Turmeric (Curcuma longa L.) is one of the spices produced in Ethiopia entirely by smallholder subsistence farmers in southwestern part of the country. It composed of a significant proportion of smallholders’ income and offered a good opportunity for diversification of the existing Arabica coffee-based cropping system of Southwestern Ethiopia. This region has very suitable agro  ecology   for   turmeric   production.   Its commercial cultivation in Ethiopia is picking up and is likely to become a cash crop with good economic return especially for resource poor farmers. It has also been commercialized in large private farm and huge investment projects at national level, which indicated the bright future of the crop in Ethiopia (Derese, 2009; Masresha, 2010).

Turmeric is a well-known component in many Ethiopian dishes (local stew, "wot") (Girma et al., 2008; Edossa, 1998). It has a characteristic flavor and yellow in color and also used in cosmetics (facial preparation and creams) and ayurvedic drug preparations, antiseptic and also anti-inflammatory (Habetewold et al., 2018; Purseglove et al., 1981). In addition to richness of rhizomes in curcuminoids pigments (6%) and essential oils (5%), it also contained 69.43% carbohydrate, 6.30% protein, 3.50% mineral and other important nutrients on dry weight basis (Olojede et al., 2005). It is also used as coloring power in different foods and beverages preparations; color extracts from turmeric are employed in textile industries, soap and cosmetic factories as well as in pharmaceutical preparations (Girma et al., 2008; Purseglove et al., 1981).

Turmeric is one of the exported spices from Ethiopia; Southwest Ethiopia produce turmeric as a cash crop and many livelihoods are dependent on it. India is the world biggest exporter and producers of turmeric, whereas, Ethiopia is the exporter and producer of turmeric in Africa. Tepi National Spices Research Center (TNSRC) commenced several research experiments and developments since the introduction of the crop to Ethiopia in 1970s with the objective of identifying best turmeric production and processing technologies and practices that could be served as the best alternative crop for export diversification and alleviation of poverty in Ethiopia (Olojede et al., 2005). In Ethiopia, turmeric is mainly produced in southwestern part of the country (Sheka, Benchmaji and Keffa zones). However, recently major ginger producing areas including Wolayta zone shifts the land to turmeric production because of devastation of ginger by bacterial wilt and good demand for turmeric (Habetewold et al., 2018).

Turmeric is a tropical plant and thrives well from sea level to 1500 m above sea level, at a temperature range of 20 to 35°C with an annual rainfall of 1500 mm or more. Though it can be grown on different types of soils, it thrives best in well-drained sandy or clay loam soils with a pH range of 4.5 to 7.5 with good organic matter status (Jayashree et al., 2015).

In 1972, two turmeric accessions were introduced from abroad for adaptability study at Jimma, Metu, Bebeka, Tepi, Wenago, Awasa, Mugi and Bako (Edossa, 1998). In the next research activities, eight accessions were included in the evaluation process and two improved varieties namely Ind.48/72 (Dame) and Bonga.51/71 (Tepi-1) were released in Ethiopia. The released varieties showed high yield (250-300 quintal fresh yield per ha) and qualities standards such as oleoresin and essential oil contents were in the range of the international standard. List of accessions evaluated in the national variety trial is shown in Table 1. Maintenance of these materials continued as the germplasm will be useful for future research.

Land selection

Turmeric should not be cultivated on sloppy area as down moving water can erode and can deplete the soil around the plant and exposing seed or sprouted rhizome significantly reduce the growth, production and quality of turmeric. The land should be thoroughly ploughed three to four times before the rainy season.

Land preparation

Before planting the prepared seed rhizomes, the land should be free of any obstacle (roots, stones or gravels, etc.) that could hamper the free horizontal expansion of the rhizomes. The soil should be very fine and workable, free of marshy condition. Studies on identification of suitable land preparation methods indicated that raised bed preparation gave maximum fresh rhizome yield (33.55 t/ha) while the lowest fresh rhizome yield (20.97 t/ha) recorded from flat land (Girma et al., 2008) (Table 2).

