Traditional grain storage methods: An exploration of their contribution to the sustainability of Indian agriculture

Abstract Despite having a wide variety of traditional grain storage structures that serve to store up to 70% of the total amount of grains produced, India loses more than 14 million tonnes of food grain in storage every year. In light of this, it is necessary to conduct a detailed mapping and analysis of these structures, focusing on their mode of operation, advantages, drawbacks, and ways to improve them. A narrative review approach was used to search, screen, and analyze the articles incorporated in this review. Several scientific databases, including Scopus and Google Scholar, were searched to find relevant articles. The study’s findings indicate that these storage structures are comparatively inexpensive, eco-friendly, and easily accessible to farmers. Moreover, they have been created using traditional knowledge, values, and locally sourced materials, thereby promoting agricultural sustainability. However, most of them have limited storage capacity and are vulnerable to significant grain losses because they cannot provide complete protection against moisture, insects, rodents, fungus, and other harmful microorganisms. It is possible, however, to improve the storage capacity and efficiency of these structures by modifying them slightly using modern materials and scientific knowledge.


Introduction
Postharvest food loss is arguably one of the most critical challenges for the sustainability of agriculture in developing countries (Ali et al., 2021;Bisheko & Rejikumar, 2023).Agricultural sustainability refers to the production of safe and high-quality farm produce while safeguarding and enhancing the natural environment, livelihoods, and the general well-being of farmers and their laborers, as well as the local community at large (Kareemulla et al., 2017).
Postharvest food loss negatively impacts society, the economy, and the environment.Environmental effects of post-harvest loss include greenhouse gas (GHG) emissions and the waste of natural resources used in crop production, such as water, energy, and land (Ali et al., 2021).Among the negative social and economic impacts of postharvest loss are the exacerbation of food insecurity, nutritional insecurity, and the impoverishment of poor farmers (FAO, 2019;Habanyati et al., 2022).For instance, the situation is very alarming in Africa as more than 246 million people go to sleep hungry each night, which is almost 20% of the population (Food and Agriculture Organization, 2017).According to FAO (2019), the number of undernourished people in Sub-Saharan Africa reached a record high of 234 million, higher than any other region.Likewise, nearly 190 million people in India go to bed hungry every day (Food and Agriculture Organization, 2017).
Postharvest loss includes food loss along the entire food supply chain, from the time a crop is harvested until it is consumed (Bisheko & Rejikumar, 2023).The losses can fall into several categories, including weight loss from deterioration, loss of nutrients and seed viability, quality loss, and commercial loss (Kumar & Kalita, 2017).The extent of postharvest losses along the food supply chain varies significantly depending on the type of crop, geographical area, farmer income groups, etc (Kumar & Kalita, 2017).Despite that, as the crops pass through the various stages of the food supply chain, such as harvesting, handling, storing, processing, transportation, marketing, etc., losses frequently occur.It has been observed that developing and developed countries exhibit quite different patterns of food loss and waste (Bisheko & Rejikumar, 2023).In developing countries, large amounts of food losses occur during the postharvest and processing stages (Bisheko & Rejikumar, 2023).This can be mainly attributed to poor post-harvest infrastructure and inefficient postharvest practices (Bisheko & Rejikumar, 2023).Manandhar et al. (2018) estimate that around $310 billion worth of food is spoiled and wasted annually in developing countries, with about 65% of those losses occurring during the stages of production, processing, and postharvest.On the contrary, in developed countries, more food losses occur at retail and consumer stages as opposed to those from postharvest operations, commonly referred to as "food waste," (Bisheko & Rejikumar, 2023).This can be mainly attributed to the adoption of efficient farming and postharvest practices that promote effective food distribution (Hodges et al., 2011).According to Hodges et al. (2011), consumers in Europe and North America waste around 95-115 kg of food per person annually, compared to 6-11 kg in South/Southeast Asia and sub-Saharan Africa.Among various crop groups, Hodges et al. (2011) reported that on a weight basis, cereal crops, roots crops, and fruit and vegetables account for roughly 19%, 20%, and 44% of losses, respectively.In terms of calorific content, losses in cereal crops account for the highest share (53%) (Kumar & Kalita, 2017).Food crops such as rice, maize, and wheat are the most popular food crops around the globe and are the major source of staple cereals in many developing countries (Kumar & Kalita, 2017;Manandhar et al., 2018).Minimizing cereal losses along the supply chain could therefore be a sustainable solution to increase food availability and enhance farmers' livelihoods without putting any additional pressure on natural resources (Bisheko & Rejikumar, 2023;Kumar & Kalita, 2017).
