1 Introduction

Rice (Oryza sativa L.) is considered a supreme commodity for mankind, as it is truly life, a culture, a tradition and a means of livelihood for millions of people and is cultivated under diverse environmental conditions (39° S latitude to 50° N latitude and below sea level to more than 2500 m altitude) in more than 100 countries worldwide. However, 90% of the world’s rice is grown and consumed in Asia, covering 85% of the total area of rice cultivation [1], which in turn tends to feed almost half of the world’s population [2]. From an area of 43.79 Mha with 177.64 MT of production, India ranks second after China in terms of global rice production, with summer rice contributing 14.29 Mt of production and the remaining from wet-season (Kharif) rice [3].

Although wet season (Kharif) rice contributes more (86.42% higher) to summer rice production, but summer rice is known to have greater productivity (23.26% more than kharif rice) [4] due to better crop response to well-managed agronomic practices, more sunshine hours and less disease-causing pest infestations, which facilitate better start-up from earlier stages, greater photosynthate accumulation and, during later stages, increased temperature due to improved grain filling, ripening and ultimately increased rice yield. Despite the aforementioned advantages, the current productivity of summer rice in Eastern India is relatively inadequate [5] and indeterminate because of inappropriate age-old management practices, the dwindling trend of ensuring irrigation facilities, and recent climatic uncertainties, especially temperature variation at the juvenile stage of the crop, which leads to negative net returns [6].

Puddled transplanting is the most dominant and traditional method of establishing irrigated lowland rice in eastern India, facilitating better weed control and reducing percolation loss, but it is also responsible for the breakdown of soil aggregates, macropore destruction [7], and the formation of a hard pan in the subsurface layer [8, 9]. Moreover, it has been well established that 30% of the total irrigation water is required for puddling operations [10, 11];, and in the winter season, farmers depend exclusively on irrigation to mitigate water demand. Therefore, any alternative crop management approach that reduces input usage without compromising rice yield would be a valuable strategy. In this context, nonpuddled transplanted rice (NPTR) may serve as a substitute technique for rice establishment, offering savings in labour, water, and time [12, 13]. Nonpuddled transplanting is the same as conventional transplanting with the omission of puddling operations [14]. Compared with traditional systems, nonpuddled rice has been reported to achieve water savings ranging from 35 to 57% [15, 16]. Moreover, the NPTR does not create hardpan in the subsoil layer and maintains soil aggregates, infiltration pores and other physical properties [17]. However, the performance of rice seedlings under non-puddled condition along with different water regimes and seedbed management is rare in literature.

Agricultural utilizable water is progressively scarce due to global warming, rapid urbanization, and industrialization [18, 19]. Approximately 70% of the world’s freshwater resources are utilized by the agricultural sector for irrigation [20, 21]. An estimated 15–20 million hectares of irrigated rice in Asia are expected to face water shortages by the conclusion of 2025 [22], as it is often cultivated under continuously flooded [23]. Furthermore, rice has a much lower water use efficiency than other crops. On average, a large quantity of water, i.e., approximately 3000–5000 L, is used to produce one kg of rice depending upon the cultivation method [10]. Therefore, the availability of and access to irrigation water are identified as the major constraints on rice-based farming systems. Various water-saving techniques, as well as alternate wetting and drying (AWD) or intermittent irrigation, have been recognized and endorsed for their wider disseminationto decrease water input and increase water productivity [24]. Assessment of AWD and farmers’ water management methods revealed similar yields, but a 19–25% reduction in water use with AWD was detected with a greater economic return [25].

Seedling age at the time of transplanting is another crucial factor in determining uniform plant stands and regulating growth and yield [26]. One of the major reasons for delayed transplanting in summer rice is the occurrence of low-temperature stress at the time of nursery seeding, which inhibits seedling emergence and establishment and gradually leads to stunted growth and discolouration or even complete failure in the main field [26]. In Asian and Southeast Asian countries, approximately 7 million hectares of capable land for rice cultivation remain unutilized because of significant injury to seedlings caused by chilling stress [27]. Moreover, summer rice is susceptible to terminal thermal stress and tropical cyclones during maturity, typically occurring from March onwards as a result of late transplanting, accounting for 45% of yield loss globally [28].

Therefore, transparent polythene covering with an appropriate height is an effective management tool because it functions as a greenhouse, regulating diurnal temperature differences and optimizing internal temperatures [29, 30], defends humidity loss straight out of the ground surface, and regulates weed appearance [31, 32]. As a result, it enhances the efficiency of humidity and nutrient utilization by seedlings while preventing chilling stress [33, 34]. Moreover, implementing this adapted set of techniques and methods, drawn from the prevailing data pool, reduces the duration required for raising seedlings. Younger seedlings, resulting from this approach, contribute to robust crop growth, improved tillering behaviours, favourable yield attributes, and increased rice yield. They tend to eliminate transplanting shock at a faster rate, efficiently absorb soil nutrients, and exhibit greater resistance to disease and pest infestations than their older counterparts [35,36,37].

There have been few previous works that emphasize economically affordable and easily adaptable alternate methods of rice cultivation by addressing prevailing weather irregularities and scarce resources. However, rice cultivation methodology including establishment methods, water application strategies along with embolden climate resilient rice seedlings production is completely absent in previous reports. Therefore, this study was undertaken to develop a comprehensive rice cultivation technique that could improve soil health along with low water use without compromising productivity and profitability under changing climatic scenario.