Propagation technique

Commercially, turmeric is vegetatively propagated particularly with the divisions of its rhizomes. Three types of planting materials can be prepared from the  rhizomes. These are mother rhizome (arises from the original planting material), daughter rhizome (secondary rhizomes) and finger rhizome (split rhizomes). Seed rhizomes need preparation before planting; select healthy, reasonable size and weight and at least with one or two buds. Based on soil types and rainfall condition of the area, planting can be in furrow, on flat beds and on ridges (Girma et al., 2008; Purseglove et al., 1981).

Planting date

Turmeric is rhizomatous spice that requires high moisture particularly higher and longer rainfall distribution from time of planting to maturation. Therefore, determination of suitable planting time to get enough moisture is an important issue. Study on suitable planting time in Southwestern Ethiopia was conducted and mid of March to first week of April was recommended as the highest rhizome yield (18.48 t/ha) recorded in this period (Table 3). This recommendation can work for various agro ecologies with some modifications in specific areas.

Seed rhizome storage

Three to four-month time gap between harvesting and next planting of ginger can lead to significant loss of planting materials and this necessitated devising appropriate storage method(s) of seed rhizome turmeric. Ginger and turmeric have similar seed rhizome preparation and management technique as they have almost same morphology and similar storage practices can be applied. For ginger, the following experiences of storage of ginger were investigated:

(1) Under thatched roof shelter on the ground

(2) Under thatched roof shelter on one meter raised structure or bed

(3) In pits covered with thin grass mulch

(4) Buried in pits

(5) Under tree shade covered with mulch materials

According to the result obtained from this research, less percent of shriveled rhizomes and maximum fresh rhizome yield of 28.24 and 27.52 t/ha were obtained from seed rhizomes kept under tree shade covered with mulch materials and from seed rhizomes kept under thatched roof shelter on the ground (Hailemichael and Seyoum, 2016). The results disclosed that there are more safe options to keep seed rhizomes of turmeric and ginger which could be designed and constructed easily at farmers' level. The various options can be applied based on the environmental condition. 

Spacing or seed rate

An experiment with three different spaces between rows and four different spaces between plants was conducted at Tepi. Accordingly, spacing of 30 cm × 15 cm between rows and between plants that yield 30.59 t/ha (fresh) equivalent to 6.17 t/ha dry, has been recommended (Table 4).

Weed management

Turmeric and ginger are very sensitive to weed competition. The first two to three or four months of planting rhizomes are very critical to manage weed. If the field left un weeded in the mentioned periods, the weeds will be very competent and affect the full establishment of the turmeric plant. And, the reverse will be observed if timely and appropriate management practices are applied (Girma et al., 2008; Purseglove et al., 1981).

Since turmeric is slow germinating and growing crop, repeated hand weeding is required to save the crop from noxious robust growing tall weed species such as Gyzotia scabra, Bidens ploynchyma, Nicandra physaloides and Caylusia abyssinica. The result has confirmed that early hand weeding between 30 and 45 days was critical for vigorous growth of turmeric. The finding reported by Tadesse et al. (2015) has proved that mulching at planting was found to be good agronomic practice in suppressing weed growth and reducing the frequency of hand weeding in turmeric under Metu condition which can be applied to similar agro ecologies. Hence, based on the present finding, turmeric can be mulched at planting and supplemented by two hands weeding at 60 and 90 days or at 45 and 75 days after planting for high yield of turmeric. Deshmukh et al. (2018) also investigated and reported that in India integrated use of either Pendimethalin 1 kg/ha or by Metribuzin 0.7 kg/ha (0-5 DAP=days after planting) followed by straw mulch 10 t/ha (10 DAP) followed by one hand weeding (75 DAP) was proved very effective for weed control and for attaining the highest productivity and profitability in turmeric.

