The field experiment was carried out during the spring seasons of 2016–17 to 2018–19 at Sugarcane Research Institute (SRI) farm in Pusa, Bihar, India, with precise coordinates of 85° 40′ E longitude, 25° 59′ N latitude, and 52.1 m above mean sea level. This study was carried out as part of the Project Directorate of ICAR. The study area has a subtropical, hot and humid environment with a mean annual rainfall of 1,210 mm (Supplementary Table 1). Between July and September, 75–80% of the rain occurs. There were significant patterns of rainfall variability during the 3 years of the experiment, both in terms of amount and distribution, raising concerns about the reliability of the EIGP rainfall data. As illustrated in Figure 1, the mean maximum and minimum temperatures, relative humidity, and rainfall during the harvest period are presented. The total rainfall was 1,015.6 mm (2016–17), 1,134.6 mm (2017–18), and 871 mm (2018–19). During the growing year 2016–17, the mean weekly maximum and minimum temperatures ranged from 18.9 to 40.6°C and 6.2 to 27.2°C, respectively. Accordingly, in the year 2018–19, maximum and minimum relative humidity ranged from 75 to 92 and 48 to 82%, respectively.

The experiment was laid out in strip plot design with combinations of four planting methods and three irrigation schedules with three replications. In Table 1, detailed treatment combinations are presented.

Prior to cultivation, the experimental site was cleared, plowed, and harrowed manually. The gross plot size was 10 m × 9 m (90 m²) and the net plot size was 8 × 6 m (48 m²). Sugarcane variety “CoP 112” was planted on 10, 8, and 5 March during 2016, 2017, and 2018, respectively, using 150,000 buds ha⁻¹. Before planting, the cane setts were treated with chlorpyriphos 20% EC to protect them from insect attack. To supply 150:37.1: 49.8 kg N, P, and K ha⁻¹, diammonium phosphate (DAP), urea, and muriate of potash (MOP) were used. To provide a basal dose, half N and full P and K were applied. Sugarcane was top-dressed with remaining N doses in equal splits after the first irrigation and at the maximum tillering stage. In accordance with the treatments, sugarcane trash of 6 t ha⁻¹ was applied 50 days after planting. Based on a meteorological approach, irrigation water was scheduled based on a ratio between IW and CPE. To ensure good germination of sugarcane, sufficient moisture conditions were required, and irrigation was applied according to designated irrigation schedules based on a meteorological approach. As a constant depth of irrigation water (75 mm), irrigation was applied to achieve a pre-calculated CPE based on daily evaporation from a USWB Class A open pan. Each plot was irrigated with water measured by water meters. To prevent water from flowing from one plot to another, all plots were separated by double bunds. A conventional flat (CF) planted crop was irrigated throughout, whereas a paired row trench (PT) planted crop was irrigated only in trenches, resulting in a 40% reduction in the wettable area, which is 30 cm (trench) + 30 cm (15 cm + 15 cm both sides of the trench) out of 150 cm of 30:120 cm. To determine the amount of irrigation water applied over the growth season, the depth of water delivered to each treatment plot was multiplied by the total number of irrigations throughout the season. By using the gravimetric method, the moisture content of the soil was determined. The pooled mean of 3 years of number of irrigation, depth, effective rainfall, soil moisture contribution, and water requirement were given in Table 2. Before crop harvesting, irrigation was stopped 20 days in advance.

Water use efficiency (WUE) was estimated as follows (Tayade et al., 2020):

Water productivity is calculated as follows (Das et al., 2018):

In accordance with recommended practices, other agronomic practices viz., weeding, herbicide application and earthing up were followed as required. Sugarcane was harvested on 31st January of 2017, 2018, and 2019, respectively.

During a 3-year study, biometric observations of the cane growth and yield parameters were recorded, including germination percentage, number of tillers, plant height, millable stalk, single cane weight, and cane yield. In each 8 m long plot, the middle four rows were counted 45 days after planting (DAP) to determine the germination percentage. During 120 DAP, tillers were counted similarly for each plot and presented per hectare. The distance from ground level to the last fully expanded leaf was measured on 10 randomly selected plants from each plot at 240 DAP. Then, their average was calculated for the estimation of plant height.