2 Materials and methods

2.1 Experimental site

A field experiment was performed at the Central Research Farm, BCKV, and Gayeshpur, under Bidhan Chandra Krishi Viswavidyalaya, West Bengal, India (23°8́ʹN latitude and 88° E longitudes with an average altitude of 9.75 m above mean sea level), in the winter seasons of 2017–2018 and 2018–19. The farm is situated within the New Alluvial Zone of West Bengal. The site of the experiment was situated in a typical subtropical climate marked by a hot and moderately humid summer, a warm and humid rainy season, and an extremely dry and cold winter. The maximum and minimum temperatures varied between 37.0 and 6.4 ℃ and 34.9–5.7 ℃ in 2017–2018 and 2018–19, respectively (Fig. 1). There was a consistent decrease in temperature from December to January in both growing seasons. The maximum and minimum humidities of the experimental area ranged between 95% and 47.4% in 2017–2018 and between 93.8% and 45.4% in 2018–2018 (Fig. 1).

Fig. 1
figure 1

Meteorological observations of temperature and rainfall (a, c) and relative humidity and sunshine hours (b, d) during the experimental periods of 2017–2018 and 2018–2018

Full size image

Heavy rainfall commences from the middle of June and continues through September because the south‒west monsoon and winter season rainfall mainly occur through western disturbance. Total rainfall amounts of 16.9 and 25.5 mm were received during the 2017–2018 and 2018–19 periods, respectively, of the experiment (November–March). The most bright sunshine hours were detected in March in each of the years of the experiment. The corresponding minimum sunshine hours were recorded in December. The experimental field consisted of sandy loam soil with a relatively high water retention capacity (WHC), neutral pH, low organic carbon, and available N but medium available P and K.

2.2 Experimental design

The experiment was performed in a strip-split plot design with three replications. The main plots included two treatments, viz., puddled transplanted rice (PTR) and nonpuddled transplanted rice (NPTR), while the subplot consisted of three treatments, viz., 3, 6 and 9 days after irrigation application, and the subsubplot consisted of two different methods of seedbed management, namely, conventional seedbed and improved seedbed management, i.e., seed bed protection with polythene (transparent, 30 microns) cover. The details of methodologies for seedbed preparation was reported by Mondal et al. [38].The size of each experimental subsubplot was 6 m × 4 m, and the plots were separated by a minimum of 1 m bunds to avoid seepage losses. Plastic lining was applied around the subplots by digging them 40 cm deep. Rice seedlings were transplanted at a 20 cm row-to-row spacing and 15 cm plant-to-plant distance during both years.

2.3 Field preparation

In the main field, the required amount of well-decomposed FYM was applied 2 weeks before transplanting. For PTR, a total of 3–4 ploughing events were performed, followed by one laddering, and 5–7 cm of water was maintained for the next week to check the weed population and full decomposition of stubble and applied FYM. After that, 2–3 ploughings followed one laddering was given to level the uneven land for uniform distribution of irrigation water, easy and efficient seedling transplanting. In the case of the NPTR, two ploughing through rotavator was given and the ground was presoaked a day before transplanting to make the soil softer and to ease the transplanting process. On the day of transplanting the field was flooded and transplanting was carried out in flodded condition. In the case of conventional seedbed management, 40-day-old seedlings (2–3 hill−1) were transplanted, and in the case of improved seedbed management, 25-day-old seedlings (single hill−1) were manually transplanted within the 3rd week of January. The recommended dose of fertilizer (RDF), i.e., 100:50:50 kg N, P and K, was provided using urea, single superphosphate (SSP), and muriate of potash (MOP), respectively. Approximately 25% of the N, the total amount of P, and 50% of the K were provided during final land preparation. The remaining nitrogenous fertilizer was applied in two splits, i.e., 50% at active tillering and 25% before the panicle initiation stage. The remaining 50% of the potassic fertilizer was also applied during the PI stage. Bispyribac sodium 10% SC (Nominee Gold) was applied postemergence at a rate of 200 ml per hectare 15 days after transplanting (DAT), followed by hand weeding (HW) at 42 DAT to facilitate early crop growth through weed control. All other agronomic packages and practices adhered to recommended standard procedures. Harvesting took place during the 3rd week of April in both growing seasons.

2.4 Water application

Polyvinyl chloride pipes (10 cm diameter) were used to apply irrigation water to each plot according to treatment, and the volume of water was assessed with a flow meter (Dasmesh Co., India). During each instance of water application, the plots were filled to a standing water depth of 50 mm, as measured using a ruler installed in each plot. The amount of water applied was calculated by dividing the irrigation volume by the plot’s area and then converted to millimeters.

