Abstract

Context

The rice-wheat cropping system in the Indo-Gangetic plains (IGP) of South Asia has been shown to have higher productivity. However, this benefit is offset by the unsustainable over-drafting of groundwater resources. Given the growing scarcity of water, it is imperative to investigate alternative crop establishment and irrigation methods that do not rely on the conventional puddled transplanting method (PTR).

Objective

This study aims to assess the impact of combining conservation agriculture-CA with sub-surface drip irrigation-SSD referred to as CA+, at different nitrogen (N) doses on physiological performance, crop yield, irrigation and nitrogen use-efficiency, as well as farm profitability of rice in the north-western IGP of India.

Method

A two-year field experiment was conducted to assess the effects of medium-term CA and the combination of CA with SSD (CA+) at three levels of N (0%, 75%, and 100% of the recommended dose), in comparison to PTR using recommended dose of nitrogen-RDN (120 kg N ha^-1). Indicators of crop growth (under CA, CA+), i.e., biomass, grain yield, water-use, water-use efficiency (WUE), nitrogen-use efficiency (NUE), and economic analysis of rice production were evaluated and compared with PTR.

Result

The results revealed that the PTR plots produced 15% and 11% higher grain yield than CA and CA+ systems, respectively, even at 100%RDN, due to a significantly higher number of fertile tillers. However, the application of 100%RDN and irrigation through SSD resulted in a significant increase in nitrogen uptake (4.5%) and remobilization (7.5%) into the grain compared to PTR. The CA+ plots demonstrated a reduction in irrigation water usage by 1.5 and 2 times compared to the CA and PTR systems, leading to a respective increase in WUE by 1.6% and 1.8%. PTR exhibited highest net returns, while the CA+ treatment– SSD-N100 achieved the highest benefit-cost ratio.

Conclusion

The combination of CA with SSD at 100%RDN offers significant benefits, including notable water saving, improved WUE, NUE and crop yield. This integrated approach presents a promising solution to address the pressing issues of food security and sustainability arising from water scarcity and groundwater depletion in South Asia.

Future implication

There is a need to increase awareness among farmers about the benefits of CA coupled with SSD i.e., CA+ , for water-intensive rice-based systems. Additionally, further research should focus on identifying ideal rice cultivars suitable for CA+ systems and determining the optimal specifications for drip lines and emitter discharge rates for diverse water-scarce agro-ecological conditions.

Introduction

Groundwater serves as an indispensable global water resource, playing a pivotal role in sustaining 40% of irrigation water and agricultural production on a worldwide scale (Siebert et al., 2010, Dalin et al., 2017). However, numerous agricultural regions are currently experiencing a rapid depletion of groundwater due to excessive extraction to meet the escalating water demand (Wada et al., 2010). This problem is further exacerbated by the adverse effects of climate change, urbanization, and population growth, which have significantly reduced water availability, particularly in South Asia (Jain et al., 2021). Notably, India stands out as the largest consumer of groundwater globally, where it accounts for 60% of the country’s total irrigation supply (Siebert et al., 2010, Dalin et al., 2017). High pumping rates have led to the depletion of groundwater aquifers, particularly in the northwest and south regions, facing critically low groundwater availability. Despite this critical situation, conventionally managed cropping systems with flood irrigation continue to dominate agricultural practices in India. Therefore, urgent attention must be given to the development of efficient and sustainable approaches that conserve water in water-intensive cropping systems like rice-wheat (RW), which are vital for ensuring food security (Yadvinder-Singh et al., 2014a).

The rice-wheat (RW) system, which covers a vast area of 13.5 Mha in India’s Indo-Gangetic Plains (IGP), with Northwest India accounting for half of it (Ladha et al., 2009), faces significant challenges in its conventionally managed rice production system, known as puddled transplanted rice (PTR). This conventional approach is not only labor and energy intensive but also demands substantial amounts of irrigation water, ranging from 1800 to 2400 mm per season. This conventional system also contributes to soil degradation, further jeopardizing its long-term sustainability (Chauhan et al., 2012, Jat et al., 2019). Moreover, the depletion of groundwater resources adds an additional risk to this traditional RW system (Choudhary et al., 2018, Kumar et al., 2018). In the past five decades, groundwater levels have consistently declined across majority of RW cultivation areas in India (Humphreys et al., 2010), with a five-fold acceleration in decline between 2000 and 2006 compared to the period from 1973 to 2001 (Yadvinder-Singh et al., 2014a). Given this alarming situation, urgent measures are necessary to ensure sustainable use of groundwater in the RW system.

