The rice–wheat cropping system (RWCS) constitutes a dominant agricultural paradigm in Asia, particularly in southeastern Asia, encompassing an expanse of approximately 24 mha (Nawaz et al., 2019). It occupies approximately 13.5 mha across South Asia’s Indo-Gangetic Plains (Padre et al., 2016). This cropping system holds paramount importance for the maintenance of livelihoods, food security, employment, and income generation for millions across Asia. Approximately 33 and 42% of the total acreage devoted to these crops are rice and wheat, respectively. In addition, it contributes significantly, at 25 and 33%, to aggregate rice–wheat production (Gupta et al., 2024). In northwestern India, the RWCS prevails as the principal cropping system, encompassing an area of approximately 12 mha (Bhatt et al., 2016).

On average, paddy cultivation yields approximately 5–6 tons of straw per hectare. It is estimated that Southeast Asian countries collectively generate 150 million metric tons of rice residues annually (Singh et al., 2021). The window between paddy harvesting and subsequent sowing of wheat, following field cleansing or paddy straw management, is markedly short, typically spanning 2–3 weeks (Meena et al., 2020), compelling farmers to resort to paddy straw burning. Paddy residue is assimilated through tillage post-partial incorporation/removal, facilitating expedited field preparation before seeding operations for the succeeding crop in the sequence (DOACFW, 2019). However, the RWCS faces numerous secondary challenges, including declining groundwater tables, deteriorating soil health, and diminished total factor productivity. One prospective strategy involves in situ management of paddy straw, encompassing direct drilling of wheat under no-till circumstances utilizing zero-tillage (ZT) machinery or a happy seeder (retention of residues on the surface). In addition, the incorporation of paddy straw into the soil can be achieved through conventional tillage (CT) machinery, such as harrows and rotavators, or straw chopping followed by mixing into the soil. Tillage is an energy-intensive farm operation which contributes to ~30% of the total energy use in crop production (Yadav et al., 2018). Retaining paddy straw as mulch on the surface of soil preserves soil moisture, moderates thermal regimes, enriches soil nutrient content, suppresses weed growth, and augments soil health, thereby fostering improved crop yields. Nitrogen (N) dynamics may undergo alteration due to ZT and surface residue retention, thereby necessitating nuanced N management strategies vis-à-vis residue burning and conventional tillage (Singh et al., 2015). The influx of crop residue-derived N is intricately linked with soil N management (Zhang et al., 2021). However, ZT combined with residue retention holds promise for augmenting long-term N availability to crops by elevating soil nitrogen levels and the labile nitrogen pool within upper soil strata (Sun et al., 2015). The implementation of farming systems that conserves soil and water through minimal soil disturbances and residue retention cover is one of the best management practices and improving the fertility status and microscopic population in degraded lands (Babu et al., 2023). In the last 60 years, the consumption of nitrogen fertilizer in India has grown rapidly. Emerging trends have resulted in escalating losses of nitrogen, posing significant threats to the quality of air, soil, and freshwater resources and consequently jeopardizing climate, ecosystems, and human health (Móring et al., 2021). Conservation agriculture increases available soil water, saves irrigation water, reduces heat and drought stresses, reduces GHG emissions, captures carbon, and improves soil health in the long term (Dhillon and Sohu, 2024).

