1 Introduction

Rice is a major crop in Asian countries. Worldwide, it is a staple food for around 50% of total population. In India, it is grown in 43.79 Mha with the production of 112.91 million tonnes and productivity of around 2.58 t/ha [1]. Rice is nutritionally rich in carbohydrate, fibre, protein, vitamin B, iron and manganese. Globally, it serves as a source of energy for more than 50% population. Cultivation of rice in India is done in three seasons. However, rice cultivation during monsoon (Kharif) is highly popular. There are different types of rice cultivation, out of which, transplanted rice cultivation is most prevalent throughout the country. For successful crop establishment and to realise the growth and yield properly, transplanting of rice should be done at right time, with healthy and right aged seedlings under adequate field condition. Proper nursery maintenance as well as main field preparation play a key role for healthy seedlings’ production and their successful transplantation to main field. However, in the present context of climate change, it is often spectacled that either main field is not ready or its condition is not suitable during the ideal time of transplanting of rice seedlings from nursery. This makes the seedlings to remain in nursery for long period resulting high competition among each other for different resources, thereby, poor growth and tiller (or sometimes, entire seedling) mortality [2]. Over aging of rice nursery is a great problem often faced mostly by small and marginal farmers specially during Kharif (June-July to September–October) and Boro (November–December to May–June) seasons.

Climate change arises mainly due to anthropogenic activities. Agriculture is the contributor as well as the victim of the climate change. It has been reported that various forms of energy and other inputs, use of machines, fuel consumption, excessive and unscientific applications of chemical pesticides and fertilizers contribute about 24% of greenhouse gases (GHGs) in the world [3, 4]. Unscientific uses of persistent inputs such as toxic chemical fertilizers, herbicides, insecticides, fungicides and other pesticides etc., deforestation as well as other man-made activities lead to untimely flood, drought etc. as a reflection of climate change [5]. It is a fact that crop cultivation specially rice is suffering and will continue to suffer due to this climate change impacts resulting in demand and supply gap of food for ever increasing population [6]. Under such climate change scenario, double transplanting or sometimes triple transplanting can serve as a contingency approach to establish the rice crop well for realising higher growth and yield of crop by curtailing the risk of crop failure or avoiding the fallowing of the land [7].

Double transplanting makes the seedlings to be transferred to main field from primary nursery via secondary nursery. This process is different from the usual practice of transplanting and generally practiced as contingency approach in situations of heavy rain/flood and delayed onset of monsoon/drought [8]. In lowland areas where inundation is a common phenomenon during monsoon season (up to September), farmers could not transplant during the normal transplanting time and they have to wait until water recedes for transplanting of rice. Further, due to late onset of monsoon or in areas with scarce water availability, farmers are bound to go for late transplanting of rice seedlings. This situation can also arise due to shortage of labour for transplanting process during the peak period of rice seedlings establishment [6]. Sometimes, Boro rice transplanting is also delayed due to late vacation of field by winter crop. Under these situations, double transplanting of long duration photoperiod sensitive rice is an ideal approach to avoid the ill effects of delayed crop establishment as well as over age of the seedlings [9]. Although the information/research on this contingency approach is scanty, an attempt has been made to review this process/methodology, its advantages, role to cope up climate change impacts, research findings as well as some constraints.