At harvest, yield contributing characters and yield characteristics were observed. To avoid border effects, cane yield was harvested manually from net plots. For each plot, the cane yield was measured after topping the plants and removing the trash from the stems. In net plots, the number of millable stalks was manually counted and converted to thousands per hectare. During harvesting, 10 randomly stripped canes were collected for measuring cane diameter. By using a vernier caliper, the top, middle, and base of the cane were measured and averaged. From each plot, 10 randomly selected canes were weighed separately, and their respective values were presented as single cane weights. To extract cane juice, 10 randomly selected clean millable canes were crushed in an electric roller cane crusher. According to standard procedures (Meade and Chen, 1977), sucrose % was calculated.

In this experiment, the soil of the experimental site was sandy loam (Typic Haplustept). Initially, soil samples were pooled together, and a representative homogeneous sample was drawn and analyzed. At the beginning of the experiment (2016), detailed soil characteristics were determined, and the data are presented in Table 3.

After the harvesting of sugarcane in 2019, samples were taken from the cultivated soil layer at depths of 0–15 cm and collected with a screw sampler from each experimental plot. After drying, powdering, and sieving soil samples through a 2 mm plastic sieve, cloth bags were used to store the soil samples. We analyzed these processed soil samples for the parameters listed in Table 4.

Soil organic carbon stock (Mg ha⁻¹) in 0–15 cm depth = SOC (g kg⁻¹) × 2.22 × BD (Mg m⁻³).

An analysis of the data from the experiment was performed for each of the 3 years and then pooled together. Statistical Package for Social Sciences (SPSS v. 23.0) software was used for the analysis of variance (ANOVA). F-tests at a 5% significance level were used to determine the significance of the treatment effect. Using the critical difference (CD) approach, differences between treatment means were assessed (Gomez and Gomez, 1984).

Germination percentage and growth attributes are presented in Table 5. The results represent the pooled mean data of the crop of 3 years. Among the planting methods, PT planting (30: 120 cm row spacing) without trash mulching (PM₄) showed a significantly (p ≤ 0.05) higher germination percentage (37.6%) as compared to CF planting (75 cm row spacing) without mulching (PM₂; 33.3%) and was on par with rest of the planting method and trash management practices at 45 DAP. With regard to irrigation scheduling, IW/CPE ratio of 1.00 (IS₃) had the highest germination percentage (36.7%) accounting for an increase of 6.4% when compared to the IW/CPE of 0.6 (IS₁).

At 120 DAP, PT planting with trash mulching (6 t ha⁻¹; PM₃) produced the highest number of tillers (208,300 ha⁻¹) and was statistically significant (p ≤ 0.05) over other treatments. CF planting with (PM₁) or without (PM₂) trash mulching resulted in minimum tillers, accounting for 21.1 and 34.6% reduction respectively as compared to the treatment PM₃ (Table 5). Among irrigation schedules, IS₃ treatment recorded the maximum tiller number (215,500 ha⁻¹) which was 47.1 and 16.4% higher as compared to IS₁ and IS₂, respectively.

At 240 DAP, PT planting with trash mulching of 6 t ha⁻¹ (PM₃) resulted in the tallest plants which were 18.9, 21.8, and 4.4% higher as compared to CF planting with mulch (PM₁) or without mulch (PM₂) and PT planting without mulch (PM₄), respectively. Similarly, among the different irrigation scheduling, plant height of the crop was significantly higher in IW/CPE ratio of 1.00 (IS₃; 342.1 cm) as compared to IW/CPE ratio of 0.60 (IS₁; 303.4 cm) and at par with the IW/CPE of 0.8 (IS₂; 332.0 cm; Table 5). Hence, IS₃ enhanced plant height to the tune of 11.3% over IS₁.

The planting method with or without trash mulching and irrigation regimes had a significant (p ≤ 0.05) influence on the yield and its attributes, i.e., cane diameter, weight and millable stalk (Table 6). PT planting with trash mulching (6 t ha⁻¹; PM₃) significantly (p ≤ 0.05) enhanced the cane diameter to the tune of 8.6 and 11.6% over CF planting with mulching and without mulching, respectively. Among the irrigation schedule, the treatment IS₃ recorded a maximum cane diameter (2.41 cm). However, single cane weight was not affected by planting methods with or without trash mulch and different irrigation schedules.