Crop residues serve as nutrient-rich sources, liberating essential plant nutrients upon microbial decomposition in the soil. Consequently, reintegrating crop residues into soil, instead of incinerating them, serves to enhance several soil quality parameters. To withstand soil health within the RWCS in northwestern India, it is imperative to manage rice residue in a manner that is economically viable, environmentally sustainable, and logistically feasible. Generally, crop residues comprise approximately 40 to 45% of the carbon content, the restitution of which to the soil facilitates its utilization by soil microbes, thereby bolstering the soil organic matter (OM) content and mitigating organic carbon (OC) loss (Bin et al., 2021). Soil organic carbon (SOC) plays a pivotal role in shaping biological soil properties (Varatharajan et al., 2022). Microbial populations exert a profound influence on nutrient accessibility and contribute to the growth of various soil health indices. Consequently, understanding soil biological attributes is highly important for sustainability (Harish et al., 2022; Gopinath et al., 2022). Parameters such as total microbial count (TMC), actinomycetes, diazotrophs, and enzymatic activities, including dehydrogenase, alkaline phosphatase, and urease, serve as pivotal indicators of soil eminence (Doran and Zeiss, 2000). Soil-inhabiting microbes are central to nutrient release and soil purification. The inherent characteristics of soil, encompassing various soil classes, exert control over the soil microbiota, which in turn plays a pivotal role in modulating soil nutrient contents and rendering them bioavailable (Majumdar et al., 2024). The decomposition and biochemical transformation processes are expedited by soil enzymes, facilitating the release of nutrients from plants (Meena et al., 2022). Soil bacteria play a pivotal role in converting OM from its organic to accessible inorganic form, thereby facilitating the breakdown of OM (Six et al., 2004). Soil microorganisms are sensitive to changes in soil moisture as it affects the physiological state of microorganisms and plants which may lead to changes in their population in the soil (Gangmei et al., 2024). Recycling crop residues is imperative for reintegrating organic matter into the soil (Rajanna et al., 2022). Reduced tillage practices coupled with stubble retention promote the proliferation of diazotrophs, which is ascribed to reduced soil composition, fostering an optimal soil pore network conducive to interactions between stubble decomposers and nitrogen-fixing organisms (Gupta et al., 2019; Li et al., 2021). In the short term, applying cereal residues may require higher levels of fertilizer N to account for N immobilization, compared to not using residues (Sharma et al., 2021). However, over the long term, returning crop residues can lead to a net build-up of readily mineralized soil organic N, potentially reducing crops’ fertilizer N requirements (Jat et al., 2019). The amount of N loss due to volatilization increases when the food–water pH and temperature are favorable (Hayashi et al., 2008). Broadcast application of PU results in higher food–water NH4 + -N compared to deep placement of N (Huda et al., 2016; Islam et al., 2016; Islam et al., 2018; Liu et al., 2015), which increases N loss through NH3 volatilization. Excessive use of N fertilizer through broadcast application has negative environmental consequences, including N₂O and NO emissions, nitrate pollution of groundwater, and eutrophication (Savant and Stangel, 1990).

The initial yellowing of upper wheat leaves observed under mulched conditions is associated with a reduction in soil temperature (minimum) during the late January period of 2020 and 2021, which is attributable to the insulating effect of mulch on the soil (Chaudhary et al., 2023). Consequently, a standard shift in agronomic practices concerning rice straw management is warranted to enhance resource utilization efficiency and system productivity. We hypothesized that combined application of N@150 kg/ha in 3 splits at basal, before, and after 1st irrigation and residue incorporation improve productivity of wheat. Hence, the present study aimed to explore the timing, number of splits, and nitrogen application rates of wheat crops to achieve improved productivity, microbial dynamics, and enzymatic activities and optimal nitrogen management in the northwestern Indian Plains. Given the circumstances within the RWCS, there is an urgent need for systematic research endeavors aimed at evaluating diverse nitrogen dosages and scheduling regimes to optimize productivity.

The impact of straw on crop yields is still under debate since field investigations across various pedoclimatic environments are indecisive, because of multiple and complex interaction of factors that affect the straw-derived N cycling under field conditions (Mu et al., 2016). Conservation tillage with residue retention (chopped and unchopped) significantly improved the physicochemical properties, microbial count, and soil enzymatic activities. Zero tillage with full residue (unchopped) in wheat exhibited a 5.23% increase in grain yield compared to conventional tillage with full residue (chopped), concurrently boosting the soil microbial count by 19.80–25%, the diazotrophic count by 29.43–31.6%, and the actinomycete count by 20.15–32.99% compared with conventional tillage.