2.5 Measurements and analytical procedures

2.5.1 Growth attributes

Destructive sampling was designated for the second rows on both sides, while the recording of additional biometric observations and the assessment of yield attributes were assigned to the remaining rows. Five hills from the central two rows were chosen randomly from each plot, and at the point of maturity, the plantswere harvested and dried, and the yield was documented. The samples were collected at different stages of growth at 18-day intervals from transplanting up to 72 DAT and before harvesting. Plant height was measured from the ground surface to the tip of the leaf. To document biomass production, five plants from the second-to-last rows within each plot were meticulously uprooted, thoroughly cleansed, and left to air dry. Subsequently, the samples were segregated into stem, leaf, and root components and then subjected to oven drying at 70 ℃ until a consistent dry weight was achieved. The total aboveground biomass was determined by summing the biomasses of the leaves and stems and was ultimately reported in grams per square meter (g m−2). The crop growth rate (CGR) was determined using the following formula [30]:

$$\text{CGR}=\frac{{\text{W}}_{2}-{\text{W}}_{1}}{{\text{T}}_{2}-{\text{T}}_{1}}\times \frac{1}{\text{GA}}\text{g}/{\text{m}}^{2}/\text{day}$$

where W2 and W1 represent the ultimate and initial biomass of plant material per unit area at times T2 (final time) and T1 (initial time), respectively. GA denotes the ground area in square meters (m2). “The leaf area index was measured by dividing the total leaf area of a plant by a respective ground area. To determine tiller density, two 60 cm long consecutive rows at two locations were tagged. Every time the tagged area was considered for counting tillers, tiller density was calculated by converting it to a m2 basis.

2.5.2 Yield attributes and yield

The number of panicles was counted from the five hills of central two rows in each plot manually, and the mean value was converted into panicle m−2. Twenty abaxial panicles were collected to determine the quantity of unfilled grains and filled grains/panicles separated from unfilled grains. The collected panicles were measured manually by a measuring scale to determine panicle length. The test weight was determined by randomly counting a thousand grains from each plot, and the weight was recorded on a 14% moisture basis and is expressed in g.

The grain yield was determined by cutting the plant sample from a net plot area of 6 m2 (3 m × 2 m) from the middle of each plot. Samples were harvested, tied in bundles and then taken to the threshing floor for drying, threshing and measuring the grain and straw yield. The yield was expressed as t ha−1 at 14% moisture content. The harvest index was calculated by dividing the grain yield by the total biomass yield.

2.5.3 Water productivity

The irrigation water productivity was assessed by dividing the grain yield by the amount of irrigation input. Input water productivity was determined by dividing the grain yield by the total irrigation water and rainfall received during the crop growing period.

2.5.4 Determination of soil moisture content

Soil sampling was performed from each plot with the help of a tube auger at 0 to 15, 15 to 30, 30 to 45 and 45 to 60 cm depths, and the soil was assessed by a digital weighing machine. The collected samples were desiccated in a forced-air oven at 105 ℃ for 24 to 48 h to attain a consistent equilibrium weight. Then, the dry soil samples were weighed. The gravimetric moisture content was determined with the help of the following formula:

$$\text{Moisture content }\left(\text{\%}\right)=\frac{\text{Wet weight}-\text{Dry weight}}{\text{Dry weight}}\times 100$$

2.5.5 Statistical analysis

The data derived from the experiment were analysed through an analysis of variance (ANOVA) technique employing the Statistical Tool for Agricultural Research (STAR). (Statistical Tool for Agricultural Research; IRRI 2014). Significantly different means were separated at the 0.05% or 0.01% probability level by Duncan’s multiple range test (DMRT).

3 Results

3.1 Growth attributes

The height of the plants in the PTR treatment was significantly greater than that in the NPTR treatment up to 36 DAT in 2017–2018. However, greater plant height was measured in the NPTR at harvest in both seasons of the experiments (Fig. 2a and d). The plant height increased with the application of irrigation at 3-day intervals, followed by irrigation at 6-day intervals, at different periods of observation irrespective of the growing season (Fig. 2b and e). In the case of seedbed management practices, compared with the improved method, conventional practices resulted in greater plant heights up to 36 DAT, after which plant heights decreased significantly (p ≤ 0.05) (Fig. 2c and f). A significantly (p ≤ 0.05) greater maximum tiller count was detected in the PTR treatment than in the NPTR treatment at 18 DAT in year 1; however, no significant variation was detected at subsequent growth stages. During the second year of the study, rice under the NPTR had the highest tiller density (Fig. 3a–d).

Fig. 2
figure 2

Effect of crop establishment methods (a, d), irrigation regimes (b, e) and seedbed management practices (c, f) on the height of summer rice plants. Error bars represent the least significant difference (p ≤ 0.05) values

Full size image
Fig. 3
figure 3

Effect of crop establishment methods (a, d), irrigation regimes (b, e) and seedbed management practices (c, f) on the tiller density of summer rice. Error bars represent the least significant difference (p ≤ 0.05) values

Full size image

Among the irrigation management practices, tiller density continuously increased up to 72 DAT under the 3-day and 6-day intervals of irrigation; however, under the 9-day interval of water application, tiller density decreased to 72 DAT (Fig. 3b and e). The most tillers were recorded after 3 days of watering, closely followed by 6 days of watering, irrespective of the studied year. There was no significant difference in tiller count among the seedbed management treatments at 72 DAT, while up to 36 DAT, the maximum tiller density was recorded for the conventional seedlings, and at 54 DAT, it was highest for the improved seedlings (Fig. 3c and f). Similar to the aforementioned growth attributes, rice accumulated more biomass from the aboveground part under the NPTR with 6-day irrigation intervals and improved seedlings at the time of harvesting in both years (Fig. 4).