2 Double transplanting

Double transplanting (DT) is well suited for establishing rice under delayed onset of monsoon as well as flood like situation where usual transplanting is not possible [10]. Double transplanting (DT) is traditionally practiced in Eastern Uttar Pradesh (Ballia, Gazipur, Mau, Varanasi, Jounpur, Siddharth Nagar, Azamgarh and Chandauli districts), Central Bihar, Chhattisgarh, West Bengal, Meghalaya (Garo hills), Assam, Tamil Nadu, Maharashtra in India, Eastern Nepal and Bangladesh. It is a rice establishment system which is gaining popularity in recent times as one of the promising contingency approaches to mitigate the adverse impacts of climate change. DT is not a new concept. Its reference is found in a sutra of Susruta which mentioned that normal transplanted and successive transplanted (double transplanted) rice cultivation produced highly digestible and nutritious rice grains [11,12,13]. Another literature written by Madanpal Nighantu in 1100 AD indicated high nutritional quality of produce from atiropit/atiraupay (double transplanted) rice [13]. Country wise early documentation on double transplanting has been listed in Table 1. In general, this practice is mostly done in hill agriculture for cultivation of Sali rice (winter rice). However, this can be also suitable in plains. Double transplanting is known by various names across the location such as Ballan in Assam, Changgini geani in N.E. Indian hills like Meghalaya, Kharonha in Bihar, Kalam or Kaiam or Sanda or Sunda in U.P., Bolon system in Bangladesh etc. [14]. This method of crop establishment is highly suitable for Aman (Kharif) rice specially under the situations of heavy rains, flash flood or in flood prone areas (like lowlands of Eastern India) etc. [19]. However, double transplanting is also a well-known practice for Boro rice if during the time of Boro rice establishment, land is occupied by earlier crop due to its late sowing or maturity in winter season. In case of transplanting of overaged seedlings (around 2–2.5 months) from nursery to main field arising from adverse agro-climatic conditions during normal date of transplanting as well as late harvesting of previous crop, seedling mortality, poor establishment rate and less growth are commonly observed due to overcrowding in small nursery area, high competition for various resources among seedlings, pests and disease attacks etc. In such case, DT is highly suitable as a contingency measure to establish overaged rice seedlings. A comparative study between single and double transplanting of rice seedlings has been shown in Table 2. In this system, rice is transplanted twice. Seedlings are raised for around 1 month in medium/high land (primary nursery) due to risk of submergence of seedlings in low land under heavy rainfall situation during kharif season and thereafter, transplanted to secondary nursery having 30% of the total area to be cultivated. After another 30–35 days, seedlings are finally transplanted to main field (low land) [20]. This allows the seedlings to become tall and stout enough to avoid the submergence problem. This method is labour and time consuming but comparatively more economic as the yield of rice under DT is more than the yield of rice from normal transplanting of same aged seedlings [21].

Table 1 Country wise few early documentations on practice of DT method.
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Table 2 A comparison between single and double transplanting methods.
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3 Advantages of double transplanting

DT method provides several advantages over single transplanting of same aged seedlings. Some of these are pointed hereunder.

  • Yield reduction in case of transplanting of overaged rice seedling is a common phenomenon which can be addressed to a high extent through transplanting of rice seedling from primary to secondary nursery. Transplantation shock is associated with rice when seedlings are uprooted from nursery to main field. In DT, this shock is twice. It is well-known fact that the transplanting shock increases with increase of the age of the seedling. In DT, the transplanting shock during transfer of seedlings from primary to secondary nursey is almost similar to that during transfer of young seedlings from nursery to main field. However, in secondary nursery, the seedlings possibly recover at faster rate as the seedlings are properly nourished with adequate nutrients (specially phosphorus) and water. Further, the seedlings are also raised at adequate spacing which creates less intra-competition than the overaged seedlings growing in a single nursery as there since germination to most of their vegetative growth, the seedlings are kept overcrowded. This leads to greater uptake of nutrients and water and storage of food reserve inside the plant under DT method, which help the seedlings to cope up with second transplanting shock quickly than the single transplanted weak/under nourished overaged seedlings. More numbers of effective tillers, filled grains, long and heavy panicles, high test weight etc. due to healthy seedlings make more yield under DT than that of under normal transplanting [6, 24].

  • It helps to produce comparatively healthy, robust and taller rice seedlings which can be suited to heavy rain or flood like situations where normal seedlings face submergence problem [10, 25,26,27,28]. In both the nurseries of DT system, adequate nutrient, water and plant-protection measures are taken. It has been also found that in secondary nursery, seedlings are not overcrowded and grown under very less competition resulting in greater utilization of resources like water, nutrients, sunlight, space etc., which altogether helps the seedlings to become robust and elongate the shoots. This tall seedlings survive flood condition when ordinary seedlings of single nursery get washed away. However, once flood settles down, during final transplanting the leaves/aerial parts are generally clipped down to avoid lodging issue under heavy rain/windy conditions as well as to channelise the food reserve to roots for coping up with transplanting shock. Healthy seedlings lead to high establishment and further growth.

  • DT allows late transplanting of rice seedling to main field in case of heavy rainfall or drought like situation (due to late onset of monsoon).

  • As there is controlled water management, loss of nitrogen is relatively less resulting in efficient utilization of nitrogen [23].

  • During the times of transplanting, diseased or insect affected seedlings are identified and removed resulting in healthy disease or insect free rice plants in main field. Besides, due to robust plants, risks of smut, bacterial blight etc. are comparatively less. Overall, insects and disease infestations are relatively less under DT method than conventional method of transplanting.

