Introduction

The world’s population is likely to expand by 10 billion by 2050, which would escalate the demand for food, fiber and fuel globally (United Nations 2021). This rising demand has led to a surge in water usage to improve productivity, despite the depletion of water resources worldwide at an unprecedented rate. The agriculture sector is the largest consumer of water using nearly 70% of available freshwater (The World Bank 2022). After rice and wheat, cotton has been most significant commercial fiber crop with considerable water demand and consumes nearly 11% of global irrigation water (West et al. 2014). Agricultural water scarcity is expected to affect 80% of the world's farmlands in next few decades (Liu et al. 2022) and thus demands for urgent measures to address it (Brar et al. 2012).

Cotton cultivation plays a vital role in supporting both industrial and agrarian economies. It serves as the primary raw material for the textile industry and provides employment opportunities for millions of people. Its cultivation employs about 7% of agrarian labor and provides income to 250 million people globally (World Wide Fund 2020). Currently, it is being cultivated in over 80 countries across the world, with India, China, United States of America (USA), Brazil, and Pakistan accounting for 75% of global production (Table 1). Water and nitrogen (N) are major production constraints in most of the cotton growing countries, as they are primarily located in arid and semi-arid regions. However, existing production tactics such as excessive fertilizer application and poor irrigation practices specifically in developing countries of Asia render cotton farming unsustainable from an environmental perspective. Cotton production in the world is 27 million tons and approximately 10,000 liters (L) of water is required to produce 1 kg of lint. This implies that a single cotton jean require about 4000 L of water, thus ranking requirement of cotton even higher than rice and wheat crops (Mekonnen and Hoekstra 2010, 2011). In fact, cotton cultivation over the globe is confined to water-constrained environments (Travis et al. 2020) and thus necessitates for rational use of available resources for sustainable cotton productivity through scientific interventions (Singh et al. 2021).

Table 1 Cotton statistics among major producer countries across the globe.
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Achieving water sustainability, while meeting future food and fiber demands is a major concern in modern crop production. Since, cotton is a major water-consuming crop, its poor management would lead to wastage of water and consequently its scarcity (Brar and Singh 2022). To address this issue, many cotton-growing countries have utilized drip irrigation and fertigation systems to overcome production limits imposed by poor water and fertilizer management. Novel methods of irrigation and fertilizer application through drip system (drip fertigation) aid in the efficient utilization of available water and nutrient resources, by putting them to rationalized usage for achieving higher profitability per unit of fertilizer and water applied (Solaimalai et al. 2005). Besides being cost-effective this system also provides precise water management as well as fertilizer application facility (Aujla et al. 2005).

Cotton is the world’s largest drip irrigated crop, accounting nearly 24% of its acreage under irrigation (Hossain et al. 2017). Drip system is continuously gaining popularity among farmers, owing to benefits such as potential savings in water and fertilizers besides better yield (Kang et al. 2012; Singh et al. 2018). Drip offers better advantages when designed, installed and managed correctly (Thompson et al. 2009). Apart from the numerous benefits, certain drawbacks hinder its large-scale adoption, namely high capital investment, damage during tillage operations and emitter clogging resulting in poor water distribution (Bralts et al. 1981; Capra and Scicolone 1998). Though, such issues can be addressed by providing incentives for purchase and installing the drip, proper chlorination and adjusting the emitter discharge (Yavuz et al. 2010; Shaw et al. 2018). Despite little limitations, we cannot oversee its benefits, which may improve the farmer’s economic status.

Materials and methods

To investigate the global progression of drip irrigation and fertigation in cotton and gain insights into its future perspectives for sustainable agriculture, we have constructed a meticulous database. The database encompassed various facets, including drip irrigation and fertigation practices, irrigation scheduling, economics, and future prospects from 5 major cotton-growing countries, viz. China, India, USA, Syria and Turkey. Furthermore, documented data of nearly 2 decades (i.e., from 2000 to 2022) from various scientific publications, thesis and dissertations submitted to various agricultural universities besides recently published reports and information provided from websites was also compiled. The information on drip irrigation studies conducted across the countries over the past 2 decades from Google scholar and other platforms such as J-gate plus, Cab direct, and Krishikosh has been accessed and used in presented study. The inclusion of keywords such as “drip irrigation”, “fertigation”, and “major cotton growing countries”, helped to search for the relevant literature across the platforms mentioned above.

In this investigation, a total of 124 studies involving research on cotton raised through drip conducted during last 20 years across the world were reviewed and presented in various tables and text. Out of this, 21 studies (2009–2022) from China have been reviewed, which primarily focused on reducing salinity effects through proper nitrogen scheduling with drip. Sixteen studies each reviewed for India and USA relate to management of nitrogen application through drip system. Unlike in India, where major focus is to conserve nitrogen fertilizer, the work in USA focused sub-surface drip irrigation with various sources of nitrogen and different scheduling approaches. Besides, 12 studies from Syria and Turkey have been discussed in lieu of the yield improvement in cotton under drip fertigation of nitrogen over surface application. Despite the abundance of available information, there remains a dearth of comprehensive and unified data on the evolution and development of drip irrigation and fertigation in cotton production over the past two decades. Consequently, this review article endeavors to provide a concise and informative update on the (i) current status of water and nutrient use in cotton, (ii) irrigation scheduling techniques and, (iii) drip irrigation and fertigation trends in cotton worldwide.