Fig. 4
figure 4

Effect of crop establishment methods (a, d), irrigation regimes (b, e) and seedbed management practices (c, f) on the aboveground biomass accumulation of summer rice. Error bars represent the least significant difference (p ≤ 0.05) values

Full size image

The crop growth rate (CGR) significantly (p ≤ 0.05) varied with establishment methods, irrigation regimes and seedbed management practices at different growth stages of rice, and for each factor, the CGR increased with increasing growth rate up to 72 DAT and thereafter declined (Fig. 5). A parallel trend was observed for the leaf area index (LAI) (Fig. 6).

Fig. 5
figure 5

Effect of crop establishment methods (a, d), irrigation regimes (b, e) and seedbed management practices (c, f) on the crop growth rate of summer rice. Error bars represent the least significant difference (p ≤ 0.05) values

Full size image
Fig. 6
figure 6

Effect of crop establishment methods (a, d), irrigation regimes (b, e) and seedbed management practices (c, f) on the leaf area index of summer rice. Error bars represent the least significant difference (p ≤ 0.05) values

Full size image

3.2 Yield attributes and yield

The effects of the different treatments on yield-related traits such as panicle m−2, filled grain panicle−1, panicle length and test weight are summarized in Table 1. There was a significant interaction effect of establishment method, irrigation regime, and seedbed management on panicle count and filled grain panicle−1.

Table 1 Effect of establishment methods, irrigation regimes and seedbed management on yield attributes and yields of summer rice
Full size table

In both years of experimentation, the maximum number of panicles was counted from NPTR over PTR, although the number of panicles varied nonsignificantly from one another (Table 1). Similarly, nonsignificant variation was observed in the number of filled grains panicle−1, panicle length and test weight among the crop establishment methods, irrespective of the years studied. Irrigation application at 3-day intervals resulted in maximum panicle counts (447 and 454), which were statistically similar to those at 6-day irrigation intervals (442 and 435) during year 1 and year 2, respectively. The lowest number of panicles was counted after 9 days of irrigation.

However, plants transplanted from improved nurseries had 3.20% and 4.12% more panicles than did plants transplanted from conventional plants. The number of filled grains per panicle significantly (p ≤ 0.05) differed among the different irrigation regimes and decreased with increasing irrigation interval. The most frequent watering of rice resulted in a maximum number of filled grains per panicle (107 and 111 in year 1 and year 2, respectively), and the lowest number of filled grains occurred at the 9-day irrigation interval, accounting for 71 and 68, respectively, in both years. However, seedbed management did not significantly influence the number of filled grains per panicle. Significantly (p ≤ 0.05) greater panicle length and test weight were measured after 3 days of watering, followed by 6 days and 9 days of irrigation in year 1 and year 2, respectively. In both cases, variation due to seedbed management was absent.

It is evident from Table 1 that both grain yield and straw yield varied nonsignificantly among PTRs and NPTRs. Irrigation at 3-day intervals had the greatest effect (6.09 t ha−1 and 6.05 t ha−1 in year 1 and year 2, respectively), which was statistically similar to that at the 6-day irrigation interval but varied significantly with the 9-day irrigation interval. A similar trend was also observed for straw yield. The treatment combination (crop establishment × irrigation regimes × seedbed management) significantly influenced the grain yield and straw yield irrespective of the studied year (Table 1).

3.3 Moisture distribution

The soil moisture content (%) varied with different planting methods, irrigation regimes and seedbed management practices at various growth stages of rice. active tillering, panicle initiation, flowering, grain filling and physiological maturity (Figs. 7, 8, 9, 10 and 11). Among the different crop establishment methods, the soil moisture content of rice plants transplanted under puddled conditions was greater than that under nonpuddled conditions at each measured growth stage. Moreover, moisture storage under PTR was 4.58% and 5.39% greater than that under NPTR at 0 to 15 cm and 15 to 30 cm soil depths, respectively, during the first year at the active tillering stage (Fig. 7a and d). However, 0.58% and 1.66% greater moisture storage occurred in the PTR than in the NPTR at the two lowermost depths. A similar trend was observed at panicle initiation, flowering, and grain filling and at the physiological maturity stage. In each growth stage, the difference in moisture between the two crop establishment methods was greater at the upper two depths, and the difference in moisture decreased with increasing soil depth. However, during the time of physiological maturity, the moisture difference was almost the same at each soil depth because of the withdrawal of irrigation 15 days before harvesting. Among the irrigation regimes, frequent watering at 3-day intervals always resulted in a significantly (p ≤ 0.05) greater soil moisture content than did the other treatments. During active tillering, 75.09% and 79.00% moisture was retained in the 0–15 cm soil layer in years 1 and 2, respectively, where the 6-day intervals contained 69.72% and 73.91% moisture, respectively, and the 9-day intervals contained 67.03% and 66.63% moisture, respectively, during both years (Fig. 7b and e).