  • Due to flexible dates in transplanting, DT can solve the issues of labour unavailability as well as effectively utilizes farm family labours. Further, it generates employment. It solves the issue of high wage rate during the time of normal transplanting of seedlings.

  • DT requires less seeds (35–40 kg/ha) as compared to normal transplanting of overaged seedlings (60 kg/ha) due to less chances of mortality resulting in saving seed cost to an extent.

  • DT helps the crop to mitigate early season drought specially during seedling and vegetative stages through transplanting in secondary nursery under less amount of water. It also requires comparatively a smaller number of life-saving irrigations than normal transplanted rice in drought years resulting in saving of ground water for subsequent crops.

  • DT ensures robust culm with high food reserves. It helps to prevent lodging rice seedlings which is a common phenomenon under low land condition with overaged seedlings [7]. High food reserves also allow the seedlings to survive under adverse climatic conditions.

  • There exists very less competition between seedlings for the resources resulting in attainment of high growth, yield attributes such as less unfilled grains, more effective tillers, longer panicles, high panicle weights etc. and grain yield as compared to conventional transplanting method. In DT method, seedlings are transplanted immediately after uprooting to reduce transplanting shock. Nursery is also well maintained for proper establishment of seedlings by overcoming the root shock and utilizing resources for subsequent growth.

  • Greater root and shoot growth and development of robust seedlings under secondary nursery result in suppression of weeds more under DT over single transplanting method. As there is a chance of root damage during transplanting process, in DT, care is taken to uproot the seedlings with very less disturbance to roots under wet condition, during afternoon hours and soon transplanted to another place properly under flooded condition. Prior to transplanting, leaves are cut down to save the resources/reserves for better utilization in root development through overcoming transplanting shock.

  • Seedling mortality under harsh weather is very common, which can be checked through DT as tall and robust seedlings survive flood or drought more than young seedlings from single transplanting.

  • In DT, wider spacing is adopted than single transplanted primary nursery and adequate aeration through regulating water management practice is ensured resulting in favourable micro-climatic condition for rice growth.

  • Crop experiences early maturity in DT as compared to normal transplanting of same aged seedlings, which allows next crop to be grown on time.

  • In DT system, cost of cultivation is relatively higher due to additional labour involvement for nursery preparation and re-transplanting process as compared to conventional transplanting process. However, this cost can be compensated by high yield as compared to single transplanting of same aged seedlings. Even, sometimes, in spite of high labour cost, overall cost of cultivation under DT is less as there are less weed infestations, insect and disease attacks, less requirement of fertilizer, pesticides, water resulting from well maintenance of seedlings in small land area [29].

  • Tiller mortality and other negative effects of transplanting of overaged seedlings can be avoided as well as under seedling scarcity situation, 8–10 times more land coverage is possible through DT method over single one [10].

4 Considerations for double transplanting

Double transplanting is not suitable for short duration photosensitive rice varieties due to their attainment of reproductive stage after certain period of sowing which is not accepted in this method. Further, in DT system, less plant population can be found for short duration photo-insensitive varieties due to high seedling mortality. Therefore, healthy, certified seeds of long duration (around 145–150 days) photo-insensitive rice varieties are generally recommended for DT. Few rice varieties suitable for DT are listed in Table 3.

Table 3 Recommended rice varieties for double transplanting.
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5 Limitations of double transplanting

Double transplanting method is a traditional contingency approach to avoid yield loss due to late transplanting under adverse weather condition which is increasing in the present climate change scenario. However, this method has some limitations too, which are mentioned below.

  • High labour cost is involved in preparations of main field and two nurseries, uprooting and separating seedlings, transplanting and management practices [10].

  • Straw obtained from rice cultivation through DT method is stiff and not easily palatable to livestock.

  • This system is only useful for small and marginal farmers. For big farmers, it is quite hectic and not possible to transplant large land area two times [23].

  • Only long duration photo-insensitive rice varieties can be used for DT method.

  • Sometimes, tiller mortality (later formed tillers) is observed specifically after transplanting from secondary nursery to main field, making low growth of crop under DT system. Yasmeen et al. [21] noticed lowest number of tillers at post flowering stage due to mortality of later formed tillers.