While grain losses occur throughout the supply chain, the highest amount in developing countries occurs during the storage phase (Kumar & Kalita, 2017;Manandhar et al., 2018).For instance, out of the approximately 315.7 million tonnes of food grain produced in India each year, nearly 14 million tonnes, worth over Rs. 7,000 crores are lost during storage (NAAS, 2019;Sahu et al., 2015).A variety of factors can lead to grain losses, including the nature of the storage facility, duration, how grains are stored, etc (Basavaraja et al., 2007;Nagpal & Kumar, 2012;Sharon et al., 2014).Environmental factors like temperature, grains' moisture content, pH, etc., as well as biological agents like fungi, bacteria, pests, etc., can also contribute to storage losses (Nagpal & Kumar, 2012).However, despite being a tremendous challenge, storage losses can be minimized through the use of efficient grain storage structures and improved practices, contributing to the sustainability of agriculture (Kumar & Kalita, 2017;Manandhar et al., 2018;Mobolade et al., 2019;Prakash et al., 2016;Shukla et al., 2019).
Traditional storage techniques were mainly used in ancient times and are still used up to now in developing countries (Kumar & Kalita, 2017;Manandhar et al., 2018).For instance, it is estimated that around 60-70% of the total food grains produced in India are stored in traditional storage structures (e.g., Gourds, Sanduka, Kanaja, Kothi, Hagevu, Earthen pots, Gunny bags, etc.), especially in rural areas (Kumar & Kalita, 2017;Manandhar et al., 2018;Mann et al., 2016).Farmers in West Africa store their grains indoors, in open areas, in baskets, jute or polypropylene bags, raised platforms, conical structures, and clay structures (Mobolade et al., 2019).Farming communities in East and Southern Africa store their crops in jute or polypropylene bags with ashes generated from cow dung, in traditional cribs, metal bins, pits, roofed iron drums covered with mud, etc (Manandhar et al., 2018;Mobolade et al., 2019).
Despite having a wide variety of traditional grain storage structures, India suffers substantial grain storage losses of more than 14 million tonnes every year.As these indigenous storage structures serve to store up to 70% of the total food grains produced in the country, the enormous amount of grain losses recorded in the country indicate significant gaps in their storage efficiency.Considering the criticality of this situation to the sustainability of agriculture, it becomes necessary for these traditional structures to be optimized.Achieving this, however, requires comprehensive information about these traditional storage structures, which can better inform the kind of modifications and technologies needed to be applied.However, this type of information is very scarce in the body of literature on indigenous methods of grain storage despite the efforts of various authors to investigate the indigenous grain storage structures and practices used by farmers in different parts of India.
In light of the above observations, this study aims to provide a thorough review of the literature on the traditional grain storage structures and methods in India with a focus on their mode of operation, benefits, and drawbacks, as well as potential improvements that could be made in the future for sustainability.
This study is crucial for preserving the gradually eroding traditional practices and the indigenous knowledge on protecting stored grain for a sustainable future, especially in small-scale farming systems in developing nations.Despite this, this study also serves as a platform for the exchange of traditional knowledge, allowing extension workers and farmers from other developing countries to study and adopt India's traditional grain storage structures and methods depending on their needs.Furthermore, information such as this is essential to postharvest specialists, historians, stored product entomologists, policymakers, and all other parties involved in stored grain protection.

Materials and methods
This paper was guided by the following three primary research questions: (i) What traditional methods of grain storage are employed by India's marginal and smallholder farmers?(ii) What are the major advantages and drawbacks of these traditional grain storage methods?(iii) How do these traditional grain storage methods help India achieve its sustainable development goals and engage in environmentally friendly agriculture?To answer these questions, a narrative literature review approach is applied.This kind of review seeks to provide a critical viewpoint on a number of the most essential narratives in the literature, as well as an intellectual overview, explanation, and critique, to help readers gain a broader understanding of the history and current status of traditional methods of grain storage in India (Ferrari, 2015).

Strategy for literature search and criteria for inclusion/exclusion
A systematic step-by-step approach was used to search, screen, and analyze the papers included in this narrative review (Ferrari, 2015).In an effort to reflect a wide, diversified, and unbiased set of articles, a systematic database search of keywords and a screening process were conducted to find relevant papers for the review (instead of cherry-picking articles based on a list of alreadyidentified papers,).