Drip irrigation history and development

The knowledge of drip irrigation dates back to 100 BCE, when unglazed clay pots buried in soil provided moisture to root zone in China (Bainbridge 2001). The first noticeable development has been reported in 1860, when German researchers installed clay pipes below the soil for sub-surface irrigation (Goyal and Megh 2012). A major breakthrough came several decades later in Australia, when Hannis Thill developed perforated plastic pipes, offering a more durable solution for irrigation. These perforated pipes allowed slow and precise water application, directly targeting the plant's root zone. Utilizing this advantage, Symcha Blass and Yeshayahu from Israel developed plastic emitter in 1959, which resulted in significant improvement of drip irrigation (Young 2017). This was followed by the invention of drip tape in early 1960's in the United States (Braud 1970), which is a long flat thinwalled tube, with regular perforations and was laid on soil for irrigation. Thus, drip irrigation has evolved over time, and sub-surface drip is now widely used for commercial cultivation. This innovation further revolutionized drip irrigation practices, enabling efficient water distribution and management.

The global water footprint and significance of drip irrigation in cotton

The global consumption of cotton fiber is projected to be 126 million bales in 2022–23 (Johnson et al 2022). The global water footprint (WF) of cotton products is estimated to be 233 billion m3 (BCM) year−1 (Mekonnen and Hoekstra 2010), which equates to 33 m3 year−1 per capita or 2238 bathtubs of water per person annually. Mekonnen and Hoekstra (2011) also reported that blue WF (surface and groundwater used for irrigation), green WF (rain or soil moisture consumed during the growing period), and grey WF (associated with nitrogen pollution) account for 33%, 54% and 13% of cotton’s total water use, respectively. Intensive agricultural practices to meet the needs of an expanding population have made agriculture a cause of water scarcity (FAO 2022). As water becomes increasingly scarce, mitigation strategies and conscientious use of water resources are critical concerns seeking urgent attention, and WF can be used as an indicator of agricultural water consumption (Hoekstra 2003).

The WF provides information on the total volume of freshwater used or polluted during the production cycle. Singh et al. (2022a) reported that cotton alone consumed 65–78% of total WF in a cotton-wheat cropping system in north India, while the remaining 22–35% has been attributed to wheat. It was further observed that under surface flood method, green, blue and grey components contributed 42, 48 and 10%, respectively, toward total WF for cotton. At the farm level, the adoption of practices that enhance input use efficiency can effectively reduce agricultural WF by improving water use efficiency (WUE) via crop diversification, conservation tillage (Azimzadeh 2012), increased water productivity (Chai et al. 2016), drip irrigation (Brar et al. 2022), and fertigation system (Singh et al. 2021). Therefore, better comprehension of surface and groundwater consumption as well as the implementation of the aforementioned techniques can aid in the achievement of sustainable water management.

The Xinjiang province, known for its welldeveloped drip fertigation system, plays a crucial role in China's elevated cotton production (Yuxin 2021). Many researchers have advocated for the adoption of drip irrigation and fertigation in areas experiencing over-exploitation of surface and groundwater for improved WUE and higher cotton productivity (Singh et al. 2018; Ma et al. 2021). For instance, Postel (1999) suggested that shifting cotton from surface to drip irrigation in India could lead to 25% higher yield, 60% reduction in water use, besides 169–255% increase in water productivity. Similarly, a report by CICR (2005) elucidated that when irrigated, cotton yield increased by 125.7% as compared to rainfed condition. Singh et al. (2022b) also highlighted that cotton crop consumed 32% lower water under sub-surface drip fertigation than surface flood, an indicator of remarkable water savings. In summary, cotton production has a substantial WF, and implementing sustainable water management practices such as drip irrigation and fertigation is crucial for enhancing WUE and increasing cotton productivity. Such approaches, when combined with other water-saving strategies, could contribute to the sustainable cotton cultivation and help mitigate the environmental impact of its production.

Irrigation scheduling and relevant scheduling techniques

Irrigation scheduling (IS) involves determining when, where, how much, and for what purpose irrigation water should be applied. Its primary objective is to maintain optimal soil moisture in the crop's root zone to support growth and development (Brar et al. 2019). As irrigation consumes a significant amount of water resources, prioritizing water conservation in the agricultural sector is crucial. Nevertheless, farmers tend to conserve water by employing conservational tillage (Afzalinia and Ziaee 2014), IS (Singh et al. 2018), mulching (Zong et al. 2021), and sub-surface drip fertigation technique (Singh et al. 2022b). Documented research suggests that IS is the most effective approach, as it perceives plant water needs, water availability, and soil storage capacity near the root zone (Gu et al. 2020).

Cotton, being a highly regulated crop requires precise water management at different phenological stages to maximize yield (Vellidis et al. 2009, 2011). Due to rising water demand and the ensuing scarcity of irrigation water for crop growth, researchers are globally collaborating on IS with drip technology to improve irrigation efficiency (De Jonge and Thorp 2017). A brief summary of drip irrigation practices being followed in cotton cultivation across the globe has been presented in Table 2.

