Abstract
Potato is known as a semi-perishable commodity and storage of both seed and ware potatoes which is problematic for most producers and consumers. The losses could be occurred during harvesting, sorting, cleaning, handling and packing, transportation, storage, distribution or marketing and processing. In Ethiopia most of the potato produced is mainly consumed as boiled, salad and stew preparations. Use of alternative recipes like french fries, crisps, flakes, flours, starches, pre-peeled potatoes and various snack food items has not developed well. Thus, the study was conducted to evaluate improved seed and ware potato storage, local farmers’ practices such as; storing under bed, storing in pit and extended harvesting for resource poor potato growers in central highlands of Ethiopia. The experimental design was complete randomized design (CRD) with three replications using two improved potato varieties. Improved ware potato storage diffused light store (DLS) were demonstrate to farmers through farmers field school (FFS) and farmers research group (FRG) participatory research approaches. FFS and FRG were organized from four districts and regular assessments were done for 105 days of storage period. From this study non-significant storage losses were observed. However, for the qualitative data, there were significant difference between the improved and the farmer’s/local storage practices in terms of taste, color change, sprouting and pest infestation.
The result revealed that storing potato on the ground under beds exposes the tubers for rapid sprouting, color and taste changes within few days. Especially in Haramaya district the tubers stored in the ground pits, according to the farmers practice, have rotten and excessively sprouted almost totally unlike the ones put in improved structures. On the other hand, extended harvesting has exposed the tubers for pest infestation. Even though, it is possible to use potato for ware through extended harvesting for some months, the losses due to pest infestation was extremely high. Thus, extended harvesting and other farmers’ practices are not effective for handling ware potato for long-term storage. It seems that the introduced improved seed and ware potato storage were the only effective option for potato grower farmers in central highlands where the temperature and relative humidity are suitable using locally constructed storage structure. Therefore, it was with great enthusiasm that the participated farmers highly interested with this improved practice and accepted to use the improved seed and ware potato storage structures for prolonged time and exploits the potential of this crop for food and nutrition security.
Keywords: Postharvest; Farmers field school; Farmer research Group; Ware potato storage
Introduction
Potato (Solanum tuberosum L.) ranked as the third most important food crop following rice and wheat and is consumed by over a billion people throughout the world [1,2]. Potato serves as a food and income security source and provides important nutrients. Potato has a high content of carbohydrates, significant amounts of quality protein, and substantial amounts of vitamins, especially vitamin C [3]. Potato production is expanding strongly in many developing countries accounting for more than half of the global harvest [4]. In Ethiopia, root and tuber crops are the third largest national food commodity, after maize and wheat, in terms of production [5,6]. Potato promises higher calorie per unit area production potential than any grain and can be produced, stored, and consumed without major technological inputs. Recent trends indicate that potato production in densely populated developing nations is on the rise [7]. According to [1] half of the total production occurs in developing countries that makes potato the third most important food crop globally [8,9] suggested that the high yield potential of potato per hectare of arable land, good nutritive value, and cooking versatility have resulted in a threefold per capita potato consumption in the developing world, from 6 kg capita_1 year_1 in 1969 to 18 kg capita_1 year_1 in 2009. The crop’s short cropping cycle allows it to serve as a hunger-breaking crop, and makes it suitable for intercropping and double cropping, especially in cereal-based production systems in Africa and Asia [10,11].
However, production of potato tuber is constrained by pre-harvest factors and postharvest losses, which in turn limit the volumes of good quality, produce reaching consumers [12] reported that potato is a source of food and cash income, playing an important role in the rural livelihood system of the densely populated highlands of sub-Saharan Africa. Ethiopia is one of the major potato producing countries in Africa as 70% of its arable lands in the highlands are suitable for potato production [13]. Potato being cultivated for more than 150 years in Ethiopia, it grows dominantly in the Northern Central and Eastern highlands of the country [12] and the recent reports of [14] stated that its production area has reached about 0.3 million ha producing more than 3.66 million tons in both Meher and Belg seasons.
According to [15], in 2017, potato yielded up to 20 tons/ha worldwide on average, whereas maize, rice and wheat had an average yield of 5.7 tons/ha, 4.7 tons/ha and 3.5 tons/ha, respectively. Potato is one of the most productive food crops, producing more dry matter (food) per hectare than cereals or any other cultivated plant. As such, it can significantly contribute to food and nutrition security. A hectare of potatoes provides up to four times the calories of a grain crop and up to 85% of the plant is edible human food, compared to around 50% in cereals. Potato produces more food per liter of freshwater used through irrigation than cereals and thus is more sustainable to mitigate the effects of climate change. Over the past 20 years, potato production has significantly increased in developing countries in Asia, Africa and Latin America by 89, 14.5, and 4 million tons, respectively. In Africa, the potato production and harvested areas more than doubled over the last 20 years. Average potato consumption in East Africa has grown by approximately 300% over the past two decades, yet yields are low. The major bottlenecks to higher potato yield and reliable supplies in Africa are limited or no access of farmers to high quality seed tubers of improved varieties, poor crop husbandry practices (e.g. disease and soil fertility management), and poor post-harvest management [16]. A promising alternative to traditional clonal propagation of tetraploid potatoes is the production of hybrid true potato seeds: planting 10 hectares, for instance, takes just 200 grams of easily transported true seeds, compared with 25 tons of perishable seed-tubers. It was introduced in Africa at the end of the 17th century by Christian missionaries through the formation of small plantations. Soon after, potatoes quickly became part of the feeding habits of both rural and urban populations. As in Europe, potato production could contribute in the fight against food insecurity in the sub-Saharan African countries [17].