Notably, there was a marked increase in SOC within the upper soil layer (0–15 cm) in ZTW-HS with full residue compared to that in CTW-DS (chopped) (Figure 4D). Numerous studies (Mondal et al., 2021; Zhang et al., 2021; Chen et al., 2021) have consistently reported significant increases in SOC under ZTW-HS compared to conventional practices. Throughout the study years, ZTW-HS and full residue load, both chopped and unchopped, exhibited higher soil moisture contents. Crop residues add a considerable amount of labile organic carbon to soils and boost enzyme activity due to the increased presence of microbial communities (Fang et al., 2018). Zero tillage (ZT) significantly enhances soil moisture availability by reducing soil compaction and ensuring a uniform distribution of soil micropores and macropores (Meena et al., 2015; Huang et al., 2012). Zero tillage with residue retention (ZTW) has become a vital practice for conserving soil organic carbon (SOC) and minimizing carbon mineralization. This practice boosts nutrient availability for crops, improves soil water-holding capacity, and promotes aeration through the formation of continuous soil pores in the root zone (Varatharajan et al., 2022; Biswakarma et al., 2022). In addition, retaining crop residues encourages a higher microbial population than residue removal in both ZT and conventional tillage (CT) systems (Govaerts et al., 2008). Over a 2-year crop cycle, ZTW-HS with full residue or stubble resulted in a significant increase in SOC within the upper 0–15 cm soil layer. This increase can be attributed to the disruption of soil macroaggregates under CT without residue, which promotes direct contact between straw and microorganisms, leading to increased carbon mineralization. In contrast, ZTW-HS with residue retention prevents direct microbial contact and provides fewer nutrients to microbes.

Soil microorganisms enhance soil quality, health, fertility, and overall microbial community. Among these parameters, microbial activity serves as a subtle indicator for assessing soil quality. Adding crop residues has been shown to stimulate the microbial activity of bacteria, fungi, and actinomycetes (Choudhary et al., 2018). Studies have demonstrated that rice straw returned to the soil, along with cow manure, significantly increases SOM, total N, and available P compared to those in scenarios without residue incorporation (Cheng et al., 2014; Gu et al., 2018; Moharana et al., 2012). Moreover, numerous reports have highlighted the positive impact of residue management, whether through incorporation or retention, on the soil organic carbon balance (Gangwar et al., 2006; Gupta et al., 2007). During the wheat season, rice straw returned to the soil promoted the growth and reproduction of soil microbes, which was conducive to the stability and promotion of microbial community structures. This accelerated the decomposition of straw and enhanced nutrient availability into the soil (Pathak et al., 2006; Tan et al., 2006; Qian et al., 2012). Straw incorporation enhances the metabolic activity of microorganisms, the relevant enzyme activity, and microbial population (Sharma et al., 2020a). The soil microbial population gradually increased up to 75 days after the sowing of wheat and decreased during later growth periods. Rice residue had a pronounced impact on the soil microbial community, particularly up to 75 DAS. However, at maturity, the increase in mineralization of the prevailing microbial community decreased, possibly due to the solubility of residues or relative microbial availability in the field (Lehmann and Kleber, 2015). The presence of an adequate amount of rice residue in the soil regulates soil temperature, facilitating better microbial reproduction up to 75 DAS and maturity. The TMC and diazotrophic count exceeded the actinomycete count under the various treatments, corroborating previous findings (Choudhary et al., 2018; Bhagat and Gosal, 2018; Stagnari et al., 2020). Microbial populations, including fungal, bacterial, and actinomycetes populations, were greater under ZT with surface residue retention than under ZT with incorporation or removal (Jat et al., 2019; Stagnari et al., 2020). These microbial communities likely have advanced to grow rapidly in response to easily mineralized OM (Whitman et al., 2016). Excessive nitrogen doses failed to enhance microbial quantity or enzyme activity. Studies suggest that high nitrogen levels can lead to the accretion of toxic substances, such as ammonia, which is detrimental to plant health and can impede the growth of certain microbial groups. In addition, excessive nitrogen can lower the soil pH, which is necessary for enzyme activity (Brzezińska and Włodarczyk, 2005).