Table 2 Summary of drip irrigation practices being followed in cotton cultivation across the globe
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To facilitate optimal irrigation scheduling, a range of tools, including sensors and computer models are available (Olalla et al. 1999; Tarjuelo and de Juan 1999). These tools rely on a variety of factors to estimate soil moisture and crop phenological changes during the growing season. The following sub-sections summarize key irrigation scheduling techniques based on these tools.

Scheduling based on evapo-transpiration

One widely used technique involves, assessing crop evapo-transpiration (ETc), to determine daily water use. The crop coefficient (Kc) is then used to develop irrigation recommendations using the equation ETc = ETo × Kc (Doorenbos and Pruitt 1977). ETo represents the reference crop evapotranspiration, calculated using the Penman–Monteith equation (Allen et al. 1998). The Kc values vary depending on the crop growth stage, ranging from 0.4–0.75 in the early stages, 1.15–1.20 in the mid-season, and 0.6–0.7 toward the end of the growth phase (Hunsaker and Elshikha 2017; Singh et al. 2018).

Sensor-based scheduling

Sensor-based scheduling involves using sensors to monitor soil moisture patterns, and utilizing the information for optimal irrigation scheduling. This method is particularly prevalent in developed countries. A natural resource assessment conducted by Cotton Incorporated revealed that nearly 10% of cotton growers use weather-based scheduling methods, along with soil and crop monitoring systems that incorporate sensors and wireless communication (Shah and Das 2012). Sensor-based scheduling relies on measurements of soil matric potential and canopy temperature.

There is long history about usage of sensors such as tensiometers (Hake et al. 1992), neutron probes in determining volumetric water content (Kamilov et al. 2003; Hunsaker et al. 2005), time domain reflectometry (Soler and Hoogenboom 2007) and gravimetric and volumetric water content (Khalilian et al. 2010), to monitor soil water potential for scheduling irrigation in cotton. Various types of sensor capable of measuring soil conductance and dielectric constant have been available for over two decades (Lieb and Fisher 2012). The presence of soil water in the pore spaces affects the soil's dielectric constant significantly. Granular Matrix Sensors (GMS) measures electrical resistance changes as soil water moves into and away from the sensor, providing an estimation of soil water tension (Hussain et al. 2020).

Canopy temperature based scheduling

Nowadays, canopy temperature is emerging as a valuable physiological trait for effective irrigation scheduling in cotton. Upchurch and Mahan (1988) reported that the normal canopy temperature for cotton is 27 ± 2 °C. Similarly, Wanjura et al. (1988) also observed that irrigating cotton, whenever the canopy temperature exceeded 29 °C or weekly soil moisture replacement in the root zone resulted in equivalent yields. Conaty et al. (2012) used a fluorescence assay to determine the ideal canopy temperature for cotton and found it to be 28–30 °C, and with deviations resulting in reduced production. Bronson et al. (2019) reported that N fertigation using reflectance-based canopy assessments could save 17–112 kg N ha−1without compromising yield.

Modeling for irrigation scheduling

Irrigation scheduling models offer substantial benefits for both individual farms and irrigation consulting services (Ortega et al. 2005). These models excel in simulating irrigation schedules under different levels of crop water stress and varying water availability constraints (Pereira et al. 1995). A few versions described below are well calibrated and have been successfully tested in cotton.

Baker et al. (1983) developed one of the earliest tested models (GOSSYM-COMAX), which provides daily guidance for administration of irrigation, nitrogen, and plant growth regulators to support cotton growth and development (Sequeira et al. 1998). Another widely employed model in cotton is ISAREG, which performs soil water balance calculations at the field level and simulates alternate irrigation schedules (Liu et al. 1998). This model is crucial in assessing the impact of water stress on yields (Cholpankulov et al. 2008).The Cotton 2 K model introduced by Thorp et al. (2014) for dry and semi-arid regions aids in understanding the interplay between plant-soil environment processes and field inputs (Attia et al. 2016). Aqua crop V 4.0 designed by Linker and Sylaios (2016), enables irrigation scheduling at various time intervals based on soil moisture depletion levels and allows for adjustments for water applied in cotton cultivation. These models contribute to decision-making in irrigation scheduling, leading to optimized water usage and improved crop productivity.

Drip fertigation

Fertigation in simpler terms refers to the practice of delivering fertilizers in liquid form via an irrigation system such as flood, sprinkler, or drip system. Since, here fertilizer is supplied in liquid form; its distribution and delivery are correlated with the wetting pattern. Supplying fertilizers in liquid form allows for their distribution and delivery to be correlated with the wetting pattern (Medina et al. 2007). By using drip irrigation with reduced water applications, cotton productivity as well as water and fertilizer use efficiency can be significantly improved (Singh et al. 2018). The fact that fertigation allows the application of a nutrient directly at the site of active roots as per crop requirement and scheduling fertigation (when, how, and how much to apply) offers the prospect of lowering nutrient loss associated with the conventional application (Zafari and Mohammadi 2019). Amid various irrigation systems, delivery through drip is most efficient as it expands the possibility of supplying optimal nutrients to the root zone with minimal loss besides reducing runoff, leaching, and enhancing cotton yield (Singh et al. 2022b).