Results showed that the number of millable stalks was highest in the treatment PM₃ which was at par with PM₄ but significantly (p ≤ 0.05) superior to the treatments of CF planting techniques. This PT planting with trash mulching exhibited about 16.0 and 24.4% increments in millable stalk numbers as compared to the millable stalk numbers under the CF planting method with or without trash mulching, respectively. Moreover, the number of millable stalks was significantly (p ≤ 0.05) higher for sugarcane irrigated with an IW/CPE of 1.0 (143,900), as compared to crops irrigated with 0.60 and 0.80 IW/CPE schedules.

In sugarcane production, genotype, management techniques, and environment have a major impact on the yield of the crop. By harvesting at the right time of crop maturity, maximum yields and minimal losses can be achieved. The present study indicated that in PT planting with trash mulching of 6 t ha⁻¹ (PM₃), cane yield (103.5 t ha⁻¹) was significantly (p ≤ 0.05) higher compared to CF planting method. The CF planting treatment produced the lowest cane yield (81.7 t ha⁻¹) compared to the other planting methods and trash management practices. Similarly, among the treatment IS₃ (103.9 t ha⁻¹) significantly (p ≤ 0.05) higher cane yield as compared to other irrigation regime treatments. Furthermore, cane yield was found to be increased by 31.2% and by 9.5% with IW/CPE ratios of 1.00 as compared to treatments with IW/CPE ratios of 0.60 and 0.80 (Table 6). However, juice-quality traits like sucrose content were not significantly (p ≤ 0.05) influenced by all methods of planting with or without trash mulching and irrigation schedules.

Based on pooled data for 3 years (Table 7), significantly (p ≤ 0.05) higher water use efficiency was obtained under PT planting with trash mulching of 6 t/ha (1,049 kg ha⁻¹ cm⁻¹) than the PT planting without trash mulching and was statistically as efficient as the other treatments. A similar trend was observed in water productivity. It was also observed that PT planting with trash mulching resulted in the highest water productivity, accounting for an increase of ~35.9 and 46.6% over the CF planting with or without trash mulching, respectively (Table 1). As well, among the different irrigation scheduling strategies, the highest water use efficiency was associated with IW/CPE of 0.80 (995.4 kg ha⁻¹ cm⁻¹) which was comparable to IW/CPE of 1.00 (964.4 kg ha⁻¹ cm⁻¹) but significantly higher than IW/CPE of 0.60 (p ≤ 0.05). Whereas, water productivity was maximum in treatment IS₃ which was 40.7% higher as compared to the treatment IS₁ (Table 7).

Growth of sugarcane was found to improve under the PT planting method with or without mulch under IW/CPE of 1.00. There is a possibility that this may be due to optimal sugarcane metabolism (Wang et al., 2013), better soil microclimates that allow for root growth, and other favorable conditions for germination (Singh et al., 2019) in comparison with CF plantings. A better root system contributes to a better swelling and sprouting of cane buds. Similarly, in our study, 0.80 and 1.00 IW/CPE ratios enhanced sugarcane germination by maintaining adequate soil moisture around cane setts. Moisture in the soil is essential for this mechanism. Water infiltration into cells produces turgor pressure, which displaces soil particles, overcomes friction, and allows the plant to extend through the soil (Cole, 1939). As roots grow, their apical meristem undergoes cell division and a zone just behind their apex undergoes cell expansion. Root development and germination are therefore dependent on a proper soil moisture regime (Clark et al., 2003; Singh et al., 2022). High daytime temperatures are associated with water stress leading to low growth, high tiller mortality, and low cane yields. However, in our study, planting method and irrigation schedules significantly impacted the tillers at 120 DAP and paired row planting (30:120 cm) row spacing with trash mulching @ 6 t ha⁻¹ produced a higher number of tillers and it was increased by 34.5% than conventional flat planting without mulching this might be due to the reason that paired row planting provided adequate aeration, water and nutrients for the roots, resulting into a greater number of tillers. In addition, trash mulch application may serve to retain water in the rhizosphere for a longer period, thereby retaining soil moisture. According to Singh (2012), PT planting at 105 DAP showed significantly higher tiller counts than furrow-irrigated raised beds. Furthermore, Wiedenfeld and Enciso (2008) report that irrigation water increases soil water potential and the ability of the roots to absorb water, thus controlling hydric balance. Optimal hydrological balance helps maintain stomatal conductance and photosynthetic activity in plants. Furthermore, Kumar et al. (2013) and Dingre and Gorantiwar (2021) found that water use is related to the crop growth demand and soil aeration improves the speed of cell division and elongation. Hence, due to irrigation schedules, the difference in water led to significant variability in plant height.