Fig. 7
figure 7

Effect of crop establishment methods (a, d), irrigation regimes (b, e) and seedbed management practices (c, f) on soil moisture content (%) at active tillering. Error bars represent the least significant difference (p ≤ 0.05) values

Full size image
Fig. 8
figure 8

Effect of crop establishment methods (a, d), irrigation regimes (b, e) and seedbed management practices (c, f) on soil moisture content (%) at panicle initiation. Error bars represent the least significant difference (p ≤ 0.05) values

Full size image
Fig. 9
figure 9

Effect of crop establishment methods (a, d), irrigation regimes (b, e) and seedbed management practices (c, f) on soil moisture content (%) at the flowering stage. Error bars represent the least significant difference (p ≤ 0.05) values

Full size image
Fig. 10
figure 10

Effect of crop establishment methods (a, d), irrigation regimes (b, e) and seedbed management practices (c, f) on the soil moisture content (%) at the grain filling stage. Error bars represent the least significant difference (p ≤ 0.05) values

Full size image
Fig. 11
figure 11

Effect of crop establishment methods (a, d), irrigation regimes (b, e) and seedbed management practices (c, f) on soil moisture content (%) at physiological maturity. Error bars represent the least significant difference (p ≤ 0.05) values

Full size image

The difference in soil moisture among the three irrigation regimes was greater at the two uppermost depths (0–15 cm and 15–30 cm), and the difference was negligible at the lowermost soil depth. A similar trend was recorded at subsequent stages. During panicle initiation (Fig. 8b and e), the low soil moisture status, irrespective of the soil profile and year of experimentation, was accounted for compared to that during active tillering, possibly due to the higher moisture requirements of the crop.

A similar trend was recorded at the flowering stage (Fig. 9b and e). However, at grain filling, the soil moisture content at the studied depths was greater than that at the previous two crop growth stages. Soil moisture storage was significantly (p ≤ 0.05) greater in the plot where rice plants were transplanted from an improved nursery bed during active tillering, irrespective of the soil depth and year (Fig. 7c and f). A similar trend was recorded for panicle initiation (Fig. 8c and f) and flowering (Fig. 9c and f). In contrast, during grain filling (Fig. 10c and f) and physiological maturity (Fig. 11c and f), significantly (p ≤ 0.05) greater moisture storage was obtained from the experimental units where conventionally raised plants were transplanted.

3.4 Water productivity

The variation in water productivity (both irrigation and input) due to the crop establishment method was nonsignificant in both years of experimentation (Table 2). Among the irrigation regimes, rice plants irrigated at 9-day intervals had significantly (p ≤ 0.01) greater irrigation water productivity (8.80 and 9.40 kg ha−1 mm−1) than those irrigated at 6-day intervals (8.50 and 8.64 kg ha−1 mm−1) and 3-day intervals (4.87 and 4.81 kg ha−1 mm−1) during year 1 and year 2, respectively. A similar trend was also observed for input water productivity. Rice plants transplanted from improved seedbeds exhibited significantly (p ≤ 0.01) greater irrigation water productivity, accounting for 3.97% and 4.21% more plants transplanted from improved seedbeds, respectively, than those transplanted from plants transplanted via the conventional method for two consecutive years. The variations in input water productivity among seedbed management practices were statistically similar to each other in the 1st year of the study, while in the subsequent year, greater (4.25% over conventional) input water productivity was found from improved seedbeds, which exhibited statistical variation from conventional seedbeds (Table 2). The treatment combination (crop establishment × irrigation regimes × seedbed management) did not significantly influence water productivity in the present study, irrespective of the studied year.

Table 2 Effect of establishment methods, irrigation regimes and seedbed management on the irrigation water productivity and irrigation water productivity of summer rice
Full size table

3.5 Macronutrient (N, P and K) uptake

It is evident from Fig. 12a–d that macronutrient uptake by grain, as well as straw, did not vary significantly due to crop establishment methods in the 1st year of experimentation, while during the 2nd year, contrasting results were observed where significantly (p ≤ 0.05) greater nitrogen uptake (by both grain and straw) was recorded from PTR, accounting for 3.85 and 4.32% more of the grain and straw, respectively, than from NPTR. Similarly, significantly (p ≤ 0.05) greater straw P uptake (6.44% greater) was obtained in the PTR treatment than in the NPTR treatment, but no significant difference was found in grain uptake (Fig. 12a and d). Rice grown under puddled conditions resulted in greater K uptake by grain (105.12 kg ha−1) as well as straw (33.65 kg ha−1) than did rice grown under nonpuddled conditions. The irrigation interval significantly (p ≤ 0.05) influenced plant nutrient removal in both years. The maximum uptake by grain as well as straw was measured after 3 days of irrigation and continuously decreased with increasing water stress (Fig. 12b and e). It was observed that among the 3-day and 6-day irrigation intervals, no significant difference was detected in the grain or straw N uptake. Almost 29% and 25% greater P uptake by grain was recorded under the most frequent water application (3-day intervals) than under subsequent intervals (6-day intervals), with significant variation during year 1 and year 2, respectively. A similar trend was found for straw P uptake and K uptake. The maximum N, P and K uptake, irrespective of plant parts and years of experimentation, was measured for the plants transplanted from the improved seedbed (Fig. 12c and f). Greater removal of grain N (7.26% and 6.97%), P (1.11% and 10.56%) and K (6.44% and 6.13%) by improved plants occurred in two consecutive years. A similar observation was also registered for straw uptake.

Fig. 12
figure 12

Effect of crop establishment methods (a, d), irrigation regimes (b, e) and seedbed management practices (c, f) on nutrient uptake by summer rice. Error bars represent the least significant difference (p ≤ 0.05) values

Full size image

3.6 Economics

The economics of summer rice production under various planting methods, irrigation regimes and seedbed preparation techniques are depicted in Table 3. Gross and net returns were greatest under the NPTR over the PTR for both years of experimentation. The maximum benefit-to-cost ratio was obtained for nonpuddled transplanted rice (1.73 and 1.92 in 2017–2018 and 2018–19, respectively) compared to that for puddled transplanted rice. The rice plants irrigated at 6-day intervals earned a maximum profit in terms of gross returns, net returns and the benefit:cost ratio. Compared with conventional management, crop establishment, irrigation regimes, and improved seedbed management had 19.46% and 14.35% greater net benefits during year 1 and year 2, respectively (Table 3). A parallel trend was also documented in the benefit‒cost ratio.