One key advantage of drip fertigation is its minimal soil disturbance during fertilizer application, which helps prevent soil compaction. This innovative approach is being extensively used in Israel (Megersa and Abdulahi 2015) and the United States (Bronson et al. 2018). Drip fertigation system reduced fertilizer loss by cutting leaching and volatilization losses, while increasing the nutrient availability (Sinha et al. 2017). Studies have shown that fertigation, especially through surface or subsurface drip systems, outperforms traditional sprinkler methods in terms of fertilizer use and nutrient uptake in cotton (Hou et al. 2007). Drip fertigation can achieve nutrient use efficiencies as high as 90%, with leaching losses as low as 10%, compared to the conventional technique, which typically yields around 50% nutrient use efficiency (Prakash et al. 2019).Cotton growers who have adopted drip fertigation have reported significant benefits by savings of 20–30% fertilizer costs (Chen et al. 2010; Yadav and Chouhan 2016; Singh and Bhati 2018; Singh et al. 2018), along with water savings of 50–60% (Janat and Somi 2001; Aujla et al. 2005; Thind et al. 2012) compared to traditional irrigation methods (Surendran 2014). These findings highlight the practical advantages of incorporating drip fertigation into cotton farming practices, promoting resource efficiency and sustainable crop production.

Drip fertigation approaches in cotton: a global perspective of leading producers

Drip fertigation, has garnered significant attention among researchers worldwide due to its critical role in cotton production. Extensive studies have consistently demonstrated the substantial benefits associated with drip fertigation in enhancing cotton growth and maximizing yields (Ahmed et al. 2000). Comparisons between surface-irrigated cotton and drip fertigated cotton have revealed remarkable improvements, with seed cotton yield (SCY) increasing by over 50% in the latter case (Janat and Somi 2001). Moreover, Veeraputhiran et al. (2002) have highlighted the impressive water-saving potential of drip irrigation, reporting a 54.5% reduction in water consumption compared to furrow irrigation in cotton cultivation. The superiority of drip fertigation over traditional fertilization methods is elucidated by Gireesha's (2003) observations, where it resulted in higher yields and improved cotton quality.

A comprehensive analysis of the progression of drip fertigation practices in major cotton-producing countries has been diligently reviewed and presented in Tables 3, 4, 5, 6. These findings provide valuable insights into the advancements and adoption rates of drip fertigation techniques across different regions. By integrating precise water delivery, nutrient management, and efficient fertilization strategies, drip fertigation has revolutionized cotton cultivation, yielding remarkable outcomes in terms of productivity and sustainability.

China as a leading producer

Cotton production in Xinjiang, China, has a rich historical background and is currently the leading producer globally, contributing over 25% of the total output (Millward 2009). The implementation of micro-irrigation in China began in the mid-1970s, but it was not until the late 1990s, with the introduction of thin-walled drip lines that reduced the cost significantly (Li 2020). Cotton accounts for approximately 60% of drip systems being used in the arid region of Xinjiang. This was primary reason for the rapid adoption of drip irrigation in Xinjiang as it protected cotton from excessive evaporation and soil salinization in the root zone (Mohammad 2004). Drip irrigation combined with fertigation, plastic mulching, and high-density planting are some of the key cultivation strategies being practiced in this area to boost yield (Hou et al. 2009).

Numerous studies conducted in the past decade have aimed to determine optimal cotton irrigation and fertigation schedules (Table 3). Initially, the emphasis has been focused on improving yield by better understanding of the interactions between soil salinity and N fertigation, as adequate N management might help in mitigating the negative effects of salinity on crop growth. Several studies have indicated that increasing the amount of N applied as fertigation at the beginning of the irrigation cycle can mitigate the negative effects of salinity on crop growth, leading to improved yield and water use efficiency (Wang et al. 2018; Shareef et al. 2019). However, it was elucidated that excessive fertilization does not have a positive effect on salinity or nutrient use efficiency (Min et al. 2016).

Table 3 Trends of drip fertigation for cotton cultivation in China
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Studies by Zhang et al. (2012) suggest that applying normal N under moderate saline conditions and higher N in high-saline environments can enhance SCY and nitrogen use efficiency (NUE). Consequently, there has been a shift toward reducing N application rates and increasing use efficiency. Reduced N application or partial substitution of mineral fertilizer with bio-fertilizer and using enhanced efficiency nitrogen fertilizers like polymer-coated urea boosted the yield (Tao et al. 2017). However, these substituted fertilizers could not reduce N2O emission in cotton fields (Li et al. 2020b). On the other hand, urea fertigated in combination with nitrification inhibitors like nitrapyrin (Tao et al. 2018) and dicyandiamide (Ma et al. 2018) aided in minimizing N2O emission and improved NUE by efficiently conserving N fertilizer through drip fertigation (Liu et al. 2017).

Reduced N application via drip fertigation in high-density cotton planting (Luo et al. 2018), in light textured soils has increased the yield and NUE by 10 and 11%, respectively (Wang et al. 2018; Che et al. 2019; Li et al. 2020a). Consequently, China has developed an array of N management strategies, through drip fertigation to alleviate saline conditions and enhance productivity, establishing itself as one of the world's largest cotton producers (Chen et al. 2010; Min et al. 2016; Ma et al. 2021).