There was a significant reduction in cane yield with deficit irrigation, showing that water quantity has a direct impact on cane yield. Further, cane yield is directly proportional to water transpiration (Tayade et al., 2020). In this regard, it is necessary to maintain good soil moisture throughout the various growth stages of sugarcane (Dhanapal et al., 2019). In general, it is believed that PT plantings with IW/CPE of 1.00 have higher yield attributes than CF ones with IW/CPE of 0.6 based on factors such as the number of millable stalks, the cane diameter, and the weight of each cane. There may have been an improvement in microclimate conditions as well as less competition for resources in the crop during reproductive stages as a result of better sprouting and tillering of the crop under frequent watering under PT planting with trash mulching under IW/CPE 1.00, which leads to greater cane diameter (Nadeem et al., 2020). As a result of PT planting, synchronized tillers were able to form in this study, which may have facilitated improved soil water conservation, a cooler soil environment, and effective weed control. Adding trash mulch at these rates resulted in significant yield increases in canes that were thicker, heavier, and more desirable in terms of quality. Consistent with our results, Singh and Brar (2015) also reported that paired row trench planting recorded the highest cane diameter, cane weight, and millable stalks. This investigation found that the application of trash as the mulch of (6 t ha⁻¹) could not improve the cane yield significantly as compared to trash mulching in the PT planting system. In contrast, Concenco et al. (2016) and Bassey et al. (2021) found that trash mulch application of 6–9 t ha⁻¹ produced taller plants, thicker cane stalks, higher brix content of sugarcane and higher cane yield. Moreover, Kumar et al. (2015) reported that the tallest plants, maximum tillers, millable canes, average cane weight, and cane yield were observed when trash mulch was applied at 10 t ha⁻¹. This investigation found that irrigation scheduling at an IW/CPE ratio of 1.00 resulted in maximum cane yield. In such circumstances, soil moisture might reach an optimum level during growth periods, leading to better leaf area expansion and photosynthesis, resulting in increased plant growth. A similar observation has been made by Singh and Brar (2015), who also reported a higher yield for crops irrigated at 1.0 IW: CPE than those irrigated at 0.75 and 0.50. Whereas, a significant increase in cane yield was reported by Singh et al. (2007) and Singh (2012) when irrigation scheduling for IW/CPE ratios of 0.75 over 0.50 was used. Moreover, 56% cane yield reduction due to irrigation at 50% CPE as compared to 100% CPE had been reported by Vasantha et al. (2020). In PT plantings with an IW/CPE of 1.00, trash application significantly affected the millable stalks by affecting the emergence and tillering patterns and, in turn, the yield of sugarcane, since it affected the diameter and weight of the canes at a later stage. Whereas, green cane trash blanket reduced the soil temperature and its variability as compared to the bare soil treatment; but did not show difference in evapotranspiration, soil moisture, and growth attributes of sugarcane (Gonçalves et al., 2023).

In this study, we have observed higher water use efficiency and water productivity with trash mulching with an irrigation schedule of 1.00 over non-mulching with IW/CPE of 0.6 and 0.8. This was due to a reduction in irrigation water losses through percolation and evaporation. Increasing yield and reducing irrigation water usage increases water use efficiency and productivity. Similar results findings given by Banerjee et al. (2016). Earlier studies showed that under mulched PT planting, water use efficiency, and water productivity were greater than under no-mulch planting, demonstrating the effectiveness of mulch in reducing soil evaporation and increasing plant respiration (Zhao et al., 1996; Zhang et al., 1999). With an increase in irrigation water applied, water use efficiency decreased, but water productivity increased (Singh and Mohan, 1994; Zhang X. Y. et al., 2005; Singh et al., 2007). The results from our study indicate that surface retention of crop residues reduces water requirements by conserving soil moisture through reduced evaporation losses (Jat et al., 2015; Sandhu et al., 2019). In our study, an increment in water productivity was observed and the increment was 28.9% under IS₃ (IW/CPE: 1.0) over IS₁ (IW/CPE: 0.60). The increase in irrigation amount may lead to a more efficient utilization of light and heat (Zou et al., 2020), resulting in a higher yield. Conversely, an excessive supply of water can result in an excessive use of light and heat, as well as an extended period of vegetative growth and a delayed period of reproductive growth. In addition, excessive irrigation may have caused some deep drainage and leaching of soil nutrients, which resulted in decreased sugarcane production (Fan et al., 2018).

