Program 6

Improved Rustic Storage in South Asia
S.G. Ilangantileke¹, V.S. Khatana¹, J.P.Singh², and D. Kumar²

Materials and Methods
Results and Discussion
Conclusions

India ranks second only to China among the Asian countries in potato production. The country produced 20.3 million t of potatoes from 1.26 million ha area during 1994-95. If the trend of the 1990s continues, total production could reach 28 million t by the year 2000. Thus the country should be ready to handle an additional 8 million t of potatoes within 5 yr. This may be a difficult task, particularly when postharvest facilities to handle existing potato production are limited.

Potato production is mainly concentrated in the northern plains comprising the states of Uttar Pradesh, Bihar, and West Bengal. About 81% of the total potatoes produced in the country are harvested from January to April and are available for market, but only 28% of those potatoes are demanded as ware potatoes during the period. This creates a surplus of 53% of ware potatoes, which have to be used or stored over the next 6 months from May to November. In addition, about 10% of the total potato produce harvested in the same season needs to be stored as seed to be used for the next production year.

A major portion of the harvested potatoes are stored in cold stores for long-term storage. Potato prices are lowest at the peak harvest season, generally from early February to early March when the major crop of potatoes is harvested in Uttar Pradesh. The usual trend in price variation results in about a 50% increase in prices within 2-3 mo of the peak harvesting period.

The available cold-storage capacity in many of the potato-producing states in India falls short due to the high demand experienced during the harvest. The installed capacity of cold stores is 8.7 t. Estimates indicate that 92.5% of total cold-store space is used to store potatoes.

Assuming that the entire existing installed cold-storage capacity for potato operated at full efficiency, only 40% of the potatoes produced in the country could be cold-stored. Because of the shortfall of cold-storage capacity and low prices experienced at harvest, about 4 million t of harvested potatoes are still traditionally stored, since this is the only choice left with farmers.

Traditional storage practices vary by districts within a state. The end use of the harvested potato governs the storage practice. It could vary from domestic storage in households, mainly for family consumption, to commercial storage in traditional structures, heaps or clumps under trees in orchards, and underground pit-storage structures found in the state of Madhya Pradesh. The main force behind pit storage, where potatoes are kept for over 2 mo under ambient conditions, is the demand for potatoes for processing. In humid West Bengal, potatoes are stored in ordinary rooms, generally on raised bamboo platforms. Storage in Uttar Pradesh begins in late winter and the temperature increases rapidly from late February onward. The increasing temperatures result in heavy storage losses. Considering FAO estimates of 17% postharvest potato losses in India, then the monetary losses for a season could be approximately US$55 million. Farmers who are unable to avail themselves of cold-storage space will benefit from improved traditional storage methods that decrease losses and increase their income.

Earlier studies indicated that rustic stores with evaporative cooling to lower temperatures and increase humidity provide a better storage atmosphere than the traditional storage systems. But research is limited and the effectiveness of the storage system on-farm has not been studied. We therefore undertook rustic-storage trials in Uttar Pradesh to test such storage systems in farmers’ fields for ware potato storage. We also conducted storage surveys to determine the status of traditional and cold stores in potato-growing districts.

Materials and Methods

Over the past three years, CIP constructed and evaluated evaporative cooled rustic stores (EVS) in farmers’ fields. The storage experiments were done in collaboration with the Indian Council for Agricultural Research (ICAR) in the Central Potato Research Institute (CPRI).

The actual experimentation was done in collaboration with scientists from the Central Potato Research Station (CPRS), in Meerut District, and in farmers’ fields in Meerut, Muzaffarnagar, and Farrukhabad districts of Uttar Pradesh. Storage surveys were conducted in collaboration with scientists from the CPRI. Eighteen improved EVS were constructed in different farmers’ fields using locally available material such as brick, mud, wood, and thatched roofs (Figure 1). Cement and bricks were used to build the evaporative chamber at the bottom of each store. Cement troughs were constructed with an arrangement of brick channels, to increase the movement of air under the store. Sand used as the evaporating surface was placed in the troughs to a depth of 6 cm between the brick channels and was kept wet during potato storage. The water level was kept at about 0.5 cm above the sand to ensure adequate moisture for evaporation.

A locally constructed wind turbine was fitted to the roof of each store. The suction of the turbine was set to minimize desiccation of the stored potatoes. Westerly winds prevailed during most of the storage season, so the stores were constructed facing the north-south direction. The easterly lip of the water trough was higher than the westerly lip to restrict the hot, dry air moving through the trough to the outside. This enabled a longer residence time for the hot, dry air inside the water trough, thus providing better evaporation.

The potatoes were stored on bamboo mats placed on the brick channels inside the store. Walls were plastered with about 3 cm of mud and straw mixture to give better insulation. Holes (2 cm diam) were made on the side walls of the eastern and western side of each store at a height of 1.5 m to measure temperature inside the store using a long-stemmed thermometer. The holes were sealed with mud between temperature readings.