Flood irrigation (FI), intensive dry- and wet tillage, and crop residue (CR) removal/burning are the primary causes of the inefficient water-use and deterioration of the soil and ecosystem health in PTR (Nayak et al., 2022, Parihar et al., 2022). To address these issues, CA-based practices such as zero-tillage (ZT), crop residue retention have emerged as a promising alternative to PTR, offering improved resource use-efficiency, crop productivity, farmer profitability, and soil quality (Choudhary et al., 2018, Ladha et al., 2009). CA-based ZT employing direct-seeded rice (DSR) and residue retention has demonstrated significant benefits, including regulation of soil temperature, reduction of evaporative water loss, improved soil infiltration and water storage, increased crop yield, and enhanced water use efficiency (WUE) (Jat et al., 2019; Yadvinder-Singh et al., 2014b). In the context of water conservation, several studies conducted in NW India suggested that crop diversification through CA-based maize-wheat rotation could be an alternative to conventional RW and/or CA-based RW rotation (Khedwal et al., 2023, Bhatt et al., 2021, Jat et al., 2020). Unfortunately, the preference for rice cultivation persists among farmers due to high market demand and assured procurement, limiting the adoption of maize crops (Jat et al., 2020, Jat et al., 2020).

To address the pressing issues of water scarcity in the irrigation systems of IGP, various alternative approaches have been proposed, such as reduced tillage, aerobic rice, direct-seeded rice, saturation irrigation, laser land levelling, alternate wetting and drying, stubble mulching. In recent times, micro-irrigation has emerged as a viable option for cultivating cereal crops such as maize (Jat et al., 2019, Rao et al., 2021), rice (Sharda et al., 2017, Sidhu et al., 2019), and wheat (Sandhu et al., 2019, Dhayal et al., 2023), offering benefits in terms of enhanced yield, improved resource efficiency, and profitability. Given this context, combining the CA-based practices with drip irrigation have potential to reduce water consumption while also gaining farmers’ acceptance as well. Therefore, employing a combination of CA practices and drip irrigation can be an effective solution to tackle the water scarcity challenges in the IGP. However, implementing surface drip irrigation in cereal crops is challenging due to the difficulties faced during field operations caused by the presence of laterals on the soil surface. To overcome this challenge and enhance the acceptance of drip irrigation in cereal-based systems, sub-surface drip (SSD) irrigation has been proposed as an alternative (Sidhu et al., 2019, Jat et al., 2019; Patra et al., 2021). SSD irrigation enables precise application of water and nutrients directly to the root zone, effectively limiting weed emergence and proliferation, reducing energy and labor costs, and complementing direct sowing under ZT practices (Parihar et al., 2022, Jat et al., 2021). Moreover, the implementation of SSD improves the efficiency of irrigation water usage in rice cultivation by minimizing water loss through evaporation and deep percolation (Rana et al., 2022) . Additionally, the practice of fertigation, which combines the application of nutrients with irrigation, reduces fertilizer losses caused by volatilization, runoff, and leaching, thereby improving fertilizer use efficiency (Sharda et al., 2017). Hence, combining CA-practices with SSD irrigation holds the potential to achieve economically viable yield even with a reduced application dose of nitrogen (N).