So far, different attempts have been made to come up with an appropriate agronomic and pre-harvest management to increase potato tuber productivity in Ethiopia [18-20]. The major constraint of potato production in Ethiopia includes poor quality seed, poor agronomic practices, poor pre and post-harvest handling, marketing and transportation systems. The percentage losses of potato due to post harvest handling are estimated to be 20-25% [21]. Potato production is seasonal, and it lack proper storage methods such as cold storage. In agriculture sector, a lot of emphasis has been put on research and development of agriculture production and fewer resources in post-harvest development. Potato is a bulky and fleshy crop with a short storage life therefore needs careful handling, packaging and storage. In Ethiopia, post-harvest losses of horticultural crops may be estimated for about 15 to 70% at various stages [18]. Potato is known as a semi-perishable commodity and storage of both seed and ware potatoes which is problematic for most farmers, as storage losses can reach 50% and sometimes higher [22]. Lack of proper storage systems are among the main factors contributing to the low yield of potato in the region, which is the case at the country level also [23]. Furthermore, market price of the product and marketing systems are also problematic [24]. According to [25] unavailability of proper potato seed storage forces the farmer to sell immediately during harvest with low price, whereas availability of proper storage facilities allow farmers to sell their potato tuber as a seed during planting or in the later season with higher price compared to the immediate sell.
Farmers stored potato either for seed or ware using various traditional storage mechanisms. These traditional storage facilities do not allow the growers and consumers to store potato not more than three and half months without deterioration [24]. However, farmer requires good storage either to use tubers of their own harvest as a seed source to postpone sales to get better market price and for household consumption in the later season. Hence, improving food security requires a comprehensive approach towards post-harvest managements using new strategies and/or technologies to ensure the higher value of post-harvest produces. Therefore, the major post-harvest losses of potato and its strategy to mitigate the problem were described.
Major potato post-harvest losses
In the absence of storage technologies for seed and ware potatoes, farmers keep potato harvest in the field for extended period in Ethiopia. This practice exposes the tubers for insect attack which reduces tuber yield and quality significantly. A study on extended harvesting period in Alemaya revealed that yield of marketable tubers was reduced by 60% when tubers were harvested at 210 days after planting as compared to a harvest at 120 days [26]. Similarly, [27] reported significant yield reductions (70-100%) when harvesting was delayed from about 125 days to 230 days after planting. Estimates of the production losses in developing countries are hard to judge; but some estimate the losses of potatoes, sweet potatoes, plantain, tomatoes, bananas and citrus to be very high. About 30-50% of the total produce (1.3 million tons) is lost after harvest. Globally, horticultural crops postharvest losses have been reported at 19% for the USA at an estimated annual loss of $18 billion [28]. Higher losses have been reported for African countries ranging between 15%-30% of the harvested product [29].
Post-harvest losses are mainly caused by different physical, environmental and biological factors which include mechanical injuries, extreme temperatures and pathogens [30]. According to [31], the causal factors enhance post-harvest losses through changes in the chemical composition and physical properties of the tuber in the process of respiration, loss of moisture from the tuber, sprouting, and spread of diseases. In the light of the little information generated on the major factors of post-harvest losses in Ethiopia, some of the principles in post-harvest management and the basic environmental and physiological causes of post-harvest loss are discussed as below.
Physical, biochemical and physiological losses
Physical losses include the various responses of tuber to excessive or insufficient heat, cold, or humidity. Proper storage is required to allow ventilation and heat exchange to maintain proper temperature level, to reduce the air and gas exchange (oxygen, carbon dioxide, and ethylene) and to minimize water loss. Losses caused by mechanical injury are usually overlooked. Physical injury is a loss by itself, and it can result in secondary physiological and pathological losses. Mechanical injury can occur at hilling, harvesting, and handling operations such as grading, transporting and marketing. Among tubers from the same cultivar, the degree of damage is influenced by the dry matter content and turgidity of the tubers [32]. High dry matter content causes higher braising. Good level of care is needed during harvesting and handling operations to minimize damage caused on tubers. The damaged tuber always has a shorter post-harvest life than the undamaged tubers [32].
Respiration
Potato tubers respires using sugars converted from starch. Therefore, respiration reduces the starch content of the tuber. During respiration, the tubers use oxygen from the air and produces water, and carbon dioxide and heat. The most important effect of tuber respiration is the production of heat and its subsequent effect on storage temperatures and the action required to control it [32]. If the respiratory heat is not removed, the temperature of the potatoes rises by 0.25 °C per 24 hours. The rate of respiration is dependent on the temperature and is minimum at about 5 °C. Tubers that are stored at relatively higher temperature lose their moisture after some time and become unfit for consumption or for prolonged storage as seed for the coming season planting. The problem was observed in seed potatoes stored in diffused light store (DLS) at Shashemene area. Fresh weight of tubers is considerably reduced in storage both due to respiration and water loss. It was observed that mean tuber weight loss as high as 23% was recorded when potatoes were stored in naturally ventilated storage for 120 days (Table 1). The tubers were dry due to excessive moisture loss and they were not suitable for planting after 6 months. This was due to relatively higher temperatures and dry air that enhances respiration and consequently desiccates the stored tuber.
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