Traditional methods

Rice-fish integrated farming has been practiced traditionally in many parts of eastern India. Prominent among them are Zabo cultivation in Nagaland, Apatani farming in Arunachal Pradesh, Bhasabandha or Bheri system in Suderbans of West Bengal and Pokkali system in Kerala (Fig. 1). Zabo cultivation (Zabo means impounding runoff water) is majorly practiced by the Chakhesang tribe of Kikruma village in Nagaland. In this agricultural practice, the hill is divided in three-tier: the upper section is reserved as forest area, the middle part of the hill is used for residential purposes and ponds are constructed for rain-water harvesting, and the lower hill area is utilized for rice and fish cultivation. Later, the collected rain water is efficiently utilized for irrigation purposes and as animal drinking water. Cattles are free to gaze in the forest and animal husbandry activities are performed near the ponds, so that animal waste is released in the water which provides nutrients for the paddy cultivation (Nayak et al., Reference Nayak, Nayak, Kumar, Kumar, Panda, Satapathy, Poonam, Mohapatra, Tripathi, Shahid, Chatterjee, Panneerselvam, Mohanty, Sunil and Pathak2020; Amenla and Shuya, Reference Amenla and Shuya2021). The Apatani system, also known as ‘pani-kheti’ or water farming, has been practiced traditionally in the Apatani plateau located in lower Subansiri district of Arunachal Pradesh. In this system, water for irrigation is generally tapped from small streams and channelized to the fields through traditional bamboo and pinewood pipes. Agrarian tribals, especially women are actively engaged in this type of integrated farming. Different strains of carps are simultaneously cultivated with local rice varieties viz. Amo, Mypie and Pyapee. The fry stage of fish, approximately 15–20 mm in size is introduced in the rice fields when rice seedlings are transplanted in the month of April–May. The fish feed on the periphyton that colonize the underwater part of the rice plants and are reared for 3–4 months. The farmers gain an additional earning from a fish production of almost 500 kg/ha in one season (Saikia and Das, Reference Saikia and Das2008). The fish is sold approximately at the rate of INR150/kg (Baruah and Singh, Reference Baruah and Singh2018). Moreover, no chemical fertilizers are added and nitrogen is fixed in the soil by duckweeds Azolla and Lemna. This traditional method has quite a high output and has helped in alleviating poverty in this region. Farmers in this case are estimated to have a 65% higher net income as compared to those practicing rice monoculture (Saikia and Das, Reference Saikia and Das2008). In the estuarine canals and creeks of Sunderbans, West Bengal, prawns and fish are cultivated along with local varieties of rice. Approximately 100–200 kg/ha of fish and prawn are harvested along with 100 kg/ha of rice (Nayak et al., Reference Nayak, Nayak, Kumar, Kumar, Panda, Satapathy, Poonam, Mohapatra, Tripathi, Shahid, Chatterjee, Panneerselvam, Mohanty, Sunil and Pathak2020). In the southern part of India, traditional farming known as Pokkali is practiced in Kerala. In this system, the cultivation of salt-tolerant varieties of rice is alternated with prawn farming in the coastal region. The prawn seedlings feed on the harvested crops, and the rice obtains its nutrients from the waste material excreted by the prawns. Approximately, 70–100 kg/ha rice and 50–200 kg/ha prawns is produced which provides the farmers with considerable income throughout the year (Nayak et al., Reference Nayak, Nayak, Kumar, Kumar, Panda, Satapathy, Poonam, Mohapatra, Tripathi, Shahid, Chatterjee, Panneerselvam, Mohanty, Sunil and Pathak2020).

Modern methods

In India, it is estimated that although 20 million ha of land is suitable for the adoption of integrated rice-fish farming, currently only 0.23 million ha is under rice-fish culture (Mansharamani et al., Reference Mansharamani, Shrivastava and Choubey2020). Hence, to promote integrated rice-fish farming, the Indian Council of Agriculture Research (ICAR) Cuttack, Odisha has developed the following models for the Indian scenario in view of growing population, poverty, and for sustainable environmental conditions (Poonam et al., Reference Poonam, Saha, Nayak, Sinhababu, Sahu, Satapathy, Shahid, Kumar, Jambhulkar, Nedunchezhiyan, Giri, Saurabh, Sangeeta, Nayak and Pathak2019; Nayak et al., Reference Nayak, Nayak, Kumar, Kumar, Panda, Satapathy, Poonam, Mohapatra, Tripathi, Shahid, Chatterjee, Panneerselvam, Mohanty, Sunil and Pathak2020). The modern systems integrate agriculture, horticulture, animal husbandry, aquaculture, and forestry to provide economic stability and better nutrition to farmers without compromising the ecological sustainability.