6 The description of the process of double transplanting

Double transplanting indicates two times transplanting of rice seedlings. At first, seedlings are raised in primary nursery for about 30–35 days maintaining highly dense population (broadcasted @ 25–50 kg seeds sufficient to cover 1 ha of main field). Afterwards, 30–35 days old seedlings are transplanted from primary nursery to secondary nursery (at a spacing of 8–12 cm × 8–12 cm @ 6–12 seedlings/hill) where rice plants grow for another 30–35 days before they are again transplanted to the main field @ 1–3 seedlings/hill at the spacing of 15–20 cm × 10–15 cm [29]. By this time, seedlings become tall (approx. 50–75 cm) and robust to survive the flood or drought situation. Even, the date of re-transplanting is decided when adverse climatic condition i.e., flood or drought is over. In DT, final transplanting to main field is done when continuous heavy rainfall days is over and water level due to flash flood is less and even, if it is high, tall and robust seedlings survive. Further, during drought situation, DT can be successfully done using very less water from rain or irrigation and seedlings can be transplanted to main field when adequate irrigation facilities can be ensured or rainfall occurs later in the season. Sometimes, the arial leaves are partially cut down before establishment to main field. The entire process of double transplanting is shown in Fig. 1. In Assam, primary, secondary nurseries and main field were locally known as Bechan bari, Bolon bari and Dhan bari, respectively [14]. As compared to direct transplanting to main field, a greater number of seedlings (generally, 6–12/hill) are maintained at less spacing of 8–12 cm × 8–12 cm covering 65–70 hills/m2 land area in secondary nursery [2, 21]. In each nursery, nutrient, water managements and plant protection strategies were ensured properly to nurture the seedlings well. Although the nursery management practices are variable across the agro-climatic situations, in primary nursery, FYM/compost@ 1–1.5 t/1000 m2 during last ploughing and N@ 20 kg, P2O5@ 50 kg and K2O@ 50 kg applied prior to sowing and 25–30 kg N is applied at 2–3 leaf stage [30]. In order to ensure high growth by addressing transplanting shock, adequate nutrient management and water management should be followed. In secondary nursery, FYM/compost@ 2–2.5 t, N@ 25–30 kg, P2O5@ 50–60 kg and K2O@ 50–60 kg are applied during land preparation and 25–30 kg N/ha are applied at 15–20 days after transplanting. In both nurseries, assured water supply should be there. During final transplanting, the primary and secondary nurseries are also sparsely covered with seedlings to avoid land wastage.

Fig. 1
figure 1

Double transplanting process in rice

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7 Role of double transplanting as a contingency approach

Double transplanting plays a key role in making the rice plants thick, tall and vigorous which helps to attain greater growth in the main field, early tillering, more no. of tillers/hill, high panicle initiation, greater panicle weight as well as test weight, more filled grains and yield of the crop as compared to same aged seedlings’ single transplanting [29]. Specifically, higher development of shoot and root, more food reserves under DT make the seedlings to be quickly established through better coping up with transplantation shock as compared to single transplanting [10]. Earlier, Singh and Thakur [31], Ziagua [24] and Ghosh [17] also obtained yield advantage of rice under DT method. Ashem et al. [10] observed significantly higher growth, yield attributes and yield of rice as well as economic profitability (Table 4) under double transplanting (30 days+30 days) over normal one of same aged seedlings (60 days). In North Eastern India, double transplanting resulted in increase in yield over single transplanting [6]. The issue of lodging is also relatively less in case of DT resulting in high number of filled grains/panicle than single transplanting [22].

Table 4 Growth, yield attributes, yield and production economics of rice under different planting time, spacing and double and single transplanting methods.
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Rohilla et al. [18] observed in Uttar Pradesh that farmers traditionally practice DT to check lodging problem through reduction of plant height by leaf/shoot clipping during final transplanting to main field, enhance aroma, taste and fluffiness of aromatic rice varieties specially ‘Kalanamak’ in rainfed lowland regions. Ahuja and Ahuja [13] mentioned that this method can be a great option in Haryana, Punjab, Uttar Pradesh and Uttaranchal to grow tall basmati rice by mitigating the lodging issue through arial leaf or shoot cutting during final transplanting to main field. Although the popularity of this method is reduced slightly with the introduction of high yielding dwarf varieties, it is still practiced in many low-lying areas having the issues of flood or inundation. Research works listed in Table 5 indicated its superiority over single transplanting of same aged seedlings in terms of growth, yield and economic profitability.