Intercropping

In photosynthesis performance, turmeric is between C4 and C3 plants and can perform in medium shade condition. It can be intercropped with crops like chilli, onion, French beans, eggplant and maize. Turmeric can also be grown as intercrop in coconut and areca nut plantations. As a whole, turmeric intercropping with coffee was found appreciable to stabilize yield advantages and gross economic returns, particularly at the early year of stand establishment (Table 5). Hence, the small holding farmers can more or less buffer against crop failure and low market price of one crop.

Harvesting

Because of less awareness on quality aspects or other agendas, Turmeric farmers in Ethiopia sometimes keep the rhizomes not harvested at end of season. And, this type of practice can have significant negative influence on the quality of turmeric. So, farmers need to be trained and start to follow the suitable harvesting stage for yield and quality. Maintain the rhizomes underground for more than one season, meaning facilitation, the loss of quality. This type of farmers’ practice is to maximize the rhizome yield, however, it has been reported (Purseglove et al., 1981; Girma et al., 2016) that the quality parameters of turmeric reduced and the produce is less competent in the local and foreign market. 

Two types of research activities; four different harvesting cycles (1, 2, 3 and 4 years cycles) and five months of harvesting stages (7, 8, 9, 10 and 11) after planting were conducted at different years (Edossa, 1998; Girma et al., 2016). Late harvesting years or months resulted in high rhizome yield (29.32 and 19.344 t/ha) from first year and fourth year cycles, respectively, increased fiber and reduced extraction qualities. The results were supportive to the report by Purseglove et al. (1981). Although leaving turmeric rhizomes in field for more seasons resulted in continuous physical rhizome yield increase, the extraction quality that has a negative correlation to duration of maintenance and the production costs should be investigated and this type of activity is not recommended. The quality of turmeric is influenced by harvesting stage and variety. Extraction yields such as oleoresin from turmeric are the critical quality factors considered for industrial utilization.

The highest essential oil yield in dry weight basis of the turmeric rhizomes was 5.14 and 5.13% when the variety Bonga. 51/71 (Tepi-1) was harvested 8 and 7 months after planting, respectively. On the other hand, maximum oleoresin content was obtained in Bonga.51/71 (Tepi-1) and Ind.48/71 (Dame) (11.45 and 11.21% respectively) while the lowest (10.55%) was obtained in Pack.6/82. Harvesting of 7 to 9 months after planting is suitable for these varieties in order to maintain their quality as the varieties will get more fibrous as maintained for more months in the field.

Harvesting takes place usually when the lower leaves of the plant dry and turn yellow and pseudo stems withers and start to lodge. After removing the upper leaves, the rhizomes will be removed from the soil by use of fork or another appropriate tool (Girma et al., 2008). The total production and productivity of turmeric is very low compared to its potential in Ethiopia. Its contribution to the spice export compared to its potential is yet unexploited due the weak link of production and marketing. Farmers used low yielding varieties and traditional harvesting and processing techniques (Derese, 2009). According to Addisu (2014), the national productivity of turmeric in Ethiopia was 2.4 t/ha, while it is 4.0 t/ha in India. Yield potential of turmeric in the research stations was reported as high as 6.2 t/ha dry rhizome which is within the acceptable range of world turmeric productivity (Girma et al., 2008).

Turmeric polishing

The dried rhizomes are polished (Figure 1) to remove the scales and root bits. This helps remove the corck layer of dried rhizomes and enhance the deep inherent yellow orange colour (Purseglove et al., 1981). In traditional method, the dried rhizomes are loaded in a bag and beaten on a hard surface. In the improved method hand operated barrel or polishing drum mounted on a central axis is used for polishing. The barrel or drum has an expanded metal mesh into which dried rhizomes are loaded and rotated. Polishing is carried out by  the  action of abrasion of the surface against the mesh and rubbing between the rhizomes (Girma et al., 2008). In Ethiopia, farmers grind uncooked turmeric rhizomes with mortal and pestle (“mukecha”). They mix the grinded turmeric juice with lemon juice and apply on the boiled rhizomes. The purpose of coating turmeric with such solution is to produce the yellow color of the turmeric and to protect the rhizome from weevil attack and increase storage time. This step of adding solutions on rhizomes is a value adding mechanism for farmers. This process is not currently practiced by farmers as traders have resisted buying such as coated turmeric rhizomes. The big traders are processing by themselves at their warehouses after they buy the dry rhizomes from farmers. This has its own implication for reduction of price (Derese, 2009). Results of comparison of the effect of different polishing or peeling practices and techniques exercised around Tepi areas were evaluated and presented in Table 6.