Crop-livestock-agro-forestry integrated system for lowland rice ecologies

This system includes the cultivation of rice and fish along with poultry, duck farming, and fruit and vegetable production on rain-flooded waterlogged lowland areas. Wide dykes or bunds (2–4 m) covering 20% area are constructed all around the field. Rice is cultivated on 67% of the field and 13% of the area is allocated for pond refuge which is connected on two sides with trenches (Fig. 2). Rice varieties that are high yielding and semi tall such as Sarala, Gayatri, Durga, Varsha Dhan, Naveen etc., are usually preferred. On the dykes, shelter for ducks, goats and poultry are constructed along with bee boxes for apiculture. Various fruit plants including banana, papaya, areca nut and coconut are also planted on the dykes along with seasonal vegetables, mushrooms and different flowers. A variety of fish species with different niches such as surface feeder catla, column feeder rohu and bottom feeder common carp along with giant freshwater prawns in 3:1 ratio are cultured in the trenches. After rice is harvested, the same field is used for the cultivation of various crops including sesame, groundnut, watermelon, sunflower, green gram and vegetables using harvested rainwater. This diversified farming system is validated in Assam with slight modifications in the field design. One hectare of land under this system of cultivation yields 16–18 ton food crops, 0.55 ton of meat, 0.6 ton of fish and prawns and 8000– 12,000 eggs. The production increases significantly by the sixth year of farming (Poonam et al., Reference Poonam, Saha, Nayak, Sinhababu, Sahu, Satapathy, Shahid, Kumar, Jambhulkar, Nedunchezhiyan, Giri, Saurabh, Sangeeta, Nayak and Pathak2019; Nayak et al., Reference Nayak, Nayak, Kumar, Kumar, Panda, Satapathy, Poonam, Mohapatra, Tripathi, Shahid, Chatterjee, Panneerselvam, Mohanty, Sunil and Pathak2020).

Fig. 2.

Schematic representation of crop-livestock-agro-forestry integrated system. In the main field, rice is grown along with the fish cultivation. This is connected to a water refuge pond. On dykes, various agroforestry plants, seasonal fruits and vegetables are grown along with poultry, livestock and duck rearing.

Rice-fish-duck farming system

Nayak et al. (Reference Nayak, Nayak, Panda, Lal, Gautam, Poonam, Shahid, Tripathi, Kumar, Mohapatra and Jambhulkar2018) developed an integrated farming system for medium shallow rain fed lowlands. In this, rice is grown in the main field covering 85% area, a refuge tank is built on the eastern side of the field (10% of the area) with a shelter house for ducks on the refuge tank connected to the raised dykes (0.5–1 m). Fish and duck are introduced in the rice field after twenty days of rice transplantation. Duck varieties such as Indian runner and other indigenous species are stocked at a density of 200 to 250 and allowed to forage in the rice fields. After the harvest of rice, from January to May vegetables and pulses are grown in the main field. This is a mutually symbiotic system wherein all the interacting partners gain considerably. The dropping of the fish and ducks provide organic nutrients to rice, their burrowing activities aerate the soil, and they continually remove pests and weeds. This type of integrated farming system is especially suitable for small and marginal farmers majorly in tribal areas. It provides year long food and employment to the farm families, increases productivity and enhances environmental sustainability. In the rice-fish-duck farming system, 0.7 ton fish, 25,000 eggs, 0.5–0.7 ton of meat and 9–10 ton rice grain are produced annually (Poonam et al., Reference Poonam, Saha, Nayak, Sinhababu, Sahu, Satapathy, Shahid, Kumar, Jambhulkar, Nedunchezhiyan, Giri, Saurabh, Sangeeta, Nayak and Pathak2019; Nayak et al., Reference Nayak, Nayak, Kumar, Kumar, Panda, Satapathy, Poonam, Mohapatra, Tripathi, Shahid, Chatterjee, Panneerselvam, Mohanty, Sunil and Pathak2020).