The ultimate goal of agriculture is to maximize economic benefits. It is thus expected that paired row trench planting with trash mulching under IW/CPE of 1.00 should result in increased net returns and B/C ratio because of enhanced cane yield (Showler, 2023) and the results of the present study confirm this. Similarly, as compared to conventional planting of sugarcane, paired-row trench planting showed 34.0% higher returns (Singh and Brar, 2015), while 120 cm PT planting with lentils as intercrop yielded a maximum net return of Rs. 321,254 ha⁻¹ (Nadeem et al., 2020).

The findings of the current investigation showed that the SOC dynamics under different planting methods with trash mulch applications under various irrigation schedules differed significantly. The amount of SOC in post-harvest soil is dependent on the rate of organic matter decomposition and the addition of residual biomass (Yadav et al., 2009). Trash mulch can improve soil organic carbon and consequently improve soil health for longer periods under CF planting or PT planting (Shukla and Yadav, 2011). In contrast, Preet et al. (2022) found that soil organic carbon was slightly decreased with mulching. Nevertheless, Lal (1997) observed that mulching crop residue increased carbon accumulation on clayey Oxisol by 15% after 6 years, which represents 0.65 Mg of C ha⁻¹ year⁻¹ and 14% of mulched carbon. Further, residue retention under a cereal-based cropping system contributed significantly to an increase in SOC stock at 0–30 cm soil depth in South Asia (Chatterjee et al., 2018; Das et al., 2018).

Under planting methods with or without mulching-irrigation modulated conditions, soil enzyme activity may be altered, resulting in alterations in soil characteristics. In this study, it was observed that trash mulching enhances decomposition by altering moisture content, enhancing heat in the topsoil, and stimulating microbial activity. In these treatments, higher soil microbial activities might have resulted from increased moisture leading to fresh residue being added by root biomass, which has boosted soil respiration with irrigation. Alternatively, sugarcane trash could allow nutrients and carbon to slowly release as required by the crop, resulting in reduced losses and a soil C pool that builds over time (Yadav et al., 1994; Sparling et al., 1998). The experimental results revealed that the plots under trash mulching with PT planting accumulate more soil C and, thereby could be reckoned to promote the C sequestration potential of soil (Shukla et al., 2013). Earlier research has shown that organic mulches increase soil organic carbon levels significantly (Saroa and Lal, 2003), with an increase of 33.0% over 10 years (Blanco-Canqui and Lal, 2007). Surendran et al. (2016) found that trash shredding with composted pressmud and application of microbial consortia resulted in higher soil microbial biomass carbon which increased soil available nutrients under a sugarcane planting system. In calcareous arid and semiarid soils with a low percentage of organic matter, mulching materials have been reported to improve soil microbial activity (Khadem and Raiesi, 2017; Mubarak et al., 2021). However, dehydrogenase activity is associated with intact cells of microorganisms and is thought to represent the range of oxidative activities of soil microorganisms (Pramanick et al., 2022). This research suggests that trash mulching in the PT planting might provide a conducive environment for microbe growth, which would increase soil enzyme activity. When soil moisture is adequate, high soil dehydrogenase activity may be achieved because microorganisms develop more rapidly in soil conditions with good oxygen (Stepniewska and Wolinska, 2005; Borowik and Wyszkowska, 2016).

In addition, a significant increase in SOC was observed due to an increase in root biomass due to a positive relationship between SOC dynamics and long-term residue mulching (Maharana et al., 2012; Liu et al., 2014). Moreover, organic carbon content and microbial activity in surface soil increased significantly due to the application of optimum moisture under suitable planting methods helped in increasing biomass production (Tank and Patel, 2013). Accordingly, the complementary effect of trash mulching of 6 t ha⁻¹ with PT planting and irrigation at IW/CPE of 1.00 could be considered a significant practice for raising and sustaining sugarcane productivity as well as soil health.