Database and keywords utilized
The identification of relevant studies to be included in our study was mainly based on keyword searches in journal databases, specifically Scopus and Google Scholar, as well as the backward search of relevant papers.The two databases Scopus and Google Scholar were selected as this combination was thought to capture a wide range of literature on India's traditional grain storage systems while minimizing duplication.The keywords were mostly derived from previously published studies (Kumar & Kalita, 2017;Mann et al., 2016;Nagpal & Kumar, 2012).Upon reviewing a few published studies, we noticed that some terms related to indigenous storage structures and methods are interchangeable.As a result, several keywords were combined (at least eight keywords) to retrieve a substantial number of relevant papers from the electronic databases.In keeping with the primary purpose of this study, "exploring the contribution of traditional grain storage structures and methods to the sustainability of Indian agriculture", we added two additional keywords: agriculture or farming communities or farmers, and India.The collection of keywords used to search for articles in electronic databases is presented in Supplementary material Appendix 1, Table A1.

The Inclusion and exclusion criteria
The relevant papers for the narrative review were selected using a variety of inclusion and exclusion criteria (see Supplementary material Appendix 2, Table A2).First, in terms of the literature type, the review process only took into account journal-based research publications.Another criterion is based on the language of the publication, for instance, papers that were not published in English were excluded.Given that traditional storage structures and methods have been in use for decades, as well as the fact that the attention on post-harvest research began to grow in the 1990s (Kitinoja et al., 2011), and increased significantly over the last two decades (Baributsa et al., 2014;Moussa et al., 2011), our study considered journal papers that were published between 1990 and 2023.The fourth criterion is related to geographical location, for instance, the studies that did not take place in India were excluded.After this, we carefully went through the title, abstract and full text of each paper, and included the ones which examine the traditional grain storage methods used by Indian farmers.

Literature selection process
After we had searched for articles using the keyword listed in Table 1, a total of 200 papers were retrieved (33 papers from Scopus and 167 papers from Google Scholar.A total of 21 manuscripts were duplicates; hence they were eliminated from the entire pool.The second They are mostly limited to smallscale grain storage.
They can be produced in huge quantities, packed in a variety of sizes, and used for smallscale and bulk storage of grains.
( Karthikeyan et al., 2009;Kiruba et al., 2006;Kumar & Kalita, 2017;Mobolade et al., 2019;Prakash et al., 2016;Somavat et al., 2017) Gourds (Figure 6A) Gourds are produced from the tough dried outer shell of the fruit belonging to the squash or Cucurbitaceae class, which is native to tropical and subtropical regions.They are usually kept inside the house, especially in areas where they would not be easily infested with insects or exposed to moisture. Chhattisgarh.
They are inexpensive, protect grains effectively, and allow farmers to easily track insect invasions.
Their storage capacity is limited to 5 to 30 kg.
Increase their size to enhance their capacity to hold more grains.They are situated above the ground, allowing for easy grain monitoring while protecting the grains from soil moisture.They are not ideal for preserving grains for lengthy periods.

Making them fully hermetic by adding
an extra coating on their outer surfaces using readily available materials such as varnish, dry oil or pure cement will boost their ability to store grains for a long period of time.(Gaur, 2016;Mann et al., 2016;Prakash et al., 2016) (Continued) stage involves the screening process.At this point, we excluded 96 papers based on our inclusion and exclusion criteria (such as articles that are not research articles, are not reported in English, were published before 1990, and were based outside of India).As a result, about 83 articles were selected to move on to the third stage, namely eligibility.At that point, we carefully reviewed the title and abstract of each paper and rejected 34 papers if the following words did not appear in the title and/or abstract; traditional grain storage methods, traditional grain storage practices, indigenous grain storage structures, and farming communities or farmers.A total of 49 articles were reviewed in the fourth phase, whereby a total of 11 papers were excluded as they did not examine the traditional grain storage methods used by Indian farmers.Five additional papers were added based on reference checking of retrieved papers.As a result, a total of 43 papers were selected for the final review process (see Figure 1).Source: Author's own.

Data extraction and synthesis
The analysis was carried out in two steps.The first step in our analysis was to classify and count papers based on crucial details such as the study's region in India, the year of publication, and the type of grain examined.The second stage of the study involved a detailed narrative analysis of the traditional grain structures and practices across the Indian grain supply chain, with a special focus on storage.

Description of the included studies
This section gives a description of the 43 shortlisted articles involved in the review, providing context for the analysis offered in sections 2 and 4.