India as a major producer

Cotton plays a key role in sustaining the livelihoods of about six million farmers in India, with an additional 40–50 million people involved in its processing and trade related activities (Cotton Sector 2022). It also contributes to the country’s net foreign exchange through the export of raw cotton and its products, thus earning it the title of “White-gold.” India holds the title of being the world's largest producer of cotton, with a production of 362.18 lakh bales from a cultivation area of 120.69 lakh ha. Despite this advantage, the country faces challenges in terms of low productivity, with an average yield of only 510 kg ha−1 (Anonymous 2022). This low productivity is primarily attributed to rainfed cultivations, which occupies nearly 67% of total acreage (Cotton Sector 2022). Nevertheless, there has been a notable increase in the adoption of drip irrigation, which has led to an expansion of the irrigated area in the past decade.

Indian cotton is grown under a variety of environmental regimes and is primarily split into three agro-ecological zones: Northern zone (Punjab, Haryana, and Rajasthan states); Central zone (Gujarat, Maharashtra, and Madhya Pradesh states); and Southern zone (Andhra Pradesh, Tamil Nadu, and Karnataka states). The central zone accounts for the majority of the country's cotton production and frequently employ drip irrigation in its heavy textured soils. In contrast, cotton cultivation in the southern zone is predominantly rainfed (Gopalakrishnan et al. 2007). Research on the suitability of drip irrigation for cotton in the Northern zone commenced about a decade ago, with a primary focus on reducing system costs by modifying planting patterns to minimize lateral costs per unit area (Table 4). Studies by Aujla et al. (2005) and Thind et al. (2012) have shown that paired row sowing, as opposed to regular sowing, enhanced cotton yield and WUE, while reducing costs. Another study by Singh et al. (2018) suggested that drip fertigation with 75% recommended dose of N (RDN) at 0.8 crop evapotranspiration (ETc) holds promise for increasing SCY, WUE, and NUE in the Northern zone. However, the Indo-Gangetic plains, in the north zone, have more potential for drip irrigation since here the soils are light to medium textured and underground water is brackish (Thind et al. 2008).

Table 4 Trends of drip fertigation for cotton cultivation in India
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In the Central zone, research on drip irrigation primarily focuses on optimizing fertilizer dosage and fertigation schedules to maximize system benefits (Katkar et al. 2016). The key difference in irrigation practices between the Northern and Central zones lies in soil texture. The Northern zone's light textured soils require more frequent irrigations, while the heavy textured soils in the Central zone necessitate fewer irrigation splits. Additionally, the fertilizer dosage in the Central zone is generally higher compared to other regions (Pawar et al. 2014; Singh and Bhati 2018). The use of slow-release N fertilizers such as neem-coated urea and sulfur-coated urea is also gaining popularity in mitigating N losses, when applied through drip irrigation (Pawar et al. 2014). While drip irrigation and fertigation have gained prominence in the Central zone, their implementation in several southern states is still at the experimental stage, necessitating on-farm adoption to enhance productivity and income by harnessing the benefits through government support (Jayakumar et al. 2015; Yadav and Chouhan 2016).

The USA as the world’s top exporter

The USA, renowned as the world's top cotton exporter, holds a prominent position in the global market despite being the third largest cotton producer. With exports amounting to a staggering $7 billion, the US captures approximately 35% of the total global cotton export revenue (USDA-ERS 2021). More than 99% of the cotton grown in the US is upland, with the remainder being American Pima (The United States 1987; Travis et al. 2020).

Here, sub-surface drip irrigation (SSDI) has gained significant popularity over surface drip irrigation (SDI) due to its superior durability (Tollefson 1985). While SDI was initially introduced in the USA in 1959, its implementation was predominantly limited to high-value crops during the early stages. Challenges such as emitter clogging caused either by iron oxide or soil particles, as well as root intrusion, led to poor water distribution. These obstacles were successfully resolved through the introduction of chemical treatments to prevent clogging, the design of emitters with smaller orifices, and the implementation of effective irrigation management practices (Mitchell and Tilmon 1982). These advancements not only enhanced the longevity of SDI systems but also extended their suitability to annual crops (Camp et al. 2000).

The key cotton-producing states in the United States are Texas, California, Arizona, and Mississippi, with the major share coming from the southern high plains of Texas. This region is characterized by low and unpredictable rainfall, strong winds, and a short growing season besides scarcity of water and nitrogen in more than half of the area (Varvel et al. 1997). Consequently, Texas emerged as a pioneer in SSDI adoption during the early 1990s, and since then, its implementation has experienced remarkable growth (Hanson et al. 2000). To address these challenges, cotton production under SSDI remained focused on conserving water and nitrogen by scheduling irrigation at 75% ETc, which assisted in greater N recovery (Bronson et al. 2001). Phosphorus also plays a crucial role in SSDI, as its application as phosphoric acid promotes root system development, facilitating improved access to soil nutrients and enhancing fiber quality (Bronson et al. 2003).

Multiple studies conducted in the US highlighted the significance of applying N at the right time and in the correct amount to minimize losses due to leaching or denitrification, and prevent nutrient deficiencies throughout the growing season (Table 5). Here, N fertilization is not required during the first month of crop growth as maximum uptake occurs at full bloom and gradually declines thereafter (Boquet and Breitenbeck 2000). Advanced techniques, such as the canopy reflectance approach, which evaluated the normalized difference vegetative index (NDVI), have been employed by Yabaji et al. (2009) and Bronson et al. (2011) to determine the optimal stage of crop N demand. This in turn led to improved N management of cotton under SDI. Despite the adoption of water and N fertigation to meet the crop's requirements, the loss of N fertilizer as N2O due to nitrification remains a challenge in irrigated conditions in the US (Booker et al. 2007). Though, such issues can be addressed by using nitrification inhibitors such as Ammonium thiosulphate (ATS) and urease inhibitors, which can be applied with nitrogen fertilizers by drip irrigation (Bronson et al. 2018). Albeit majority of the global cotton growing area is in dry regions with limited water and rainfall, the US remains the leading exporter of cotton due to advancements in SDI and N fertigation (Bronson 2021).