From the evaluation of various polishing or ‘peeling’ techniques, the best preferred yellow orange colour was obtained when the cured turmeric fingers were rotated in a polishing drum. Though very laborious, polishing or ‘peeling’ using mortar and pestle with the addition of citrus was found to yield products comparable with a rotating drum resulting deep-yellow coloured products, while other practices resulted in a bit inferior products (Fantahun and Teklu, 1995) (Table 6). Manual polishing drum could be adopted by farmers, may be through cooperatives. With  this,  farmers  can  benefit   from the turmeric product by producing standard quality turmeric (Habetewold et al., 2018). Currently, more turmeric processing factories are being established as the business confirmed promising. Partial view of postharvest process is as shown in Figure 1.

Quality

Quality of turmeric is influenced by a number of factors; type of cultivar planted, environment of production, field management, postharvest practice and processing (Purseglove et al., 1981; Girma et al., 2008). Quality parameters of turmeric can be physical (appearance, surface structure, content of extraneous matter, etc.) and extraction content of essential oil and oleoresin are important ones. So far, the varieties supplied to the production  system   in   Ethiopia   fulfil  the  major  quality parameters set by the market. Harvesting stage of Turmeric rhizomes significantly influenced more of the quality parameters. In general, the varieties Dame and Tepi-1 showed higher extraction quality performances when harvested from 7 to 8 months after planting (Purseglove et al., 1981; Girma et al., 2008, 2016) (Table 7). Whereas, harvesting 9 to 11 months after planting improves the physical quality parameters; dried rhizomes look slender, large size, from yellow to deep yellow orange colour, double use (whole-home use, extraction) (Girma et al., 2016).

Products and end use

The primary product of turmeric is the cured dried rhizome. This is valued principally for its yellow-orange coloring power in textile industry. Second to this, it contains an appreciated aroma and flavour that makes it considered as a spice. Turmeric is used directly as a spice or colouring agent in the ground form and also for the preparation of the solvent extracted oleoresin (Purseglove et al., 1981). Turmeric is an important spice in every Ethiopian kitchen and commonly used as an ingredient in the preparation of local sauces 'Wot'. It is the most favoured spice by house-wives. As a characteristic of more of the spices plants and products, it has significant use in medicinal value (Purseglove et al., 1981). There are reports indicating that 3962.03 t of turmeric was produced in Ethiopia in three years, while Monika and Addisu (2018) mentioned values of USD 1.26 million as well as export of 1233 MT rhizomes in different seasons.  

Ethiopia has wide agro ecology, and turmeric has wider adaptation from lowland to mid altitude areas. Currently, two improved varieties released with production packages and there is cheap labour and good experience of production and processing and attractive local and foreign markets. These all call for the active participation of the parties who involve in the value chain of turmeric from land to consumption. The recent devastation of ginger production from most part of Ethiopia lead farmers shift to turmeric. However, in spite of these, all such huge opportunities, production and productivity of turmeric remained low demanding implementation of all available technologies such as released varieties, suitable site selection, land preparation, harvest and postharvest management practices to benefit the society in the value chain. It is very important to put hands and all capacity together to avert this and benefit the society.   

The authors have not declared any conflict of interests.

The authors thank the Ethiopian Institute of Agricultural Research (EIAR) for funding the study.