Table 3 Effect of establishment methods, irrigation regimes and seedbed management on the economics of summer rice production
Full size table

4 Discussion

4.1 Growth attributes

The plant height under PTR was significantly greater than that under NPTR at the initial stages of growth (Fig. 2a and d). This result is in line with the findings of Singh et al. [39], who reported that plant height in transplanted rice is significantly lower under nonpuddled conditions, possibly due to the greater transplanting shock imposed on seedlings in nonpuddled soil [40]. However, NPTR had a greater effect on plant height at later growth stages of rice in both years. Plant height decreased with increasing water scarcity (Fig. 2b and e), possibly because of the inhibition of cell division [41, 42]. However, Pradhan et al. [43] reported a greater plant height under intermittent flooding (99.57 cm) than under continuous flooding (97.12 cm), although no significant difference was detected between the treatments. In the present investigation, greater plant height was observed in conventionally grown plants at the initial stages, possibly due to the greater age of transplantation (40–45 DAS) (Fig. 2c and f). However, seedlings grown with improved methods were taller at later growth periods in the main field because of good seedling vigour because single plants are able to utilize natural resources [44]. This hypothesis also agreed with that of Begum et al. [33], who studied the tallest plant (113.03 cm) with plants grown in polythene covering compared to those grown without poly covering (107.75 cm).

The maximum tiller density was found in the PTR over the NPTR (although it varied nonsignificantly) in the 1st year, while contradictory results were observed in the 2nd year (Fig. 3a and d). Our findings are consistent with those of Sahu et al. [45], who reported a 29% greater tiller count in puddled conditions than in nonpuddled conditions. In contrast, Islam et al. [46] reported a greater tiller count in rice grown under single-pass tillage than under conventional puddling at 70 DAT. Improved nutrient availability under unpuddled transplanting may favour better tillering ability as a consequence of early rooting vigor or better nutrient uptake efficiency [47, 48]. Frequent irrigation application accounted for the maximum tiller count in 2 years of studies (Fig. 3b and e). Uniform results were obtained by Baroudy et al. [49], who suggested that the incidence of soil moisture stress disturbs many physiological procedures and results in poor tillering ability. This mainly occurred due to the water deficit at the critical crop water requirement stage in the rice plants. This result was consistent with the findings of Sarvestani et al. [42] and Rabindra et al. [50]. Plants from conventional seedbeds had greater tiller counts than plants from conventional seedbeds because of greater seedling density (2–3 seedlings hill−1) in the conventional system. However, the tiller count reached a maximum under the improved method from 54 DAT to harvest (Fig. 2c and f). Lampayan et al. [44] concluded that greater seedling competition during late transplanting was inversely proportional to rice tiller production. They also observed more tillers and leaves in plants with a lower seedling density, which was also in line with the findings of Adhikary et al. and Sarwa et al. [51, 52]. The greater number of tillers from younger plants than from older plants might be the consequence of less root damage and minimal transplanting shock imposed on younger plants, which can more easily establish themselves after transplanting in the main field [53].

Above-ground biomass accumulation (Fig. 4a and d) and LAI (Fig. 6a and d) were initially lower in nonpuddled transplanted conditions than in traditional puddled systems. A similar result was also reported by Kar et al. [4], which could be attributed to the delayed early growth of rice from the NPTR, possibly due to root damage throughout the time of transplanting in shallow tilapia nonpuddled soil [40, 54,55,56]; and. In contrast, Sudhir-Yadav et al. [10] reported a lower LAI from PTR; however, at later growth stages, no significant difference was found between PTR and DSR. However, Kar et al. [4]reported better biomass accumulation and LAI at the time of harvesting from nonpuddled conditions than did the traditional method, which also supports our findings. Our results are strongly supported by those of Kar et al. [4] and Sudhir-Yadav et al. [10], who reported lower LAI values with greater moisture tension. The lower LAI was also possibly because of both limited water availability and iron deficiency. The poly-cover-protected seedlings attained a better LAI than did the unprotected conventional seedlings in the main field because the polythene covering protected the plants from cold injury and provided good vigour (Fig. 6c and f). Shah et al. [57] proved that a higher temperature under polythene covering was beneficial for producing healthier seedlings in the nursery bed. They also reported the suitability of rice leaf emergence under greenhouse conditions, as temperature, humidity, light intensity and carbon dioxide concentration between the cover were more beneficial than the outside atmosphere. Throughout the growth period, biomass accumulation and LAI decreased significantly with increasing water stress (Figs. 4 and 6). Similar results were reported by Sudhir-Yadav et al. [10], Belder et al. [58] and Bowman and Toung [20]. Due to the greater plant density in the main field of conventionally raised plants, the dry matter content and LAI were greater at the early growth stage. However, at advanced stages, other growth-attributing traits, such as greater plant height and greater tiller count, result in greater biomass accumulation in rice transplanted from improved nursery beds. Seedling age was also an important factor for aboveground biomass accumulation. Lampayan et al. [24] reported greater biomass accumulation (12.7 t ha−1) in twenty-day-old plants than in thirty-day-old plants. Similar conclusions were also described by Mishra and Salokhe [35], who hypothesized that early transplantation would improve seedling vigour in the main field and quickly recover from transplanting shock, while aged plants would experience more intense transplanting shock.