Table 5 Trends of drip fertigation for cotton cultivation in US
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Turkey and Syria as prominent Middle-Eastern cotton exporters

Turkey and Syria are two important Middle Eastern countries making significant contribution to cotton industry (Johnson et al. 2021). Cotton cultivation in Turkey is primarily concentrated in 3 zones, the Aegean region, the Cukurova region (traditional cotton belt) and largest being Southeast Anatolia region. Since late 1980s, the Southeast Anatolia Project (SAP) has encouraged farmers to adopt drip irrigation and fertigation by providing government incentives (Uzen and Cetin 2016). As the textile demand continues to rise, Turkish farmers have responded by expanding cotton planting, leading to an increase in cotton price (Erdogan 2022). Notably, Turkey has emerged as one of the leading cotton exporters with generating revenue of $ 2.27 billion in 2021 (COMTRADE 2022).

Cotton is a strategic crop in Syria, with more than 20% of the population engaged in its production and processing. Syria accounts for about 7% of global cotton production, and derives a significant portion of its revenue from cotton exports, earning $ 369.04 million (COMTRADE 2022). Cotton is grown at private farms on 98% of Syria’s land as a summer crop and thus requires irrigation. In recognition of the importance of water conservation and yield improvement, the Syrian government has implemented measures to promote the adoption of drip irrigation for cotton cultivation, resulting in increased yields and improved water management practices (Westlake 2001). The goal of drip irrigation in both Middle Eastern countries is to conserve water and improve NUE (Table 6). Drip fertigation of 140 kg N ha−1 at 80% ETc and fixed partial root zone drying (irrigating both sides of plant row) boosted dry matter production, crop yield, and better water productivity (Mubarak and Janat 2018). Furthermore, optimizing N fertigation plays a vital role to reduce NO3− loss from the crop's effective root zone depth, resulting in significant water and nutrient savings (Janat and Somi 2001; Cetin et al. 2015).

Table 6 Trends of drip fertigation for cotton cultivation in Syria and Turkey
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Economics of fertigation

Drip irrigation has gained global recognition among farmers, although its widespread adoption has been hindered by the high initial costs involved. This irrigation method is particularly favored in regions facing severe water scarcity. In the realm of Indian cotton production, the cost of laterals and drippers alone accounts for 60–80% of the total cost of drip systems, with an estimated value of around ₹65,000–70000 ha−1 (Sankaranarayanan et al. 2011). Drip line alone constituted majority of initial SSDI cost, so instead of placing the laterals in every plant row, confining them to every alternate row (Camp 1998; Lamm and Trooien 2003) could reduce the cost by 30–40% (Henggeler 1995; Camp et al. 1997). Furthermore, the adoption of this strategy has been justified by the subsequent benefits it brings, including increased yield and fertilizer savings that can offset the initial investment.

Despite the high initial cost, numerous studies have substantiated the positive impact of drip fertigation on net returns and benefit-cost (B:C) ratio. Pawar et al. (2014) evaluated the benefits of drip fertigation over surface irrigation. The results revealed that drip fertigation @150:75:75 kg NPK ha−1 applied as water-soluble fertilizer (WSF) in 13 equal weekly splits from 10 to 100 DAS resulted in the highest net returns of ₹307,273 ha−1 with a B: C ratio of 2.96. Surface irrigation of same fertilizer quantity profited the least with a net return of ₹70,350 ha−1 and a low B: C (2.41). Several researchers have acclaimed that WSF had an additional benefit in fertigation over regular fertilizer (Shinde 2000). Placing drip laterals in alternate furrows at 0.3 m depth exercised positive effect on improving gross and net returns compared to all furrow irrigation (Enciso et al. 2005). Similarly, in Central India, Shruthi and Aladakatti (2017) envisaged that drip fertigation with 150 kg N and 75 kg K ha−1 in 6 equal splits at 15 days intervals resulted in higher gross returns (₹193,872 ha−1), net returns (₹134,262 ha−1), and B:C (3.25) compared to soil application. Singh et al. (2021) also observed that drip fertigation with 75 kg N ha−1elucidated financial advantage, with net returns of $ 1033.9 ha−1 over the conventional system ($ 885.6 ha−1) in North India. As water scarcity continues to increase, farmers are expected to shift their focus from flood to drip irrigation in cotton, which has demonstrated increased yield but could not impact gross margins statistically (Khor and Feike 2017).