Year of publication
Within the article publication time limit set for this review (1990 to 2022), as shown in Table 2, the number of articles published in this domain peaked in 2013 and sharply declined in 2014, 2018, and, Source: Author's own.Source: Author's own.
especially in 2022 where no single study was found (see Figure 2).The trend is indicative of the dwindling attention scientists and research institutions are paying to this area of research.

Study's location in India
A large number of articles focus on the whole of India (n = 21) followed by Karnataka (n = 5), Tamil Nadu (n = 3), and Madhya Pradesh (n = 2).Other states, including Assam, Bhubaneswar, Chhattisgarh, Gujarat, Odisha, Uttarakhand, Punjab, and West Bengal had just one study each (see Figure 3).This pattern highlights the dearth of state-wise information regarding these traditional grain storage facilities.

The type of grain crop studied
Most articles are about general food grains (29), rice (4), rice and wheat (4), wheat (2), and millet (2), while rice and red gram, as well as wheat and mustard, contain only one study each (see Figure 4).This trend indicates the paucity of studies on crop-specific traditional grain storage structures and methods.Future research targeting the traditional interventions for post-harvest grain loss reduction could fruitfully explore this area in more depth.

Results and discussion
The food grain supply chain comprises various important processes such as harvesting, threshing, winnowing, cleaning, drying, storing, processing, and transportation to facilitate grain distribution from farm to consumer (Grover & Singh, 2013;Kumar & Kalita, 2017;Sahu et al., 2015).The supply chain for agricultural products experiences quantity losses owing to a variety of factors, including inappropriate handling, insufficient facilities for processing, decomposition, and damage caused by pathogens, pests, etc (Grover & Singh, 2013;Sahu et al., 2015).According to many authors, losses in storage operations are the most substantial among all stages of the grain supply chain in India (NAAS, 2019;Sahu et al., 2015).The following sections summarize various stages involved in India's grain supply chain and present a description of traditional structures and facilities used at each stage, their benefits and drawbacks, and how such practices contribute to sustainability.

Harvesting
Harvesting is the initial step in the grain supply chain and is integral to the overall quality of the crop (Kumar & Kalita, 2017).Harvesting must be done at the right time to preserve grain quality and minimize losses, ideally when the crop is at its optimum maturity and moisture level (Kumar & Kalita, 2017;Manandhar et al., 2018).Grains that are not fully matured contain more moisture and more enzyme activities, hence they tend to degrade much faster than their fully matured counterparts.Additionally, they will require longer drying times or may create optimal conditions for microbial contamination, Source: Author's own.leading to higher drying costs or losses (Kumar & Kalita, 2017;Manandhar et al., 2018).However, when crops mature and are not harvested on time, they become susceptible to attack by rodents, hazardous pests, and fungi, and they may also deteriorate owing to damp conditions caused by rainfalls, morning dew, or other natural disasters while in the field (Kumar & Kalita, 2017;Manandhar et al., 2018).A study conducted in Karnataka, India found that delayed harvesting caused paddy harvesting losses to rise by 10.3% (from 1.74% to 1.92%) (Kannan et al., 2013) Grain crops are typically harvested manually in India, using simple equipment such as a sickle or knife (Karthikeyan et al., 2009;Mishra & Satapathy, 2021;Patel et al., 2015).Harvesting operations can also be carried out mechanically by Indian farmers using combine harvesters available mostly on a hiring basis in various states (Patel et al., 2015).The combine harvesters offer a variety of options, including reaping, threshing, and winnowing, in addition to covering a large area within a short timeframe (Patel et al., 2015).However, despite the introduction of combine harvesters for grain crop harvesting in India, over 90% of the cultivated area is still harvested with sickles (Patel et al., 2015).
The curved design of sickles enables the simple gathering of harvested grains in addition to making harvesting of crop ear heads, branches, or even entire plants easier, making it far better than other tools (Karthikeyan et al., 2009).The knife is also quite simple and convenient, making harvesting considerably easier (Karthikeyan et al., 2009).Apart from their efficiency and ease of use, sickles and knives are affordable, making them easily accessible to many smallholder farmers (Mishra & Satapathy, 2021).Harvesting with these hand tools, however, is time-consuming, and labor-intensive, and it wastes a significant amount of grain due to shattering and scattering (Kumar & Kalita, 2017;Mishra & Satapathy, 2021).According to a study carried out in Punjab, India, wheat harvesting losses soared by 67% from 1,5% to 2,5% due to substantial shattering losses induced by delayed harvesting (Grover & Singh, 2013).Moreover, when the farm expands in size, employing these hand tools becomes difficult and ineffective, necessitating the adoption of mechanized harvesting equipment instead (Mishra & Satapathy, 2021).

