolation through the soil profile, enhancing groundwater reserves. Such an outcome underscores the potential of these methods to complement traditional freshwater irrigation by simultaneously addressing surface water scarcity and groundwater sustainability. While the study provided valuable insights into managing soil salinity, it highlighted the challenges of using CDW exclusively. Although the CDW-only method showed promise in conserving fresh water, it posed a risk of increased salinity and reduced crop health. Conversely, the Complex Mixing Method effectively mitigated salinity buildup, offering a practical compromise between resource efficiency and environmental sustainability.
One limitation of the study was the exclusive focus on maize as the test crop, which may limit the generalizability of the findings to other crops with different water and salinity tolerance. Future studies should consider a broader range of crops to validate the applicability of these irrigation methods. Another limitation was the relatively short duration of the experiment (three years), which may not fully capture the long-term effects of CDW on soil salinity, crop health and groundwater sustainability. Extended monitoring would be necessary to assess the cumulative impacts and refine irrigation strategies accordingly. Finally, while the study addressed the technical and environmental aspects of CDW irrigation, it did not comprehensively evaluate the economic feasibility or farmer acceptability of these methods. Future research should integrate economic analysis and stakeholder perspectives to ensure the practical implementation of these sustainable practices.

6. Conclusions

This study explored the potential of using collector-drainage water (CDW) as an alternative irrigation source for maize cultivation in the water-scarce Syrdarya region of Uzbekistan. The findings highlight that integrating CDW into irrigation practices can significantly reduce freshwater dependency while maintaining effective irrigation efficiency. Methods such as Mixing 70–30 and the Complex Mixing Method demonstrated promising outcomes by balancing water conservation, crop productivity and soil health. The analysis of soil salinity dynamics and groundwater recharge revealed that mixed irrigation approaches not only sustained crop growth but also contributed to groundwater replenishment, enhancing the sustainability of water resources. However, an exclusive reliance on CDW posed challenges related to salinity buildup, emphasizing the need for careful management to mitigate potential adverse effects. While the results underscore the viability of CDW in improving water resource efficiency, the study also identified limitations, including crop-specific findings and the short experimental duration. These aspects call for long-term evaluations and broader crop trials to generalize the applicability of the methods. Overall, this study provides valuable insights into optimizing irrigation strategies in regions facing water scarcity. By integrating mixed water use approaches, agricultural systems can achieve greater sustainability, resilience and resource efficiency, paving the way for improved water management in arid environments. The future scope includes investigating the long-term effects of CDW on different crops and exploring innovative water treatment technologies to enhance CDW quality for agricultural use.

Author Contributions

Conceptualization, K.M., J.M., S.I. and A.S.; methodology, S.I. and A.S.; software, K.M., J.M. and S.I.; validation, J.M. and S.I.; formal analysis, J.M.; investigation, J.M. and S.I.; resources, K.M. and A.S.; data curation, J.M. and K.M.; writing—original draft preparation, J.M., K.M. and S.I.; writing—review and editing, K.M. and A.S.; visualization, K.M. and J.M.; supervision, S.I. and A.S.; project administration, A.S.; funding acquisition, A.S. All authors have read and agreed to the published version of the manuscript.

Funding

We are thankful to the SDGnexus Network (grant number 57526248) Project of the DAAD’s “Higher Education Excellence in Development Cooperation—exceed” program for providing the opportunity to work on this study.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Administrative boundaries of Uzbekistan (top) and main waterways of Uzbekistan (Bottom) from open-source data.
Figure 1. Administrative boundaries of Uzbekistan (top) and main waterways of Uzbekistan (Bottom) from open-source data.
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Figure 2. The degree of salinity by regions of the Republic of Uzbekistan based on [23].
Figure 2. The degree of salinity by regions of the Republic of Uzbekistan based on [23].
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Figure 3. Operational methodology of the presented study.
Figure 3. Operational methodology of the presented study.
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Figure 4. The location of the case study area.
Figure 4. The location of the case study area.
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Figure 5. Measurement Points and experimental design.
Figure 5. Measurement Points and experimental design.
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Figure 6. On-site data collection and experimental images.
Figure 6. On-site data collection and experimental images.
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Figure 7. Change in groundwater dynamics with various cases.
Figure 7. Change in groundwater dynamics with various cases.
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Figure 8. Salt amount in % in soil based on the measurement data.
Figure 8. Salt amount in % in soil based on the measurement data.
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Figure 9. Yield Comparison Across Experimental Variants for 3 consecutive years.
Figure 9. Yield Comparison Across Experimental Variants for 3 consecutive years.
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Table 1. Results about the use of drainage water and the irrigation rate are shown where red represents the highest number and green represents the lowest number.
Table 1. Results about the use of drainage water and the irrigation rate are shown where red represents the highest number and green represents the lowest number.
202120222023
Irrigation Rate m3/haDrainage Water Use Irrigation Rate m3/haDrainage Water Use Irrigation Rate m3/haDrainage Water Use
GrossNetResetm3/haGrossNetResetm3/haGrossNetResetm3/ha
Only fresh water8727021700117399617807415641700
10188391790918777141010108401700
894724170089475713809047341700
951781170088375113208957331620
Fresh Water 70% vs. CDW 30% (Mixing)8727021700117399617807415641700
10188391793059187861322751010840170303
894724170268894763131268904734170271
951781170285886765121266895733162269
Novel complex mixing method8727021700117399617807415641700
10188391794489307901395211010840170283
894724170340906768138308904734170298
951781170485894754141510895733162403
CDW 70% vs. Fresh Water 30% (Mixing):8727021700117399617807415641700
10188391797139518211306661010840170707
894724170626922777145645904734170633
951781170666918783135643895733162627
Only CDW8727021700117399617807415641700
1018839179101894280413894210108401701010
894724170894918780138918904734170904
951781170951918779139918895733162895
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Mirzaqobulov, J.; Mehta, K.; Ilyas, S.; Salokhiddinov, A. The Role of Collector-Drainage Water in Sustainable Irrigation for Agriculture in the Developing World: An Experimental Study. World 2025, 6, 1. https://doi.org/10.3390/world6010001

AMA Style

Mirzaqobulov J, Mehta K, Ilyas S, Salokhiddinov A. The Role of Collector-Drainage Water in Sustainable Irrigation for Agriculture in the Developing World: An Experimental Study. World. 2025; 6(1):1. https://doi.org/10.3390/world6010001

Chicago/Turabian Style

Mirzaqobulov, Jakhongirmirzo, Kedar Mehta, Sana Ilyas, and Abdulkhakim Salokhiddinov. 2025. "The Role of Collector-Drainage Water in Sustainable Irrigation for Agriculture in the Developing World: An Experimental Study" World 6, no. 1: 1. https://doi.org/10.3390/world6010001

APA Style

Mirzaqobulov, J., Mehta, K., Ilyas, S., & Salokhiddinov, A. (2025). The Role of Collector-Drainage Water in Sustainable Irrigation for Agriculture in the Developing World: An Experimental Study. World, 6(1), 1. https://doi.org/10.3390/world6010001

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