Future perspectives and recommendations

Based on the comprehensive review presented in the preceding sections, it is evident that drip irrigation and fertigation hold the potential to boost the cotton output besides conserving 20–30% of fertilizer and up to 50–60% of water. However, the fact that the drip fertigation system is need of the hour has not yet received desired attention (Singh et al. 2022a). Proper irrigation scheduling, adjusting the drip system to meet the local agro-climatic needs through mulching, saline water usage, alternate placement of laterals, and N supply based on crop demand are among some important aspects which can greatly help farmers across the globe in improving cotton productivity and net returns in a sustainable manner. Moving forward, there are several key areas where future studies can contribute significantly to the field of drip irrigation and fertigation in cotton cultivation. Firstly, efforts should focus on promoting the adoption and awareness of drip irrigation and fertigation techniques among cotton farmers. This can be achieved through educational programs, addressing barriers to adoption, and providing training to enhance farmer’s understanding and skills in managing drip irrigation systems. Additionally, future research should explore precision management in cotton by, tailoring irrigation and fertilization strategies to different cotton varieties based on their specific requirements. This customization can optimize resource use and improve overall productivity (Singh et al. 2021).

Another important aspect for future studies is the management of water quality in drip irrigation and fertigation systems. Research should investigate the impact of poor water quality, such as salinity or contamination, on system performance and longevity. Developing strategies and technologies to mitigate these effects will be crucial for sustainable water management and maintaining the effectiveness of drip irrigation systems (Brar et al. 2022). Additionally, comprehensive economic analysis should be conducted to assess the financial viability of drip irrigation and fertigation. Cost–benefit assessments and comparative studies of different practices will provide valuable information on the economic implications and potential profitability of adopting these techniques in cotton farming. Lastly, supportive policy frameworks are essential for the widespread adoption of drip irrigation and fertigation. Future studies should emphasize the importance of policies that incentivize and facilitate the implementation of these water-saving technologies. Financial assistance, subsidies, and favorable regulations can encourage farmers to invest in drip irrigation and fertigation systems. Collaboration between researchers, policymakers, and industry stakeholders is crucial to ensure the successful implementation and scalability of these practices. By considering these future recommendations, the field of drip irrigation and fertigation in cotton cultivation can be further advanced, leading to enhanced productivity, resource efficiency, and sustainable agricultural practices. These recommendations provide a roadmap for future research and policy initiatives in the field, aiming to address the challenges and unlock the full potential of drip fertigation in cotton production.

Scope of drip fertigation in developing countries of Asia

When we look at the broader perspective, India remains the world’s largest producer of cotton, followed by China, USA, and Pakistan. Since its independence, India has made significant strides in cotton production. Government policies emphasizing cotton research, subsidies for quality seed, and fertilizers through subsidies and minimum support prices have propelled India to its current position as a global leader in cotton production, although productivity levels still remain low.

However, despite occupying 36% of the area and contributing 23% of global cotton production, the productivity (510 kg ha−1) significantly trials behind the global productivity of 808 kg ha−1 (COCPC 2022). Rising input costs, including wages, and the unsustainable practices of excessive water usage (through surface flood irrigation) and overreliance on fertilizers and pesticides, have become pressing concerns. In this regard, the widespread adoption of drip irrigation and fertigation in cotton farming emerges as a practical solution to address these challenges while enhancing yields and ensuring financial stability to marginal farmers. Extensive research conducted by various experts validates the effectiveness of drip irrigation in Indian cotton farming (Table 4). Currently around 40,845 ha of India’s cotton is under drip irrigation, yet there is considerable untapped potential to expand this water-efficient technique to approximately 6.28 lakh ha through command and irrigation projects (Bhaskar et al. 2005). Recognizing the importance of irrigation, the Indian government has launched the Prime Minister Krishi Sinchai Yojana (PMKSY), a comprehensive irrigation scheme aiming to provide irrigation to every field across the country. Notable, cotton-producing states such as Gujarat, Andhra Pradesh, Tamil Nadu, Maharashtra, and Karnataka have made significant strides in implementing this scheme (GOI 2017).

Despite the potential benefits of drip irrigation, the high installation costs have been a deterrent for many farmers (Brar et al. 2022). In response, the Union government has subsidized the inputs through the National Mission on Micro-Irrigation (GOI 2010), now integrated into PMKSY. Under this scheme, small and marginal beneficiary farmers installing micro-irrigation systems (drip and sprinkler) receive a subsidy of 55% of the total cost, while others receive 45%. The funding ratio between the Center and State governments is typically 60:40, except for the North Eastern and Himalayan states, where it is 90:10. The Union Territories receive 100% funding from the Central Government. At the moment, this scheme only covers 5 ha per beneficiary for the installation of a micro-irrigation system and could be successful in encouraging farmers across the country to adopt drip system. Since its launch in 2005–06, the area under micro-irrigation has increased 5 folds (i.e., 2.24 mha to 11.41 mha) until 2018–19. Currently, the scheme covers the installation of micro-irrigation systems up to 5 ha per beneficiary, and its success is evident from the five fold increase in the area under micro-irrigation, reaching 11.41 million ha, with drip systems accounting for 46.9% of the area (Chand et al. 2020). Command area development through drip irrigation, where water is conveyed to the field by canal or pipe system and applied through drip is the most efficient solution for water and energy saving. This could further help in bringing more area under irrigation (Jadhav 2019; Brar and Singh 2022). This can be achieved through systematic subsidies to cotton growers solely based on their financial status. Generally cost incurred on supplying irrigation water to crops is often ignored in Asian region while calculating the net returns and economics. To augment the potential of drip fertigation in Asia, it is critical to undertake supplementary measures such as strengthening the location specific research, providing comprehensive farmer training, as well as ensuring supportive policy frameworks. The integration of a canal network with drip irrigation could aid in the expansion of the irrigation area specifically in north-western India (Brar and Singh 2022). These endeavors will contribute to the broader goal of optimizing the scope and effectiveness of drip irrigation practices of the region.