In earlier stages, a better crop growth rate was recorded from traditional PTR; however, a superior growth rate from the nonpuddled plot was observed from 54 DAT to crop harvesting (Fig. 5a and d). These results were a consequence of dry matter accumulation by rice plants under various crop establishment methods. The crop growth rates with irrigation intervals were also influenced by the aboveground biomass content at different growth stages, and the intermittent application of water resulted in a greater CGR at later growth stages (Fig. 5b and e). These results are in line with those of Sun et al. [59] and Sun et al. [60]. Our experimental findings regarding the effect of seedbed management practices on the rice CGR were the same as the observations of Begum et al. [33], who also reported that the greater growth rate from polythene-protected nursery beds might be due to the healthy vigour of rice plants at the optimum temperature and relative humidity.

4.2 Yield attributes and yield

The yield-attributed traits, namely, panicles per m2, panicle length, filled grain per panicle and test weight, were not significantly influenced by the crop establishment method. Similar observations were also made for grain and straw yield (Table 1). Haque et al. [47] also observed statistically similar panicle counts and rice grain yields during the Rabi season among nonpuddled shallow tillage and conventional puddled conditions. Various former studies on minimum tillage also reported crop yields comparable to those of traditional full tillage systems [9, 61, 62]. The authors did not find any significant difference among tillage treatments for the two boron seasons, even for the harvest index. In an alternative experiment, Haque and Bell [48] noted an absence of variation in panicle length across diverse tillage treatments. Comparable observations were likewise documented in the context of 1000-grain weight assessments conducted during the winter season. The yield reduction under the traditional puddle system might be due to the attenuation of soil structure, the formation of subsurface compaction, and the heightened susceptibility to waterlogging [63]. In a previous experiment, Ladha et al. [64] reported that the introduction of nonpuddled transplanting into minimum-tilled soil resulted in a mean increase in rice yields in agricultural plots of 0.3 metric tons per hectare, which is consistent with our empirical results. This phase of initial yield reduction is frequently addressed through strategic agronomic management and meticulous crop selection, as posited by Baker and Saxton [65]. Consequently, it is imperative to ascertain the specific conditions influencing the increase or decrease in yields under the nonpuddled transplanting regime. The higher grain and straw yield from the 3-day irrigation interval could be attributed to better yield components, such as panicle count, panicle length, filled grain per panicle and test weight, under the same treatment (Table 1). Similar findings were reported by Sarvestani et al. [42], who reported that the manifestation of soil-induced moisture stress impacts physiological processes, leading to suboptimal grain filling. As the interval for irrigation increased from 3 to 9 days, the yield progressively deteriorated. This could be described by decreased chlorophyll content, a decrease in cell volume, cell division, and intercellular spaces, and thickening of the cell wall with an increase in stress due to electrolyte outflow and hence a decrease in yield [66,67,68] ( Implementing intermediate watering intervals with reduced temporal duration has demonstrated the potential to augment photosynthetic processes during subsequent growth stages. This practice enhances carbon remobilization from vegetative tissues to grains, elevates root biomass, and is correlated with heightened yields and increased nutrient uptake [69]. The maximum number of panicles, length of panicles and test weight, as well as the crop yield per unit area, were measured for the plants grown under a polythene-protected seedbed and transplanted at an early age (Table 2). Similar results were also reported by Begum et al. [33], who reported a greater number of panicles per hill from polythene-protected plants and greater crop yield than from traditional plants. They suggested that a better growth environment under polythene protection produced emboldened rice seedlings even under very low temperatures. The benefits of polythene covering on crop performance were also reported by Mondal et al. [30] and Mondal et al. [31]. Additionally, delayed seedling growth in a nursery bed and, therefore, the use of old seedlings prolong the duration of rice growth, which adversely affects yield. Older plants usually recover from transplanting shock more slowly, and the tillering ability of rice increases if younger plants are used [70]. Azhiri-Sigari et al. [71] reported better yield attributed to traits such as the number of panicles per hill, the number of filled grains per panicle and the 1000-grain weight of plants transplanted to main fields at a younger age than older plants. These findings support our experimental findings in which better yield attributes and yields were obtained from plants transplanted from improved nursery beds. The advantages gained by transplanting rice seedlings at an earlier developmental stage have been substantiated by various investigators [72, 73]. This method leverages the observation that the initial phyllochron stages, specifically those with fewer than four leaves, exhibit the possibility of generating a greater number of effective tillers per plant [35]. Furthermore, greater nutrient absorption by younger plants and their full utilization due to better root structure might be another reason for their superior yield-related characteristics and grain yield. The present results indicated that single plants transplanted from improved seedbeds had better grain yields, possibly because of the greater number of panicles per unit area, greater 1000-seed weight and a greater reduction in the number of nonbearing tillers per plant [36].