Initial temperature and relative humidity (RH) data were collected at the time of filling stores and regularly thereafter. At the CPRS store, dial thermometers were permanently installed with the probes in direct contact with the stored potatoes to give temperature of potatoes during storage. A Stevenson’s screen was fixed for ambient temperature and RH measurements. Continuous monitoring of store temperature and RH at the CPRS store was done using a continuous-recording Thermohydrograph installed at a height of 1.6 m. Observations on potato quality were taken at 2-wk intervals by opening the stores early in the morning when the difference between the inside and outside temperature was a minimum. Similar observations were made in farmers’ fields during regular visits to monitor the progress of the experiment.

Potatoes for storage were sorted and weighed; damaged tubers were discarded. Stores were filled in March. The varieties stored were Kufri Bahar, Kufri Badshah, Kufri Chandramukhi, JI-5857, and TPS families. Potatoes were piled to a maximum height of 1.5 m. The effective storage capacity of the stores was 10 t, although in some instances the capacities were increased at farmers’ requests and at their cost. The quantity stored ranged from 2.5 t to as much as 14.6 t. After the stores were loaded, their doors were sealed with mud to give better insulation. Moisture or weight loss of potato in the improved rustic stores as well as in the heap/ordinary room was evaluated by placing 5-9 10-kg bags of potatoes in different places (bottom, middle, and above the stored potatoes).

Potatoes were stored under these conditions until farmers decided to sell, based on the prevailing market price. Observations taken on the day of selling the stored potatoes were (1) number of sprouted tubers, (2) number and weight of rotted tubers, and (3) the final weight of good tubers. The prevailing price of potato in markets in close proximity to the stores under study was noted at the time of both storage and sale.

Results and Discussion

Cooling efficiency
Daily and weekly temperature data taken from the beginning of storage in March to 1 June (the time of selling) indicated that there was a uniform reduction in temperatures between ambient and the inside of the store. The morning (0800 h) ambient temperatures were not significantly different from the temperature inside the store (Figure 2). The outside temperatures in the morning began to rise significantly from March to the end of May. The difference between the temperature from 0800 h to 1400 h averaged around 16^oC.

Temperatures increased from about 35^oC in March to more than 40^oC at the end of May for readings taken at 1400 h; inside the EVS the temperature recorded at 1400 h was 12-19^oC lower than the ambient. The turbine influenced uniform upward movement of evaporating moist, cool air through the potato pile and reduced fluctuations in temperature inside the store. The temperatures inside the store observed at 0800 h and 1400 h were not significantly different. Therefore, early morning hours are the best times to inspect the stores.

The airflow provided by the turbine reduced the desiccation of potatoes in storage, and maintained a uniform temperature inside the store depending on outside temperature and humidity.

Reduction in losses
In 1995, average total losses were 11.3% in Muzaffarnagar and Meerut, and 20.4% in Farrukhabad. The losses were substantially less (10%) at the research station, which may be because of better maintenance and management of the store at the research farm. The minimum losses of 3.5% were observed at a farm in Bopada village in Muzaffarnagar. This farmer was very progressive and worked on the construction of the EVS, and took a keen interest in monitoring temperature and water levels in the trough.

During 1996, farmers of Farrukhabad suffered losses of 2.8-10.4%, over a storage period of 24-61 d. The losses in potatoes stored for 61 d in the ordinary room were 13.9% compared with 10.4% in EVS during the same period (Figure 3). The reason for short-duration storage in some stores was the sale of potatoes by farmers when the prices were comparatively higher than at harvest.

In 1996, losses of the EVS in Meerut varied from 6% to 11% over a storage period of 43-53 d. The farmers who stored in March, when temperatures were still low, had only 8% losses in an 85-d storage period. Rotted tubers varied from 0.7% to 3% and sprouted tubers varied from 5.5% to 98.7%. Maximum sprouting was noticed in the case of the farmer who stored the longest (85 d).

Farmers in the study area without storage facilities heaped their produce. The losses in heaps were 4.3% and 7.5% in storage periods of 33 and 35 d, respectively. The 7.5% losses in heaps during 35 d was higher than a 6.9% loss in EVS during 47-d storage. Farmers who stored their potatoes in heaps were paid lower prices because of the low quality.

There was a significant reduction in temperature and increase in humidity inside the EVS during the hot, arid months from April to June, thus maintaining a higher quality of stored potatoes. Weight losses in potato were influenced by variety, preharvest and postharvest management practices, store construction, and store management.

This study was the first major attempt to take the technology of rustic storage to farmers’ fields. The results indicate that potatoes stored in EVS had lower weight loss and higher quality at sale time. An added advantage is that the EVS provided a convenient means of keeping potatoes in bad weather, whereas those stored in heaps were exposed to rain and desiccation.