Proposed application of drip irrigation and fertigation to other regions and policy implications

In addition to the major cotton-producing countries reviewed above, several other countries, including Brazil, Pakistan, Australia, Uzbekistan, Argentina, Egypt, and Greece are also prominent cotton producers (World Population Review 2023). The successful implementation of drip irrigation and fertigation in major cotton-growing regions such as China, India, the Middle East, and the USA provides valuable insights for promoting the adoption of these techniques in other parts of the world. China serves as an exemplary case for Asian countries facing similar water scarcity challenges, such as Pakistan and Uzbekistan, which are experiencing salinity issues and high water tables (Mikosch et al. 2020; Abduraupov et al. 2022; Yuxin 2023). Drawing from China's successful strategies, such as customized irrigation scheduling (Che et al. 2019) and tailored nutrient management (Wang et al. 2018) to mitigate salinity, these countries can develop their own approaches to implement drip irrigation and fertigation in their cotton farming systems. Likewise, the experiences of India, with its substantial adoption of drip irrigation in cotton cultivation, can serve as source of inspiration for countries like Australia and Argentina. Although these countries may have differing soil types, climates, and water availability, they face similar challenges, including market fluctuations (Qaim and de Janvry 2002; Pah 2014) and the impact of climate change (ICAC 2019; Condon and Claughton 2020), particularly in rainfed or dry land cotton production (Carballo 2013; Conaty et al. 2022). India's successful implementation of drip irrigation in dry land and rainfed regions, leading to water savings (Yadav and Chouhan 2016), can provide valuable lessons for these countries to overcome challenges and adopt sustainable water and fertilizer management practices in cotton production.

Considering Brazil's position as the second-largest exporter and its high cotton productivity, mainly under rainfed conditions (Anonymous 2022; Cotton Brazil 2022; USDA 2022), adopting drip systems can further enhance the resilience of cotton farming communities and increase cotton production (Solidaridad 2017). Furthermore, studies have shown that drip irrigation contributes to the reduction of cotton boll weevil mortality in Brazil (Faustino et al. 2021). The favorable agro-climatic conditions in Brazil combined with the advantages of drip irrigation can explore its potential to improve their productivity and export competitiveness. Egypt and Greece as significant cotton-producing countries in the Mediterranean can learn from the experiences of Turkey and Syria, which have successfully implemented drip fertigation to address issues of declining cotton area due to high cultivation costs, water scarcity, and low global cotton prices (Robinson 2009; The Syria Report 2011; ICAC 2021).

Nevertheless, the future perspectives and recommendations provided above facilitate widespread adoption of this research. While learning from the experiences of major cotton-growing regions and tailoring their techniques to suit the specific agro-climatic conditions and socioeconomic factors of each region, the other countries can unlock the potential of drip irrigation and fertigation to enhance sustainable cotton farming practices, achieve higher yields, and mitigate the environmental impact. Therefore, policy framers must advocate suitable alternatives having potential to reduce water footprint and support cotton growers to adopt economic water savvy technology rather than giving monetary aid to pump out underground water, which is non-replenish able in either part of the world. Considering the threat of dwindling water resources in upcoming future, utilizing drip fertigation system could support our environment by reducing total water footprint, while offering economically sustainable option to replace prevalent surface flood method of irrigation in most of developing countries.

Conclusion

With the alarming depletion of global water resources, the focus has now shifted toward revamping agriculture with those water savvy technologies, which could not only result in huge saving of irrigation water but also lead to better productivity. Thus, drip irrigation and fertigation have emerged as promising solutions for cotton cultivation, offering substantial water and input savings while increasing yields. Major cotton-producing countries such as India, China, the USA, Turkey, and Syria have made significant progress in adopting drip irrigation systems over the past decade. Despite the progress, challenges related to high installation costs and water quality management remains to hinder overall progress. To overcome these barriers, it is essential to promote awareness, provide farmer training, and implement supportive policies such as financial assistance and subsidies. The successful experiences of major cotton-producing countries serve as examples for other regions facing similar challenges. Lessons can be learned from their customized irrigation scheduling, optimizing nutrient management, and efforts in dry land and rainfed regions. These experiences can guide countries like Pakistan, Uzbekistan, Australia, Argentina, Egypt, and Greece to adopt drip irrigation and fertigation practices, enhancing their cotton productivity and mitigating environmental impact. The future lies in embracing drip irrigation and fertigation as sustainable water and fertilizer management practices in cotton cultivation, ensuring higher productivity, resource efficiency and longterm agricultural sustainability. With upcoming water scarcity, drip fertigation seems to be indispensable and may predominantly come forward for cotton cultivation among arid and saline regions for sustainable resource management. However, until policy makers incentivize such novel water savvy technology, while curtailing direct subsidy on power supply to pull out ground water, benefits are unlikely to be realized at ground level. Therefore, adopting drip fertigation through a proactive farmer friendly approach has an enormous potential to reduce total water footprint and would be certainly associated with novel dividends in near future.