Rice-fish-azolla-duck farming system

ICAR-National Rice Research Institute has developed a modified rice-fish-duck farming system by introducing azolla, thus minimizing the operational costs (Fig. 3). Azolla is a tropical aquatic fern that grows abundantly in moist soil, shallow ponds and ditches. Along with fixing nitrogen in the soil thus increasing fertility, it also acts as a fodder for livestock. In addition, the azolla increases the dissolved oxygen and creates aerobic conditions. This decreases the population of methanogenic bacteria thereby, reducing the emission of greenhouse gases. The production of 9–10 ton rice grain, 0.6–0.7 ton of meat, 25,000 eggs and 0.7 ton of fish are achieved in the rice-fish-azolla-duck farming system (Poonam et al., Reference Poonam, Saha, Nayak, Sinhababu, Sahu, Satapathy, Shahid, Kumar, Jambhulkar, Nedunchezhiyan, Giri, Saurabh, Sangeeta, Nayak and Pathak2019; Nayak et al., Reference Nayak, Nayak, Kumar, Kumar, Panda, Satapathy, Poonam, Mohapatra, Tripathi, Shahid, Chatterjee, Panneerselvam, Mohanty, Sunil and Pathak2020). It has been reported that rice-fish-azolla farming system generated an additional income of INR 8817/ha and INR 3219/ha over rice monoculture and rice-fish culture, respectively (Singh et al., Reference Singh, Singh, Supriya and Singh2018).

Fig. 3.

Schematic representation of rice-fish-duck-azolla farming. Azoolla is allowed to grow in the main rice field along with fish and duck rearing.

The field is divided into four tiers in this farming system for the cultivation of rice, fish, fruits, and vegetables (Fig. 4). The design of the field includes two upland areas viz. tier I and tier II which covers 15% area of the field. Perennial and seasonal fruit crops such as pineapple, banana, papaya, guava, mango, etc. are grown in tier I, whereas, vegetables and tuber crops including greater yam, elephant foot yam, sweet potato and yam bean are cultivated in tier II. Rice is grown on tier III (20% of the area) that is lowland rainfed area with depth of upto 50 cm and on tier IV (20% of total land area) which is deep water area, 50–100 cm in depth. The rice field is connected to a refuge pond for growing fish and freshwater giant prawns. There are raised dykes or bunds all around covering 25% of total land area. There is a small pond for rearing fish fingerlings. During wet season, different varieties of rice with high yield are grown on lowland water-fed area (Sarla, Gayatri, Pooja) and deep-water area (CR Dhan 508, CR Dhan 505, CR Dhan 500, Jayanti Dhan, Varshadhan) along with the culture of fish and prawn. In the dry season, rainwater harvested in the refuge pond is used for the cultivation of sunflower, sweet potato, ground nut and vegetables on tier III and dry season rice on tier IV after harvesting rice grown in wet season. On the dykes, agro-forestry and plantation crops, are grown and poultry and duck houses are built. One hectare of this kind of multi-tier rice-fish-horticulture-agroforestry based system can annually produce approximately 14–15 ton of food crop, 1 ton of fish and prawns, 0.5–0.8 ton of meat, 10,000 to 12,000 eggs and 3–5 ton animal feed. The productivity of food crops increases substantially after the 8th year, once the perennial trees start producing fruits (Poonam et al., Reference Poonam, Saha, Nayak, Sinhababu, Sahu, Satapathy, Shahid, Kumar, Jambhulkar, Nedunchezhiyan, Giri, Saurabh, Sangeeta, Nayak and Pathak2019; Nayak et al., Reference Nayak, Nayak, Kumar, Kumar, Panda, Satapathy, Poonam, Mohapatra, Tripathi, Shahid, Chatterjee, Panneerselvam, Mohanty, Sunil and Pathak2020).

Fig. 4.

Schematic representation of multi-tier rice-fish-horticulture-agro-forestry-based farming system. On tier I and II, fruit and vegetables crops are grown and rice-fields are present on tier III and IV. The dykes are used for poultry farming and agroforestry. There is a refuge pond for growing fish and freshwater prawns which is connected to the rice fields. There is also a small pond for rearing fish fingerlings.