Threshing
The primary goal of the threshing procedure is to separate the grain kernel from the plant.Rubbing, peeling, impact action or a blend of these operations is used to complete the process (Kumar & Kalita, 2017).Manual labor, animal power, or mechanical threshers can all be used to complete the task.Typically, threshing takes place in the field or on a designated floor or ground.Manual threshing is the most popular method in India, which entails trampling the grains under the feet of animals or tractor wheels, smashing the grains with sticks, or manually hitting the stacks of crop stems on wooden poles and separating grains by stroking them against stones or wooden rollers on the hard surface (Kumar et al., 2013;Mishra & Satapathy, 2019;Singh et al., 2015).These manual threshing methods are relatively affordable and readily available to farmers (Mishra & Satapathy, 2019).However, these methods are characterized by low productivity and slowness, as well as being impracticable when dealing with large volumes of yields and entail a great deal of human drudgery (Kumar & Kalita, 2017).Additionally, they are subject to high operating costs due to limited output, as well as significant grain losses due to spills, grain cracking caused by excessive pounding, unthreshed grains, attacks by rodents, birds, and other hazardous pests, as well as unexpected downpours and fire incidents (Kumar & Kalita, 2017;Sarkar et al., 2013).
Threshers are popularly utilized in India in place of traditional threshing methods, and they provide a number of benefits in comparison to traditional methods, including greater threshing capacity, efficiency, and minimal grain breakage, as well as low cost of threshing (Goel et al., 2009;Kumar et al., 2002).The agricultural market in India is dotted with various kinds of threshers including those that are manually driven (Goel et al., 2009), as well as models that are powered by electric motors or diesel engines (Kumar et al., 2002).

Cleaning/Winnowing
Following threshing, the grains are cleaned to separate whole grains from the broken ones, as well as other external impurities such as dust, stones, sand, chaff, and other contaminants, making them fit for consumption and increasing their market competitiveness (Kumar & Kalita, 2017;Manandhar et al., 2018).Without proper cleaning, grains become vulnerable to pest attacks and fungal growth during storage, have an undesirable flavor and color, and can even harm processing facilities.(Kumar and Kalita (2017).However, due to poor handling and inefficient machinery, significant grain losses occur at this stage.According to Sarkar et al. (2013), grain losses during winnowing can amount to as much as 4% of total production due to spillage.
Winnowing, the most common method of cleaning threshed grains, is still practiced in India, normally using bamboo or woven basket winnowers, both of which are efficient but slow, laborious, and timeconsuming (;Sharma & Kalita, 2019).Bora () and Singh and Gite (2007) reported on the use of India-based hand-driven mechanical winnower, which in addition to lowering work drudgery, has a three-fold cleaning capability over the traditional methods, and produces 90% pure grain.Simple and eco-friendly technologies of these types could be a suitable alternative for large-scale winnowing, hence worthy to be scaled up and popularized among farmers.These kinds of simple and eco-friendly technologies could offer a viable alternative for winnowing on a large scale (Sharma & Kalita, 2019) thus deserving to be scaled up and promoted among farmers.