Soil microbial activity and enzymatic activity are strongly linked to increased nutritional mineralization of native organic C after residue integration (Guenet et al., 2010; Kirkby et al., 2014; Liu et al., 2011). Enzymatic activity exhibits a strong relationship with the soil microbial population, with increased microbial populations correlating with enhanced enzymatic activities, such as DHA, APA, and urease activity. Residue management practices have demonstrated a considerable and favorable relationship between enzymatic activity and SMC during the study period. Similar findings were reported by Tang et al. (2020), who reported a positive correlation between diazotrophic and actinomycete counts and DHA and APA. These soil microbes are significantly improved under ZT conditions (Rajanna et al., 2022; Choudhary et al., 2018). ZTW-HS with full residue (unchopped) produced more grain, straw, and biological yields, similar to ZTW with partial residues (anchored stubbles). This finding aligns with previous research highlighting the significant effect of rice residues on wheat yield (Chandra, 2018; Dhar et al., 2014; Kesarwani et al., 2017; Sah et al., 2014; Singh et al., 2021; Pandiaraj et al., 2015). The higher wheat yield in straw-retained plots can be attributed to improved soil nutrient levels and microbial abundance following straw residue incorporation as mulch in the field (Chaudhary et al., 2023). ZT has emerged as the most competent tillage method for conserving resources and increasing wheat yield (Usman et al., 2013). Higher grain and straw yields of wheat were recorded with ZT-HS than with conventional methods (Nandan et al., 2018). The higher grain yield under the retention of residue/incorporation treatments can be ascribed to increased growth parameters, facilitated by improved SOM content, nutrient availability, and moderation of the soil’s hydrothermal regime (Gupta et al., 2016; Iqbal et al., 2017; Ram et al., 2013). Straw incorporation/retention enhances soil properties, leading to improved root growth, improved nutrient uptake, and ultimately enhanced plant growth and grain yield. Similar results have been reported by Gupta et al. (2016), Meena et al. (2015), and Sharma et al. (2019). The reason for the lowest yields under CTW when full residues are incorporated after a chopper and spreader could be that the N that bacteria utilize to break down incorporated residues causes the plants to turn yellow in the early days. T5 and T6 have lower yield due to more N losses as it was applied after 1st and 2nd irrigation.

Moreover, applying nitrogen in three splits (at sowing, before the 1st irrigation, and after the 1st irrigation) led to a 6.25% increase in grain yield than that in two splits (at sowing and after the 1st irrigation), significantly impacting wheat productivity in the soil. Optimal nitrogen management practices have been highlighted by Sidhu et al. (2007), who reported a greater grain yield of ZTW-HS in rice residues with fertilizer broadcasting at sowing and before the 1st irrigation. A study by Gill et al. (2019) determined that nitrogen management involving three equal splits applied at specific intervals was the most efficient practice for enhancing yield. Similarly, Singh et al. (2015) reported that specific nitrogen management practices significantly increased the mean wheat yield.

In summary, our study highlights the profound impact of various rice residue management techniques on the microbial characteristics of wheat, ultimately enhancing grain yield, SOC, and enzymatic activity. In particular, ZTW-HS (chopped) consistently demonstrated increased TMC and enzymatic activities, contrasting with the lowest count observed in CTW-DS (chopped), emphasizing the pivotal role of rice residue retention in fostering soil biological properties. Embracing zero tillage coupled with full residue retention, facilitated by machinery such as a happy seeder, has emerged as a crucial approach in rice–wheat cropping systems. This approach not only ensures the sustained productivity and income of farms but also enhances soil vigor and environmental quality. By adopting such innovations, the agricultural sector can improve rice residue management practices for long-term productivity and environmental sustainability, both regionally and globally. Moreover, optimizing nitrogenous fertilizer dosages for wheat crops alongside rice residue management approaches is imperative. Residue incorporation or retention significantly influences the chemical and biological properties of soil, reducing the need for nitrogenous fertilizers. In addition, our findings underscore the significant impact of nitrogen levels on wheat grain yield traits, with grain yield equivalent to the recommended N fertilizer dose (150 kg N/ha) with partial and full residue (unchopped) residue retention. Rice residue management in the rice–wheat cropping system is a multidisciplinary effort that combines technology advancements and sustainable agriculture techniques with economic considerations and legislative support. The agricultural sector may improve residue management techniques for long-term productivity and environmental stewardship by addressing these issues collectively in South Asia and globally in similar crop-growing regions. We must determine that the repercussions of harvesting crop residues for any purpose must be specified, and methods applied using site-specific technologies to ensure that productivity and agronomic resources are not jeopardized for future generations.