Rice- ornamental fish culture

There is a growing market for ornamental fish in India and ornamental fish export has shown an exponential increase over the years (Rani et al., Reference Rani, Immanuel and Ranjan2014). However, at present the production does not meet the demand. Rice-ornamental fish culture is similar to the basic rice-fish cultivation practice in which edible fish is replaced by ornamental fish such as gouramies, guppies, gold fish, carps, zebrafish etc. In this, well-irrigated rice fields having clayey soil with greater water retention capability is preferred. A water refuge covering 15% of the total field is constructed at one end of the field and before introducing the fish, cow dung slurry along with nitrogen-phosphorous-potassium (NPK) fertilizers are added to promote the growth of planktons. The fish feed on planktons and are also provided with commercial feed. Besides, fish also feed on pests and insects including mosquito larvae infesting the rice fields. High yielding and semi-dwarf varieties of rice such as Naveen, IR 64, IR 36 and Lalat are suitable for areas under irrigation during summer season, however rice varieties such as Varsha Dhan, Sarala, Gayatri and Durga are cultivated in medium deep lowlands during the wet season. These rice varieties have in-built tolerance to the diseases and pests. The equal number of male and female ornamental fish are reared in the rice field. The juveniles are cultured in rice fields for a duration of two to six months depending on the species of ornamental fish till the adult size is obtained. In this integrated farming system approximately 25,000-6 lakh ornamental fish can be produced along with rice yield up to 3–5 ton/ha of the field (Poonam et al., Reference Poonam, Saha, Nayak, Sinhababu, Sahu, Satapathy, Shahid, Kumar, Jambhulkar, Nedunchezhiyan, Giri, Saurabh, Sangeeta, Nayak and Pathak2019; Nayak et al., Reference Nayak, Nayak, Kumar, Kumar, Panda, Satapathy, Poonam, Mohapatra, Tripathi, Shahid, Chatterjee, Panneerselvam, Mohanty, Sunil and Pathak2020). The ornamental fish are sold at INR 10–30 per fish (Shinoj et al., Reference Shinoj, Baiju and Vijayagopal2021).

Rice-based farming system under irrigation condition

In the irrigated lowland area, a farm of one acre size is divided into two rice-fish fields covering 30% area, each connected with refuge occupying 15% area and 30% area is allotted as fish nursery ponds for culture of fish fingerlings. In the remaining area, dykes are built around the farm on which agro-forestry plants (neem, bamboo, aonla, teak and sisoo), horticulture crops (pineapple, areca nut, spices, papaya, lemon, litchi, mango and banana), flowers (jasmine and marigold), and different seasonal vegetables are grown. Small duck houses and poultry units are constructed on the dykes for bird rearing. Different seasonal varieties of rice are cultivated throughout the year including summer rice (Sidhant, Vandana) followed by the kharif rice (Varshadhan, CR Dhan 505) and then rabi rice (High protein rice, Naveen) along with fish species such as mrigal, catla and rohu. This system results in the production of 0.8–1.0 ton rice, 0.1 ton fish, 0.05 ton meat, 1.4 ton vegetables and 0.09 ton fruits (Poonam et al., Reference Poonam, Saha, Nayak, Sinhababu, Sahu, Satapathy, Shahid, Kumar, Jambhulkar, Nedunchezhiyan, Giri, Saurabh, Sangeeta, Nayak and Pathak2019; Nayak et al., Reference Nayak, Nayak, Kumar, Kumar, Panda, Satapathy, Poonam, Mohapatra, Tripathi, Shahid, Chatterjee, Panneerselvam, Mohanty, Sunil and Pathak2020).