In the context of surface drip irrigation studies conducted in CA-based cereal systems, research on subsurface drip irrigation (SSD) is limited. Existing studies have primarily focused on yield attributes and water-saving potential, neglecting key physiological parameters such as water uptake efficiency, photosynthetic activity, nutrient uptake, and growth dynamics. A comprehensive understanding of the crop’s response in these conditions can be achieved by monitoring and evaluating these parameters. Photosynthesis and transpiration rates are influenced by climate, soil, and crop management factors. Combining conservation agriculture (CA) with SSD may alter the crop microclimate and create a favorable environment for growth and development. However, previous studies have shown variable effects of water-saving approaches in rice, as they can modify the soil’s physical and chemical properties compared to traditional practices (PTR), affecting nutrient availability, utilization, and crop establishment. By elucidating the physiological responses of rice plants to CA-based subsurface drip irrigation, we can gain valuable insights to optimize crop management strategies and improve overall productivity. Furthermore, this research can contribute to the development of more efficient irrigation systems and promote the adoption of sustainable farming practices.

While studies have examined the individual benefits of CA and SSD in terms of water and nitrogen savings, there is a lack of comprehensive research exploring the complementarity of these two technologies in impacting crop physiological responses, productivity, irrigation water use efficiency (IWUE), and nitrogen use efficiency (NUE) in CA-based rice-wheat (RW) rotations. Moreover, there is a scarcity of data on the physiological response, productivity, IWUE, and NUE of rice under CA-based RW rotation with SSD irrigation at different N rates. To address these knowledge gaps, we conducted a 2-year study in the NW-IGP of India. Our objectives were to assess the effects of combining CA practices with SSD irrigation (CA+) and CA with flood irrigation (FI) at different N doses, compared to the conventional practice of puddled transplanted rice (PTR), on rice’s physiological performance, yield, IWUE, NUE, and farm profitability. Our hypothesis is that combining CA with water and nutrient N application through SSD irrigation, even below the recommended N dose, can offer opportunities for water and N savings while maintaining productivity.

Section snippets

Experimental site and climate

The experimental field is located at the research farm of the Borlaug Institute for South Asia (BISA)-CIMMYT in Punjab, India (30.99°N, 75.44°E, 229 m above sea level). The medium-term trial began during the monsoon season of 2015 and involved combinations of tillage methods (PTR/CA), irrigation practices (FI/SSD), and residue management (removed/25% retained). Since 2015, the experimental site has been used for zero-tilled cultivation of wheat and rice with both FI and SSD irrigation, while

Leaf area index and Fractional intercepted photosynthetically active radiations

At the flowering stage (90 DAS), the peak values for both Leaf Area Index (LAI) and Fraction of Intercepted Photosynthetically Active Radiation (fIPAR) were observed, followed by a subsequent decline (Fig. 3 and Fig. 4). Among the different treatments, the PTR plots exhibited the highest LAI (4.41) and fIPAR (0.88), compared to CA+ and CA plots, even when subjected to 100% recommended dose of N (SSD-N100 and FI-N100). The application rate of nitrogen had a greater impact on LAI and fIPAR than

Effect of N and irrigation on plant growth parameters

The higher leaf area index (LAI) and fraction of intercepted photosynthetically active radiation (fIPAR) observed in the PTR plots compared to the CA and CA+ treatments can be attributed to better crop establishment, growth, and source strength, such as the number of tillers and leaf size (Seeraj et al., 2018, Singh et al., 2018). The PTR treatment achieved peak fIPAR during the flowering stage due to its high LAI, resulting in a higher photosynthetic rate (Yoshida, 1972) . Apart from PTR

Conclusions

Regardless of the irrigation system employed, rice exhibits high responsiveness to nitrogen (N) fertilization. Inadequate N application resulted in significant reduction in photosynthesis rate, plant growth parameters, biomass and grain yields, and yield attributes. While puddled transplanted rice (PTR) plots demonstrated higher grain yield compared to conservation Agriculture (CA) and CA+ systems, this productivity came at a substantial water expense. However, the integration of CA practices

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The first author sincerely acknowledges the support of the Indian Council Agricultural Research -IARI, for providing the scholarship and other facilities. The research was undertaken at CIMMYT-BISA Farm, Ludhiana, India, and was funded by the Indian Council of Agricultural Research (ICAR)-W3 grant to CIMMYT for Conservation Agriculture and CGIAR Research Programs on Wheat Agri-Food Systems through CIMMYT Academy. We also acknowledge all the support received from the Divisions of Agronomy, Plant