Drying
Following harvest, crops undergo a crucial drying process to reduce grain moisture content, preserve quality, minimize losses during storage, and lower transportation costs (Ali et al., 2015;Kumar & Kalita, 2017;Sahu et al., 2015).Insufficient drying might lead to microbial contamination and huge grain losses at later stages of the grain supply chain, such as storage and milling (Kumar & Kalita, 2017).Solarization or sun-drying, is the most common and cost-effective method for drying harvested grain crops in India (Mobolade et al., 2019).It involves exposing grains to the open sun to kill insects and remove excess moisture before they are stored (Ali et al., 2015;Dhande et al., 2020;Mobolade et al., 2019;Sahu et al., 2015).
However, this technique is not immune to unanticipated rains and external impurities such as dust, stones, hay, etc., as well as attacks by rodents, birds, and other harmful pests, as the grains are generally left to dry on an open area (Ali et al., 2015;Dhande et al., 2020).According to Kumar and Kalita (2017), unexpected rainfalls or unfavorable weather conditions such as cloudy and humid weather may impede adequate drying of grains, resulting in considerable losses due to fungal development as the grain will be stored at high moisture levels.Similarly, Ali et al. (2015) claimed that adverse weather conditions could occur during the drying process, resulting in grain quality degradation.Furthermore, this method is also subject to substantial handling losses, higher labor and space requirements, and takes a relatively long time for the grains to dry (anywhere between 5 and 45 days, based on the crop) (Ali et al., 2015).According to a study in Karnataka, India, traditional drying methods resulted in wheat and rice grain losses of 0.66 kg/q and 0.80 kg/q, respectively (Basavaraja et al., 2007).
Mechanical dyers, which are commercially available in the Indian agricultural market, offer an alternative to traditional drying processes (Ali et al., 2015).In comparison to sun drying, these grain dryers offer many advantages, including improved temperature and moisture content management, the ability to dry grains during the daytime as well as at night, less manpower requirement, reduced handling losses, and space efficiency (Ali et al., 2015;Kumar & Kalita, 2017).However, the widespread adoption of these mechanical dryers is constrained by a variety of barriers including their exorbitant initial cost, inadequate awareness among farmers about their availability, and an insufficient incentive system to adopt improved technologies, primarily due to the lack of remunerative prices for high quality-products (Ali et al., 2015;Kumar & Kalita, 2017).Ali et al. (2015) maintained that grain losses could be reduced by 6% by utilizing these mechanical dryers in conjunction with scientific storage practices, saving over Rs 13 500 million annually.However, Udomkun et al. (2020) observed that the majority of improved drying systems are powered by fossil fuels and electricity, leading to the increased emission of greenhouse gases and operational costs.Mahapatra and Imre (1990) pointed out that the use of fossil fuels to dry crops is environmentally harmful due to the production of pollutants such as Sulphur (S) and Nitrogen Oxide (NO), emphasizing the need to replace fossil fuels with clean energy sources (renewable energy resources).
Solar dryers are one of the few commercially available clean-energy-based drying technologies in India (Udomkun et al., 2020).However, only a few varieties are employed on a significant scale or are commercially available, aside from demonstration programs (Udomkun et al., 2020).Solar dryers have a number of cost advantages over traditional mechanical dryers, including reduced cost of fossil fuel and combustion machinery, in addition to being eco-friendly (Udomkun et al., 2020).Solar dryers, according to Mahapatra and Imre (1990), provide a variety of advantages over traditional sun-drying processes, including providing a substantial reduction in grain losses, as well as enhanced quality of the final output, shortening the drying time, reducing the harvesting time in general, allowing the land to be readied for the next cropping season, providing farmers with more options to earn money by producing high-quality products, etc.Therefore, making them more accessible and affordable would be very beneficial to lowincome farmers.

Storage
Storage is an essential stage in the grain supply chain in India, but it is also the stage with the highest grain losses (NAAS, 2019;Sahu et al., 2015).As grains are typically cultivated on a seasonal basis, grain storage is essential to ensure the sustenance and availability of seeds for the coming growing season (Kumar & Kalita, 2017).According to various studies, up to 70% of India's food grains are stored using traditional structures and practices such as Gourds, Kanaja, Wooden boxes/ Sanduka, Hagevu, Kothi, Earthen ports, Gunny bags, etc (Kumar & Kalita, 2017;Mann et al., 2016).
Traditional storage facilities are made from a range of locally sourced materials (mud, bamboo, bricks, reeds, wheat straw, paddy straw, calabashes, wood, cow dung, etc.,) and have various designs and applications depending on the agroclimatic conditions (Karthikeyan et al., 2009;Mann et al., 2016;Naveena et al., 2017).Moreover, Mann et al. (2016) maintained that these traditional storage facilities have been developed by farmers in various parts of India using their traditional wisdom and values.However, these structures are not completely immune to insect and pest infestation, making them vulnerable to substantial grain losses (Kumar & Kalita, 2017).Moreover, the majority of them have a relatively limited storage capacity (Kumar & Kalita, 2017;Mobolade et al., 2019).In an assessment of traditional storage practices in Tamil Nadu, India, Karthikeyan et al. (2009) mentioned that insect damage in stored grains and pulses could range from 10% to 40%.Comparing grains stored in hermetic bags with grains in traditional bags, Somavat et al. (2017) found that grains in hermetic bags suffered reduced insect damage from 0% to 0.33%.
Several improved alternatives to traditional storage methods, such as hermetic bags, metal or plastic drums, pusa bins, concrete/cement silos, metal silos, and so on, are also available at the farm level (Yadav, 2019).Moreover, the Food Corporation of India (FCI), Central Warehousing Corporation (CWC), and State Warehousing Corporations (SWC) own and operate warehouses that house bulk storage of grains and other agricultural commodities (Yadav, 2019).Considering the extent of grain losses associated with traditional grain storage structures and practices, these structures will be discussed in greater depth in the subsequent section.