4.3 Soil moisture status

The soil moisture content was greater in puddled transplanted plots than in nonpuddled plots (Figs. 7, 8, 9, 10 and 11). The creation of a pseudoimpervious layer in subsoil during puddling prevents the deep percolation loss of water, which might be the reason for better water storage in puddled transplanted plots. The plots irrigated at frequent intervals had greater soil moisture storage, possibly because of the greater number of irrigations delivered between crop growth stages. Our results are also in line with those of Pascual and Wang [74]. The least moisture storage and profile moisture were obtained from the 9-day irrigation interval because a lower number of irrigations were applied in a specific time interval. The soil moisture at an earlier stage was greater in the plots where the plants were transplanted from improved seedbeds, while at later growth stages, it was greater in the plots transplanted with conventional seedlings. The higher biomass accumulation and better crop yield from improved seedlings at the later crop growth stage accounted for the greater evapotranspiration from soil moisture, thus resulting in low moisture storage. The soil moisture dynamics during the initial crop developmental phases were predominantly governed by topsoil evaporation. However, as crops progress into the reproductive stage and beyond, variations in soil moisture become intricately associated with crop evapotranspiration [75]. The difference in soil moisture content among the various treatment combinations was greatest in the upper layer and least at lower depths because the active root zone depth reached 45 cm, and better crop development resulted in a greater transpiration rate and lower moisture storage. Our findings are also supported by Mondal et al. [30].

4.4 Water productivity

Water productivity in the present experiment was influenced by the grain yield of rice, as the all-experimental units received the same amount of rainfall and treatmentwise irrigation water. This finding was also supported by Duttarganvi et al. [76]. Water productivity (both irrigation and input water) was greatest under the 9-day irrigation interval, followed by the 6-day and 3-day irrigation intervals (Table 2). These results are in agreement with those of Ceesay et al. [77], Shantappa et al. [78] and Pascual and Wang [74], who reported higher water productivity from intermittent irrigation applications than from traditional flooding systems. An intermittent water application strategy was developed for water-scarce conditions where water is insufficient to keep paddy fields flooded without compromising crop yields, thereby increasing water productivity.

4.5 Nutrient uptake

Alterations in nutrient accessibility and soil compaction under nonpuddled transplanting may enhance rooting vigour and optimize nutrient uptake efficiency [47], which might be the reason for greater nutrient removal by rice under nonpuddled transplanting conditions. A similar observation was also published by Haque and Bell [48]. The increase in nutrient uptake (grain as well as straw) was greater at higher moisture regimes, which was due to the cumulative effect of the increase in grain and straw yield as well as increased nitrogen content (Fig. 12b and e). Additionally, adequate soil moisture accelerates the rate of nutrient solubilization; therefore, more nutrients are available to plants. This result is confirmed by the findings of Sandhu and Mahal [79]. A similar increase in nitrogen uptake with increasing moisture regime was reported by Belder et al. [58], Murthy and Reddy [80], Sandhu and Mahal [79] and Nayak et al. [81]. Our study suggested that intermediate application of irrigation water (at 6-day intervals) resulted in statistically similar nitrogen uptake by rice grain and straw. A similar suggestion was also given by Hameed et al. [82]. The larger surface area of roots due to the favourable root-attributing traits of plants transplanted from polythene-protected seedbeds helps to improve the acquisition of nutrients from the soil [35], supporting our experimental findings (Fig. 12c and f). Moreover, the greater biomass accumulation and grain and straw yields under improved seedbed management also significantly influenced nutrient uptake by the plants.

4.6 Economics

In the current investigation, nonpuddled transplanting (NPTR) demonstrated a superior gross margin in comparison to conventional transplanting into puddled soil, attributable to reduced expenditures incurred under nonpuddled conditions. Similarly, Haque and Bell [48] reported a 30% lower land preparation cost under nonpuddled shallow tillage than under conventional tillage. Indeed, nonpuddled transplanting (NPTR) effectively decreased the time requirements for field preparation and crop establishment, concurrently reducing the frequency of irrigation needed to achieve soil saturation before land preparation. Among the irrigation levels, intermittent water application (at 6-day intervals) had a greater net return and benefit:cost ratio than did the other treatments. The lower amount of irrigation with satisfactory yield (statistically similar to most frequent irrigation) might be the reason behind this. These findings were also in line with those of Singh et al. [83]. A low cost of cultivation along with better economic viability was recorded for the plants that were transplanted from the improved seedbed. The lower cost of seedbed preparation due to the low time requirement and greater yield due to better seedling vigour compared to that of plants transplanted from conventional seedbeds might be the reason for the greater monetary return.

5 Conclusions

Based on the findings and discussions presented in this study, it can be concluded that during the winter season, when recent temporal variations are not conducive to healthy seedling production, alternative cost-effective techniques should be considered. In this context, the adoption of improved polyethylene-protected seedbed preparation at specific heights is recommended. Enhanced seedbed management not only facilitated robust rice seedling growth under varying climatic conditions but also reduced the duration of the seedling raising period, resulting in economic benefits. Traditional puddled transplanting, known for its labor intensiveness and high water consumption, has several drawbacks. Modified nonpuddled transplanting represents a viable alternative, as evidenced by our experiment where no yield reduction or negative crop growth effects were observed. Furthermore, nonpuddled transplanting resulted in greater monetary returns. Our study also supports intermittent irrigation practices over continuous irrigation, as it enhances water productivity and reduces costs associated with summer rice production. Specifically, transplanting rice seedlings from an improved seedbed to nonpuddled conditions and irrigating at 6-day intervals throughout the growing period proved to be the most profitable and is highly recommended for the eastern Indo-Gangetic Plains.