Losses in the Farrukhabad stores were higher than those in Meerut and Muzaffarnagar. There was no climatic difference in these districts and the losses may be attributed mainly to leakages and poor management of water in the troughs. Although stores were located in close proximity to tube wells, the nonavailability of an assured source of power and the lethargy of farmers to keep the sand surface moist resulted in lower cooling efficiencies.

Lower losses in 1996 at all sites compared with 1995 strengthens the line of thinking that store management plays a key role in potato storage. Farmers were more knowledgeable about potato storage during the second year of the trial and thus reduced their storage losses.

Profitability
Profitability of an improved technology is the main factor that influences adoption. The EVS technology was more profitable than the farmers’ practice of storing potatoes in houses and in heaps. In Farrukhabad, the price of potato was Rs 2.1/kg ($0.06/kg) when stores were filled. It had increased to approximately Rs 3.75/kg ($0.11/kg) after a period of 24-61d. The gross return was 11% higher per kg of potato stored in EVS than in ordinary rooms and in heaps.

In Meerut, overall weight loss in potatoes stored in EVS varied from 6% to 11% over a storage period of 43-85 d. The gross returns in heaps ranged from Rs 189/t ($5.30/t) to Rs 494/t ($14/t) compared with Rs 269/t ($7.62/t) to Rs 1,030/t ($29/t) for potatoes in the EVS. The highest gross return was earned by a farmer who stored for the longest period (85 d) in the EVS, because he received the highest sale price in June. But when net profits are considered, heaping of potatoes is more profitable because of the high cost of constructing EVS. Storage in heaps, however, has a risk of high rottage due to rain. Neither can potatoes be stored as long in heaps as in EVS.

More than 20% of the potatoes grown in the Uttar Pradesh plains are used for seed and stored in cold stores after harvest. Uttar Pradesh is traditionally a seed supplier to the rest of the potato-growing areas and therefore depends heavily on cold stores. This has resulted in a concentration of cold stores in Uttar Pradesh. Any new technology must have significant advantages over cold stores, traditional heaps, and other structures. The cost of EVS is still higher than that of the heaps or other structures, and not significantly lower than the cost of cold storage per kg of potato.

The EVS has a definite advantage for farmers wanting to dispose of their potatoes in the early months of storage, for those who do not want to be at the mercy of cold-store owners, and for those unable to avail themselves of cold-store space at harvest. If the storage cost of the EVS could be significantly reduced to below the cost of cold storage, then EVS could be justified for short-term storage. If not, Uttar Pradesh farmers will continue to use cold stores, which guarantee better produce quality even though their availability fluctuates. Table 1 compares costs and returns for the EVS, heaps, and pits with the cost of cold storage.

Adoption domains
The cooling efficiency of the EVS during the hot, arid months from April to June gave a higher-quality potato to the market. But farmers have yet to understand the need for overall management of both produce and stores during the storage period, if the technology is to be successful.

The Uttar Pradesh plains are semiarid. Temperature rises to about 44 °C in summer and drops to about 3-4 °C during winter. The states of Madhya Pradesh and Gujarat have temperatures similar to Uttar Pradesh, but the humidity is even lower. The scope for EVS adoption is higher in these three states than in all the other potato-growing areas in India. Increasing interest and demand for processed potato, mainly for chips, is creating a significantly increased demand for indigenously stored potatoes. Large processing companies pay premium prices for good-quality potatoes that have not been in cold storage in Madhya Pradesh. These potatoes have lower sugar contents and optimum processing quality.

In Madhya Pradesh, Gujarat, and Karnataka, cold-store space falls much short of the optimum level of 55% of the total produce (Table 2). Cold-store charges in these states are much higher than in Uttar Pradesh. Farmers in these states may find the EVS technology quite profitable for ware and for processing. These states cater to the needs of potato processors by storing potatoes in indigenous structures, built with high investments. The investment in EVS is significantly lower than the investment in traditional stores, which do not have the cooling and lower weight loss advantage of the EVS.

Conclusions

Rapidly increasing potato production in India is placing a strong demand on the currently available, limited postharvest facilities, especially those to store ware potatoes. By the year 2000, the country needs to be ready to handle an additional 8 million t of potatoes, although cold-store space is limited.

Store losses in the different districts varied from 4% to 11%. Loss depended mainly on the initial condition of potatoes going into storage and the duration of storage. Other factors such as store management and water control in the EVS troughs also contributed to losses. Losses in heaps were lower than expected, but still higher than losses in EVS for a similar duration.

Profits (based on prevailing prices) of farmers were significantly higher for those who stored their produce efficiently for 2 mo or more.

Postharvest management of potatoes before storage and the management of stores after filling affect EVS efficiency. Proper management of the total storage system provides a better quality of stored produce.

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1 CIP, South and West Asia Regional Office, New Delhi, India.
2 Central Potato Research Station, Modipuram, India.