Food diversity and productivity

Through the integration of rice-fish farming, the productivity of food using the same land and water resources can be substantially increased as compared to rice monoculture. More than 1000 kg/ha fish production can be achieved in medium rainfed paddy fields within four months (Mohanty et al., Reference Mohanty, Verma and Brahmanand2004). Mishra et al. (Reference Mishra, James, Mohanty and Anand2014) estimated that more than 1600 kg/ha fish can be produced within six months in rainfed rice-fish farms of Eastern India. Moreover, the fish as well as rice productivity can be increased substantially by stocking yearling instead of fry as demonstrated by Dey et al. (Reference Dey, Sarma, Kumar, Mohanty and Kumar2019). The fish in paddy fields increases soil fertility and dissolved oxygen levels in water and feeds on the pests and aquatic weeds, controls the growth of planktons and bacteria, thereby resulting into 8–25% enhancement in rice production under the rice-fish farming system (Mishra and Mohanty, Reference Mishra and Mohanty2004; Mohanty et al., Reference Mohanty, Jena, Thakur and Patil2009). Recently, Dey et al. (Reference Dey, Sarma, Kumar, Mohanty and Kumar2019) reported an increase of 6.73% and 4.36% of paddy straw and grain per hectare, respectively, in rice-fish farming compared to rice monoculture in Bihar. The productivity of rice could be further enhanced in the rice-fish farming system by use of inorganic nitrogen fertilizers as shown in a field experiment conducted by Water Technology Center for Eastern Region (ICAR), Bhubaneswar (Brahmanand et al., Reference Brahmanand, Ghosh and Sahoo2009). Not surprisingly, Ahmed and Turchini (Reference Ahmed and Turchini2021) asserted that annual production of fish and rice could be increased by 27% with the adoption of rice-fish cultivation in 50% rice fields globally available. Further, the integration of poultry, duck farming, horticulture and agro-forestry with rice-fish farming for eggs, meat, vegetables and fruits production results in the diversity of food supplies (Poonam et al., Reference Poonam, Saha, Nayak, Sinhababu, Sahu, Satapathy, Shahid, Kumar, Jambhulkar, Nedunchezhiyan, Giri, Saurabh, Sangeeta, Nayak and Pathak2019). Therefore, adoption of rice-fish farming addresses key objectives including enhancement in food diversity and productivity with efficient utilization of resources and maintenance of sustainable environment (Ahmed and Garnett, Reference Ahmed and Garnett2011; Poonam et al., Reference Poonam, Saha, Nayak, Sinhababu, Sahu, Satapathy, Shahid, Kumar, Jambhulkar, Nedunchezhiyan, Giri, Saurabh, Sangeeta, Nayak and Pathak2019).

Socio-economic stability

For the overall development of a country, the development of each individual, both socially and economically is required. In a developing country like India, where a major portion of the population depends on agriculture and its allied sector for their source of income, the development of the agriculture sector would translate into improved profit and enhance employment opportunities for vulnerable farmers. In a study in Karnataka, it was observed that an additional employment of 41.4% was generated in integrated rice-fish culture and labor use efficiency was also higher as compared to rice monoculture (Channabasavanna and Biradar, Reference Channabasavanna and Biradar2007). Rautaray et al. (Reference Rautaray, Dash and Sinhababu2005) demonstrated that a net profit of INR 11,226 was obtained from 5000 m² as compared to INR 4000–6248 generated from conventional rice monoculture in rainfed lowland of Assam. The net income of farmers increased further (INR 1,55,920/ha in first season and INR 2,28,090/ha in second season) in case of rice-fish-poultry culture and the post harvest soil nutrient (N, P, and K) was also quite high when compared to rice monoculture or rice-fish culture (Murugan and Kathiresan, Reference Murugan and Kathiresan2005). Thus, with the adoption of integrated rice-fish farming, the income of farmers increased significantly, which stabilizes the economic and social state of the poor (Channabasavanna et al., Reference Channabasavanna, Biradar, Prabhudev and Hegde2009; Datta et al., Reference Datta, Nayak, Sinhababu and Adhya2009; Ahmed and Garnett, Reference Ahmed and Garnett2011) (Table 1). Although a comprehensive socio-economic study has not been conducted in India, reports from other south Aaian countries such as Bangladesh and Vietnam indicate more socio-economic stability among farmers practicing integrated rice-fish culture (Frei and Becker, Reference Frei and Becker2005).

Table 1.

Benefit-cost ratio of different rice-fish integrated farming models compared with rice monoculture

The benefit-cost ratio is calculated by dividing the total output (net gain) with the initial investment (cultivation cost). The value of the benefit-cost ratio equals one depicts neither profit nor loss, value greater than one indicates profit, and value less than one shows net loss.

In addition to being staple food, rice and fish are nutritious food and contribute to the health of the farmers. Fish is rich in proteins, vitamins, micronutrients and fatty acids. The integration of duck, cattle, poultry and horticulture in rice-fish farms provides nutritious food items such as eggs, meat, milk, curd and seasonal vegetables with an increase in the income of farmers (Nayak et al., Reference Nayak, Nayak, Panda, Lal, Gautam, Poonam, Shahid, Tripathi, Kumar, Mohapatra and Jambhulkar2018; Poonam et al., Reference Poonam, Saha, Nayak, Sinhababu, Sahu, Satapathy, Shahid, Kumar, Jambhulkar, Nedunchezhiyan, Giri, Saurabh, Sangeeta, Nayak and Pathak2019). After rice cultivation, waste such as rice straw and husk can be used for household purposes including electricity production, fodder for cattle, constructing roofs and as energy source for cooking food. Thus, rice-fish co-cultivation not only provides opportunities for the livelihood but also strengthens social status and engages in empowering women by providing employment opportunities.