Transportation
Transportation is a crucial part of the grain supply chain since it allows grains to move across various phases of the value chain, such as from the farm to storage sites, from storage sites to processing units, from processing units to market areas, etc (Kumar & Kalita, 2017).Traditionally, Indian smallholder farmers transport their grains from the field to their households by carrying them on their heads, backs, or shoulders, or by using bicycles or cattle-drawn carts, and sometimes by renting small motor vehicles, trucks, or tractors, especially for long hauls, such as from farm to market (Kumar & Kalita, 2017;Manandhar et al., 2018).However, if the grains are not adequately protected, there is a risk of grain spillage and damage during transit, as well as being contaminated with undesirable substances (Manandhar et al., 2018).Moreover, the widespread use of substandard jute bags during transport, coupled with poor road conditions, can lead to a loss of grains due to spillage and contamination from a variety of impurities (Kumar & Kalita, 2017).Kumar and Kalita (2017) observed that even the vehicles utilized in developing nations are not completely adequate for transporting grains.A study in Karnataka, India, reported wheat and rice grain losses of 0.51 kg/q and 0.50 kg/q, respectively, due to inefficient transportation, notably during the packing and offloading of grains (Basavaraja et al., 2007).
Among the traditional methods highlighted above, bicycle transport and cattle-drawn cart transport provide the cleanest form of transportation.However, a few clean technology tweaks are required to increase their capacity and efficiency.Kumar et al. (2019) presented a method for converting a regular bicycle into a solar-powered electric bicycle that the task in the least amount of time while reducing pollution.By securing significant investments through a public-private partnership, the government might help expand the reach of this and similar initiatives, allowing millions of farmers to transport their grains more effectively and sustainably.On a bigger scale, the government should encourage the increased use of fuel-efficient vehicles with a low carbon footprint, such as those powered by electricity, clean gases, lesser carbon fuels, etc.Furthermore, the government should make the necessary investments in rural transportation infrastructure and services, not only to cut transportation costs but also to alleviate poverty and enhance living and economic standards in rural areas.

Milling/Processing
In India, grains are dehulled and processed for food in a variety of ways depending on the nature of the grain, particular needs, and local customs (Kumar & Kalita, 2017).This process can be done by smashing grains repeatedly or by employing mechanical milling machines (Kumar & Kalita, 2017).Some of the commonly used traditional tools, and techniques in India, especially in rural areas, include; wooden mortar with a pestle, grinding stones, hand-controlled traditional milling machines created from locally available materials such as soil and straw, leg pounding, etc (Mishra et al., 2014).
While these traditional methods and tools are easier to use and more environmentally friendly compared to mechanical milling machines, they have a number of downsides, including being too slow and providing low output, being prone to grain losses, and being less viable when yield volumes are large (Mishra et al., 2014;Singha, 2013).In addition, Mishra et al. ( 2014) discovered that handcontrolled traditional milling machines consume a lot of time and require routine maintenance.According to Kumar and Kalita (2017), excessive grain breakage, leakages, and contamination with unwanted substances are among the primary causes of grain losses in traditional milling methods.In spite of their limitations, traditional milling methods, like hand-driven machines, are more environmentally friendly than mechanical milling machines that are powered mostly by fossil fuels or electricity.Their speed and capacity can be considerably improved with a few minor tweaks, such as combining two sources of working power (i.e., solar power and human power), allowing farmers to mill their grains more efficiently and sustainably.Figure 5 provides a brief summary of the most common traditional methods and practices used in India's grain supply chain.