Table 5 Impact of double transplanting on rice crop and economic profitability
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Verma et al. [29] opined that DT method can avoid the risk of early season drought specifically during seedling and early vegetative stage through growing seedling in small area (secondary nursery) with less water, resulting in water saving. They, further, stated that DT method can save seeds, pesticides and enhance employment and farm income. Satapathy et al. [6] observed higher seedling quality of rice i.e., root length, shoot length and fresh volume of seedlings under DT method over single transplanting. During dry months, DT method can improve cropping intensity through adopting late transplanting which avoids the issue of seedling establishment in later phase of winter season [34]. Kumar et al. [23] compared DT method (first transplanting of 25–34 days old seedlings at close spacing with high number of seedlings/hill in secondary nursery and second transplanting to main field at the seedling’s age of 60–65 days) with Naicha method (single transplanting of young seedlings from seed bed during early season in medium to high lands under less occurrence of submergence due to high rainfall). They noticed early maturity (10 days earlier) of crop, less weed, pest and disease infestations, greater yield, high labour cost, less seed and pesticide costs and profitability under DT method as Naicha method. Earlier, an attempt to standardise the date of transplanting, spacing and seedlings/hill in DT method was made by Thakuria et al. [2], in which maximum growth and yield attributes were observed under transplanting of 3 seedlings/hill on 10th September at spacing of 20 cm × 10 cm (Table 6). As a consequence, grain yield, straw yield, harvest index, net return and B:C were found highest under the same in DT method (Table 6). They highlighted that less inter row competition under 20 cm × 10 cm as well as less disturbance and mortality during separation of tillers as happened under 3 seedlings/hill (primary and secondary tillers were used mostly over tertiary tillers) made the crop to be established well finally in main field from secondary nursery and thereby, resulted in high growth, yield and economic profits. Even, competition between seedlings in secondary nursery is also less to some extent as comparatively higher spacing is maintained over primary nursery as well as nutrients, water and other inputs are provided at desired level. It has been reported that seedlings of one decimal primary nursery area can cover three decimals of area in secondary nursery and these seedlings are enough for occupying 24 decimals area in main field [33]. Yasmeen et al. [21] did not find significant variations in leaf area index, dry matter accumulation at later stages of crop growth and speculated similar photosynthetic rate under various transplanting methods as the reason behind it. However, they observed higher yield attributes and yield under DT method as compared to single transplanting of similar aged seedlings (Table 7). It has been noticed that delay in maturity of kharif rice causes late sowing and harvesting of winter crop, resulting in delay in transplanting of Boro rice in the main field. Khatun et al. [32] reported significant yield reduction of Boro rice when potato was included after harvesting of kharif rice. To address this, double transplanting can be suitable option for Boro rice in medium to high land. DT of Boro rice is an age-old practice along the side of the river of various Asian countries like India, Bangladesh, Nepal etc. Khatun et al. [32] practiced double transplanting in Boro rice (40–45 days at primary nursery followed by transplanting in secondary nursery at spacing of 10 cm ×10 cm with 10–12 seedlings/hill and after another 45 days, transplanting to main field) and observed high growth and yield as compared single transplanting of same aged seedlings.

Table 6 Yield and economics of double transplanted rice grown under various dates of transplanting, spacing and seedlings/hill.
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Table 7 Yield attributes and yield of rice under double and single transplanting methods.
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8 Conclusion

Considering the anthropogenic activities as well as present day agriculture, climate change is an inevitable phenomenon. To tackle this issue and for sustainable crop production in order to feed the enormous population growth, alternative strategies to conventional one is highly needed. Double transplanting, a traditional practice is, therefore, gaining popularity again among the rice growers as this serves as a contingency approach to escape the ill effects of flood arising form heavy rains, drought occurring due to late onset of monsoon, late vacation of field by previous crops, labour shortage during peak period of transplanting, fluctuating water depth, low temperature stress, weed and other pest problems in field etc. Various early documentation as well as research works revealed that this method is well suited over fallowing or single transplanting of similar aged seedlings as it makes rice to grow well and generate high yield and economic return. This method can be accepted when transplanting under ideal time is not possible. However, lack of knowledge or technical know-how, limited land area for nursery preparation, high labour cost etc. often make this method difficult to be used. It has been also noticed that research works on this method is very limited and mostly confined to certain Asian countries. Therefore, adequate research works for standardization of agro-techniques is highly needed. Further, development of suitable varieties and choice of appropriate ones specific to agro-climatic region can make this method highly sustainable. The role of extension service regarding promotion of this technology to new areas is also very important for the rice growers in areas where climate change is a serious issue for crop cultivation.