Sustainable environmental conditions

Unregulated agriculture practices and intensive food production presents a major threat to the environment. Integration of rice-fish cultivation is an approach toward sustainable agriculture methods. Fish behavior in rice fields helps in achieving multiple objectives, including maintaining dissolved oxygen levels in water, reduction in weeds and pests abundance, enriching soil fertility, penetration of sunlight and nutrient recycling (Halwart and Gupta, Reference Halwart and Gupta2004; Nayak et al., Reference Nayak, Nayak, Panda, Lal, Gautam, Poonam, Shahid, Tripathi, Kumar, Mohapatra and Jambhulkar2018; Wan et al., Reference Wan, Li, Li, Cavalieri, Weiner, Zheng, Ji, Zhang, Zhang, Zhang, Bai, Chen, Zhang, Tao, Zhang, Lv, Jiang and Li2019). The study conducted by Nayak et al. (Reference Nayak, Nayak, Kumar, Kumar, Panda, Satapathy, Poonam, Mohapatra, Tripathi, Shahid, Chatterjee, Panneerselvam, Mohanty, Sunil and Pathak2020) and Poonam et al. (Reference Poonam, Saha, Nayak, Sinhababu, Sahu, Satapathy, Shahid, Kumar, Jambhulkar, Nedunchezhiyan, Giri, Saurabh, Sangeeta, Nayak and Pathak2019) have shown a significant decrease in pests and increase in weed control efficiency in rice-fish culture and rice-fish-duck culture when compared to rice monoculture. Among fishes, the weed control efficiency of grass carp was found to be highest (63%) followed by silver barb (61%) and common carp (47%). Among Indian carps, only rohu was able to reduce the weed biomass and showed weed control efficiency of 23% (Sinhababu et al., Reference Sinhababu, Saha and Sahu2013). Many fishes play an important role in biocontrol of rice pests such as stem borers, snails, hoppers, gall midge etc. Prominent among them are common carp, magur, koi and colisa that feed on rice pests (Poonam et al., Reference Poonam, Saha, Nayak, Sinhababu, Sahu, Satapathy, Shahid, Kumar, Jambhulkar, Nedunchezhiyan, Giri, Saurabh, Sangeeta, Nayak and Pathak2019).

The phytoplankton and zooplankton in rice field are good source of food for fish (Nayak et al., Reference Nayak, Nayak, Panda, Lal, Gautam, Poonam, Shahid, Tripathi, Kumar, Mohapatra and Jambhulkar2018) and their consumption by fish results in protection against disease outbreak (Matteson, Reference Matteson2000), and reduction in intensive use of pesticides (Xie et al., Reference Xie, Hu, Tang, Wu, Li, Yuan, Yang, Zhang, Luo and Chen2011). The fecal matter of fish contains phosphorous and nitrogen which improves soil fertility, nutrient recycling (Nayak et al., Reference Nayak, Nayak, Panda, Lal, Gautam, Poonam, Shahid, Tripathi, Kumar, Mohapatra and Jambhulkar2018) and reduction in fertilizers application (Xie et al., Reference Xie, Hu, Tang, Wu, Li, Yuan, Yang, Zhang, Luo and Chen2011). When livestock is introduced in rice-fish coculture, livestock manure and the dropping of duck and poultry are added to the field at different times that enhances the organic content of the field and thus the sustainability of the model system. In addition, rice-fish co-cultivation helps in the reduction of N₂O greenhouse gases emission upto 9% compared to rice monoculture. However, the emission of methane from rice-fish farming is comparatively higher, but by combining the appropriate fish with rice cultivation this drawback can be less harmful for the environment (Datta et al., Reference Datta, Nayak, Sinhababu and Adhya2009; Bhattacharyya et al., Reference Bhattacharyya, Sinhababu, Roy, Dash, Sahu, Dandapat, Neogi and Mohanty2013).