Traditional grain storage structures and practices in India
The following section takes an in-depth look at some of India's most common traditional grain storage structures and techniques.Source (Kiruba et al., 2006;Mann et al., 2016;Mobolade et al., 2019;Shaila & Begum, 2021).
These are some of the most common traditional grain storage structures and methods that have been used by Indian farmers for decades, especially in rural areas (Kiruba et al., 2006;Mann et al., 2016).In the view of various authors (Kiruba et al., 2006;Mobolade et al., 2019), these structures and methods have lasted for decades and are still in use today because they have been developed by farmers in various parts of the country using their traditional wisdom, values, and readily available resources, along with scientific thinking.
Traditional grain storage structures are created from locally available organic materials, making them eco-friendly, affordable, easy to use, and readily available to farmers with limited resources (Karthikeyan et al., 2009;Manandhar et al., 2018;Nagpal & Kumar, 2012;Naveena et al., 2017;Sundaramari et al., 2011).Hence, the documentation and preservation of these structures and practices are vital for the sustainability of agriculture in developing countries.
However, traditional grain storage structures are prone to significant food losses due to their inability to provide total protection against moisture, rodents, mold growth, and other hazardous insects and microorganisms.In spite of this, the vast majority of these structures have relatively small storage capacity when compared to the total grain produced (Manandhar et al., 2018;Nagpal & Kumar, 2012;Naveena et al., 2017).As a result, India loses a tremendous amount of food grains during storage each year, putting food security and the sustainability of agriculture at risk.In light of this, it is essential to improve the storage capacity and efficiency of these structures through the application of modern materials and scientific knowledge.

Conclusion
The findings of this study indicate that traditional grain storage structures and practices contribute significantly to the sustainability of Indian agriculture.They are relatively inexpensive and easy to use, hence easily accessible even for farmers with limited resources.They are also made using traditional skills and knowledge that may be preserved by passing them down through generations, making them more sustainable and timeless.Moreover, they are created using locally available natural materials, making them safer for the environment and farmers.
However, the vast majority of traditional grain storage structures are vulnerable to significant grain losses because they are unable to provide complete protection against moisture, insects, rodents, fungus, and other harmful microorganisms.Moreover, most of them have a relatively small storage capacity compared to the total amount of grain produced.It is possible, however, to improve the storage capacity and efficiency of these structures by modifying them slightly using low-cost technology, modern inputs, and scientific knowledge.
To improve the storage efficiency of these structures, it is imperative to make them fully hermetic, to ensure better control of moisture absorption and reduce chances of pest infestations.Additionally, the majority of these structures need to be increased in size, so they can hold more grains.As almost 70% of grains produced in India are stored in traditional structures, upgrading these structures can help improve food security and farmers' livelihoods.Moreover, it can also help the country contribute to its sustainable development goal (SDG) target 12.3, which aims to reduce per capita food waste by half, at the retail and consumer levels by 2030, and minimize food losses across production and supply chains, including postharvest losses.

Limitations and further research
The major limitation of this study was the insufficient information on traditional storage methods, as demonstrated by the identification of only 43 articles within a 32-year timeframe .Furthermore, the study focused primarily on traditional grain storage methods; however, postharvest storage losses also impact other food crops in India.Future research should therefore extend the implications of this study to traditional storage methods for crops other than grains.On the other hand, our study could have missed important information about traditional storage methods by excluding papers published before 1990 and written in languages other than English.Due to the fact that these traditional knowledge systems have been in use since ancient times and are primarily passed down through generations in native languages, it would be beneficial for future research to include the studies that were published before 1990 and published in languages other than English, including native Indian languages.Furthermore, future research can further explore the following important research questions: (i) What are the farmer's perceptions about traditional storage mechanisms?(ii) What policy measures can be taken to preserve and improve these traditional grain storage structures and practices?(iii) What technological adjustments are necessary to minimize the limitations of these traditional storage mechanisms?(iv) In what ways can farmers minimize the losses associated with traditional storage practices?Moreover, future studies can assess the environmental impact of traditional storage methods and explore ways to make them more ecologically friendly.

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cylindrical grain-storing container made of bamboo and comes in a variety of heights.They are coated with a mud and cow dung mixture to avoid spills and misappropriation of grains.These kinds of structures are typically used in paddygrowing regions of the transition and hilly areas.

Figure 1 .
Figure 1.The flowchart of the literature selection process.

Figure 3 .
Figure 3.The area in India where the study was conducted.

Figure 2 .
Figure 2. Year of publication of included studies.

Figure 4 .
Figure 4.The type of grain crop studied.

Figure 5 .
Figure 5.An overview of India's grain supply chain's most common traditional methods and practices.Source: created by the authors based on the comprehensive review of the literature.

Table 1 . A summary of traditional grain storage methods used in India, especially in rural areas Traditional grain storage structures and methods Description Where it is common in India Advantages Disadvantages Possible improvements Citation(s)
Storage with ashes ad table saltIndian farmers commonly treat food grains during storage with ashes produced from various sources, such as wood, cow dung, etc., in order to keep fungus and other hazardous insects at bay.Some farmers also treat food grains with regular table salts before storing them in various locally made facilities such as jute bags, earthen pots, etc.